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Mechanische camera's
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Mechanische camera's

Apo-Summicron-M 1:2/90mm ASPH.

The 90mm focal length has a special place in the Leica lens stable. Since the early beginnings more than 10 designs have been produced by the Leitz/Leica Optical Design Department. The versatility of the 90mm as a portrait, reportage and landscape lens has been documented by many famous photographers. The Elmarit-M 1:2,8/90mm is one of the very best lenses ever produced by Leica in this focal length, easily surpassing the Summicron 2.0/90mm. The revenge of the Apo-Summicron-M 1:2,0/90mm Asph?
I could use a new 2/90 APO/ASPH for some time and here is my full report.
At full aperture (2.0) we find a high contrast image with extremely fine detail rendered with good clarity and contrast. On axis (center) and in the field (outer zones) and extending to the very corners the minutest detail possible is recordable. The faintest trace of softness at the edges of very fine detail can be detected. Outlines of image details are of superb edge contrast. At f/2,8 the contrast improves a bit and the whole image crispens somewhat, bringing in the finest details above the threshold of visibility. Stopping down after 2,8 only improves depth of field. This more than outstanding behavior holds till f/16. At f/4,0 we find an incredible capacity for recording the finest possible detail with the crystal clear clarity and excellent microcontrast that is the hallmark of the New Design Principles by Mr. Kölsch. Perfect centering, only the faintest trace of astigmatism and no curvature of field added by meticulous engineering make this lens the One To Use.
But hold on!
The current champion is the APO-Macro-Elmarit 2.8/100. Centering and curvature of field are perfect. But in the outermost corners we can detect a softness of details not found with the SAA 2/90. At full aperture (2,8) the image is of very high contrast, exhibiting no flare tendencies. The finest possible details are very crisply rendered on axis and over the whole field, excluding the corners. At f/4,o the faint trace of astigmatism is gone and now we have image recording capabilities of the highest possible caliber. Stopping down to f/8 gives no further improvement, but after this the edges soften a little.
The Elmarit-M 1:2.8/90mm has at full aperture (2,8) image recording capabilities almost the equal of the SAA and the AME on axis. In the field the extremely fine details are very well rendered with a slight softness of the edges. And the crisp clarity of outlines is a bit behind the SAA and the AME. AT f/4,0 the microcontrast improves and now approaches the image quality of the other two. At f/5,6 the EM is on a level with the others at 2.8 to 3.5.
The big question?
These three lenses are among the best Leica has to offer. The EM is a bit behind the other two. Given its performance level, we need the highest possible expertise to approach the limits of the other two. The SAA and the AME are in my opinion equal at comparable apertures, but show a subtly different fingerprint. The SAA excels at image clarity of extremely fine details where the AME excels at the crisp rendering of the same details. For me the SAA is the winner, because it offers its superb image qualities at f/2.0 Gone are the days that one has to excuse the quality on the grounds that full aperture is just that: full aperture. The SAA is one of the very few to offer stunning quality at f/2,0.
Another big question?
What about the 1.4/80 and 1,4/75 compared to the 90/100. The 1,4/80 at full aperture gives a lower contrast image with a tendency to flare.
Fine detail is recorded with good contrast but soft edges. This recording capability holds on axis and only slightly drops in the field.
Extremely fine details are just visible, but it depends on the film if you can see them. At f/2,0 very fine details visibly crispen but the edges stay on the soft side.
At 2.8 the image quality improves but is not on the same level as the 2,8 capabilities of the 90/100 trio.
At f/4,0 we find the quality we already noted in the SAA at full aperture.
Stopping down improves the contrast and the recording of extremely fine detail. The edges of outlines stay a bit soft.
The Summilux-M 1,4/75 at full aperture is better than the 1,4/80 at full aperture. Higher contrast give the extremely fine detail more clarity and sharper edges. Astigmatism is visible which softens the finest possible texture details.
At f/2,0 the image improves a lot and at f/2,8 is outstanding if not superb. Here we see a stop advantage compared with the 1,4/80.
Stopping down brings in the extremely fine detail recording with clarity and high edge contrast.
Overall the M 1.4/75 is a bit ahead of the R 1,4/80. It is questionable if one can see it it in everyday picture shooting. We should be aware of the fact that many photographers do not use their lenses to the optimum level of performance. The comparison with the Summicron 2/90mm is a point. This lens is often praised for its image quality wide open. In comparison to the 6 lenses evaluated here, the performance is not in the same league and under critical inspection and with comparative pictures you see the differences very clearly. But many photographers would not be able to note this performance difference.
All test pictures made on Kodachrome 25 and 64!!
Summicron-M 1:2/28mm ASPH.
Introduction and background.
A few years ago in Solms, I was shown a lens, a compact 1:2.0/28mm lens for M. It was a prototype, to be sure, but it was ready for production, all optical computations and tests were done. On my question why this lens never made it to the production stage, Mr. Kölsch answered, that he expected more performance from a new lens of these specifications. So a new design was created from scratch: the Summicron-M1:2/28mm ASPH., scheduled for delivery early in 2001.
The optical prescription of the lens is quite fascinating. It fits in the genealogy of the seminal Summilux ASPH, a design that decisively departs from the classical Double-Gauss formula. This design-type, now more than a 100 years old, has been stretched to the limits and a performance plateau has been reached. The new Summilux design, incorporates the negative front and back surfaces and the aspherical surface. It is probably the first lens that has been designed specifically around the use of aspherics. Retrofocus designs are a second approach to step out of the shadows of the Double-Gauss formula. More lens elements can potentially improve performance, as more parameters can be controlled. The new Summicron-M 1:2/28mm ASPH picks up design elements of both: the lens group in front of the aperture is an enhancement of the Summilux (front group) design and the lens group behind the aperture fits into the retrofocus family and is a derivative of the 2.8/28 formula. We should not press the point, however, as a lens design is a creative whole and not a mix of ready made components. The message should be that the new Summicron is based on the best design principles currently available in Solms thinking. The location of the aspherical surface is different and probably decisive for this design.
The ergonomics.
The new 2/28 is indeed a very compact lens, comparable to the current 2.8/28 version.
Measurements are (2.8 version in parentheses): length from flange: 41mm (41.4mm), overall diameter: 53mm (53mm), front diameter: 49mm (48mm). Both lenses use filtersize E46.
For a lens with twice the speed this is a remarkable feat. This design indicates the direction of future Leica M designs: compact and high speed and high performance. The somewhat weak performance of the old Summilux 1.4/35mm could be excused with reference to its compactness, which forced the designers in those days to find a compromise between size and performance. Now the circle has been squared.
The lens operates very smoothly, and the aperture ring clicks with just the right amount of resistance and fluidity. When taking pictures with the new Summicron 28, I was amazed how quickly I could focus with the focusing tab and I have to confess that I hardly missed a shot, when focusing moving objects. The depth of field with a 28mm lens, even at an aperture of 1:2 exceeds of course the DoF of the Summicron 50 by a factor of 2, which brings real advantages in street shooting.
The performance.
At full aperture this lens exhibits a high contrast with crisp definition of exceedingly fine detail over most of the image field, softening in the field from image height of 9mm. A faint trace of astigmatism and field curvature can be detected. Stopping down to 2.8 improves the center area (diameter 12mm) and also brings in a higher microcontrast in the outer zones. Corners however lag a bit and stay soft with a limited definition of coarse detail. Stopped down to 4, contrast becomes very high and the optimum is reached with a very even performance over the whole image area, excepting the extreme corners. At 5.6 we se a small drop in microcontrast of the fine textures and from 8, the overall contrast drops a bit. We have to put this in perspective, of course as we relate it to the optimum aperture. At 5.6 and smaller, the Elmarit-M 2.8/28 is a bit behind the new Summicron 28.
Distortion is about the same as with the Elmarit 28mm and vignetting is just visible with 2 stops in the corners at full aperture, about the same as the Elmarit at 1:2.8. In general use, this falloff can be neglected: even on slide film one has some difficulty noticing the darkening of the extreme corners.
Close up performance at 0.7 meters and full aperture shows excellent performance with high contrast rendition of very fine detail.
Night pictures retain high contrast in the shadow areas, and (when exposure is right) finer gradations in the highlights are recorded as well. At least with slide film and Black and White. Bright light sources have cleanly delineated outlines, indicating effective elimination of halo effects. Coma cannot be detected in these situations (light points in the image field).
Flare is very well suppressed in daylight shooting too, in contre-jour situations and when the sun strikes the front lens obliquely. Of course: you can construct situations where secondary images and veiling glare is quite visible, but even here the images retain contrast and some saturation. A lens shade is needed, when the light sources may shine in or close to the front lens. I will give this topic a separate treatment. Leica has redesigned the front part of the lens where the shade is attached for easier handling. All wide angle lenses suffer the same problems here. It is a tribute to the design team that they have given this topic additional attention.
The transition from the sharpness plane to the unsharp areas is relatively smooth, but really out-of-focus areas show the tendency to break up details in coarse and fuzzypatches. There is a certain harshness in the out of focus rendition that is typical of modern Leica lenses. It is related to the level of aberration correction.
The comparison.
The Elmarit 28 at 1:2.8 is slightly behind the Summicron at 1:2, specifically in the contrast in the field. At 2.8 the Summicron is ahead of the Elmarit at 2.8, again in the field and in the rendition of very fine details. This advantage is not lost at smaller apertures. So we may say that the Summicron at 2 is already ahead of the Elmarit at 2.8 and never loses this advantage. Given the very high performance of the Elmarit, these differences at the smaller apertures are not very great, but they are there for the discerning user to exploit.
Compared to the Summicron 2/35 ASPH, the new Summicron 2/28 wins in the department of definition of very fine detail, where the 35mm is of slightly lower contrast. The Summicron 35 however wins in the area of distortion. Stopped down the 35mm lens is a bit softer overall, but we are here discussing differences on a very high level of performance.
If we take a helicopter view of the Summicron line for the M, we can note that the Apo-Summicron-M 2/90 ASPH. is the best overall and at full aperture, closely followed by the new Summicron 2/28 ASPH. The Summicron 2/35 ASPH is third with a somewhat lower overall contrast and a softer rendition of very fine detail at all apertures. The Summicron 2/50 upholds its reputation at smaller apertures, but begins to show its age at full aperture performance. Well even Pete Sampras can be beaten by a younger player.
With the Summicron-M 2/28 ASPH Leica adds a very potent lens to the stable of current M-lenses. Its a full stop ahead in performance compared to the Elmarit-M 2.8/28. The significance of this evolution is not to be underestimated. In the very recent past, it has been normal experience, when comparing lenses, that a faster speed lens would be not as good as the not so fast lens in the same focal length class, and would become better when stopping down, surpassing he less faster alternative because of its inherently higher level of correction. Now we have a lens in the 1:2 category that is even better, objectively, when compared to the 1:2.8 version. The same trend I noted with the Apo-Summicron-M 2/90 ASPH, a lens that is also better at full aperure than the excellent Elmarit 2.8/90mm. It is really progress when we now have transferred the outstanding performance of a 2.8 design to a 2.0 lens. It is to be expected that Leica will improve the performance of a lens, when introducing a successor version. The magnitude of the improvement however is such that we may note a new paradigm for Summicron-class lenses.
All test pictures made on Kodachrome 25 and/or 64!! Additional films used for this test: Ektachrome 400, Elite Chrome 100EC
Elmarit-M 1:2,8/24mm ASPH
The 24mm focal length is new in the M stable. I was a bit skeptical as to its usefulness at first. And indeed it took a while to get fully versed in employing its new perspective. See picture example at end of page.
The Elmarit-M 24mm is without any doubt a masterpiece of optical engineering and within the Leica M range a landmark design. No Leica M user should be without this lens. The M style of photography demands intimate close range photography and the 24 is one of the best lenses to explore this area. It delivers unsurpassable quality in the 24 focal length.
Note the unusually second element and the small number of elements for the complete design. It is this attention to design principles that keep Leica in the front rank of optical design.
Performance of the Elmarit-M 2.8/24mm ASPH
I used two exemplars of the Elmarit-M 2.8/24 ASPH (# 3782523 and #3844221) and compared it to the Elmarit-R 2,8/24. Specs can be found everywhere.
The Elmarit-M 24mm is without any doubt a masterpiece of optical engineering and within the Leica M range a landmark design.
At full aperture the lens exhibits a very high contrast image from center across the whole field. Only the far corners drop in contrast and produce soft details. Over an image circle with a diameter of 12 mm the outlines of subject shapes and details are delineated with superb edge contrast and extremely fine details are crisply and clearly rendered. In the rest of the field the very fine details are crisply attached in the emulsion with extremely fine details visibly rendered but with softer edges. Exceedingly fine detail is just rendered above the threshold of visibility, but with slightly lower contrast.
Going from center to corner the contrast of the extremely fine details drops a bit, but while a bit soft these details are still clearly visible.
Stopping down to f/4,0 the contrast of very fine detail improves and the exceedingly fine detail now is clearly visible. Corners still lag a bit but center performance (12 mm image circle) is at its optimum. This aperture can be called the optimum. Stopping down to 5.6 we see that the finest possible detail crispens a bit, but the outlines of shapes and details starts to soften faintly. Overall contrast thus is a bit lower. It is a matter of priorities which aperture is optimum. I would say that at f4.0 this lens is at its best.
At f/8,0 corners continue to improve where the center now drops in contrast. At f/16 the overall image contrast is lower and very fine detail suffers as diffraction sets in.
At close range (± 70cm) this excellent performance is preserved. A wide angle lens like a 24 is worthless if the close up performance would not equal the infinity setting. Due to aberrations we need to stop down to 5,6 to get the best of performance in the close up range.
Flare suppression is perfect. Night pictures with Kodachrome 64 show excellent gradation in strong highlight sources and distance point sources are clear and without any halo.
Of course some light fall off is visible at full aperture, but in most picture taking situations you can forget about it.
On the bench a faint trace of decentring could be observed. On the other hand flatness of field is absent and astigmatism very well controlled. Coma could not be observed.
Distortion is also hardly observable. Of course when you intentionally take pictures in oblique position the perspective is out of line. Used in a level position this lens is distortion free.
Its view is quite fascinating. I used it in reportage style picture taking situations and could get very interesting pictures at close range. The trick in using this lens is the selection of subject matter at about 1 and 2 meters.
If this is interesting, the whole image will be. Some users might be tempted to go for the grand view. In most instances you will be disappointed as details are small and foreground is excessive.
The M version of the 24 focal length is a lens that is a quantum leap forward in comparison to the R-version. It gives the user imaging quality potential that is a challenge to materialize. Where the R version is quite capable, the M version is just phenomenal.
At full aperture the M version is already almost at its optimum, realizing a long standing goal of the Leica optical designers: best quality at full aperture over the whole image field. This lens is quite demanding on the capabilities of film emulsions. Pictures 0n 400ISO transparency film proved that this lens will show its qualities even when relatively grainy films are being used.
Within the Leica lens range this lens has a premium position. Its angle of view produces fresh views of interesting objects in this world at close range and its optical capabilities add a novel impact to pictures taken with fairly wide angle lenses.
No Leica M user should be without this lens. The M style of photography demands intimate close range photography and the 24 is one of the best lenses to explore this area. It delivers unsurpassable quality in the 24 focal length.
The R-version.
At full aperture the lens exhibits a medium to high contrast in the center, dropping rapidly when going to the corners. Very fine detail is visible with soft edges and a strong presence of astigmatism will wash out the rendition of very fine detail. Also color fringing will soften the edges of the subject outlines. Going to the corners we notice a rapid drop in contrast and fine detail is clearly visible, if with soft edges, At f/ 4 contrast improves and fine detail now is crisply rendered. Optimum is reached at f/8,0 where very fine details are just visible in the center and barely make it in the field.
Close up performance is very good. In the field however the image quality is quite below the one in the center at full aperture and we need to stop done to f/8 to get a decent performance.
Generally speaking the R version performs adequately in most picture taking situations. Some years ago I tested the R version against the Nikon 2.8/24 and I found the outcome a draw.
At optimum aperture of f/8.0 the R-version is almost as good as the M-version at full aperture. That is quite a statement, but it is unavoidable after examining transparencies, b&W prints, mtf graphs and bench results.
All test pictures made on Kodachrome 25 and 64!!
Note of caution
Many users could make a small mistake when comparing lenses. If you would use a Summicron-M 50mm and a Elmarit-M 24 mm side by side and take pictures of the same object at the same distance the Summicron will win. Simply a matter of magnification. As the focal length of the E is half the one of the S any small detail that is reproduced by the E is also reduced twice in comparison to the S. So detail rendition of the S is invariably better. The meaningful comparison would be to take pictures at 100x the focal length and then you will notice that the E is almost equal to the S.
Apo-Telyt-M 1:3.4/135mm
The 135mm has a special relevance for Leica rangefinder users. Anyone will remember the famous Kruckenhauser pictures of skiers in the snow from the 1930's. The standard of performance had been set by Zeiss with the Sonnar 1:4,0/135, that around 1965 reached its then theoretical optimum. The Leitz version improved even on this and with the new Apo-Telyt 3,4/135 the issue is settled one and for all. This is the lens to have and use on a M6 HM or M3.
Image quality of the 135mm M-lenses
Compared as usual to the predecessors, the Tele-Elmars 4,0/135. The T-E has an optical layout, consisting of 5 lenses in 3 groups. In comparison the A-T has also 5 lenses but now in four groups. The T-E is optically unchanged since 1965 and has been given several facelifts. The optical performance of the 4/135 is, even from today's very high standards, outstanding.
Tele-Elmar 4/135
At full aperture the whole image field from center to the outermost corners gives a high contrast image with extremely fine detail crisply rendered.
The subject outlines are sharply delineated and give the image a high sharpness impression. Stopped down to 5.6 the contrast improves a little. After f/8,0 the contrast of the very fine object details diminish a bit. Stopping down further softens the edges of fine detail slightly more. This performance holds from infinity to 3 meters. Centering is perfect (I used an older version #2206407), some curvature of field and a trace of astigmatism can be noted on the bench. This lens is at its top already at f/4,0 and with stopping down loses a bit of its impressive performance.
Apo-Telyt 3.4/135
The A-T at full aperture (3,4) the whole image field from center to corners give a high contrast image with extremely fine details very crisply rendered. Stopped done to f/4,0 the A-T improves visibly on the T-E on its ability to render the finest possible details with excellent contrast and clarity. Stopping down this level of performance holds to the smallest aperture (22) with only very small losses in edge contrast.
This APO-Telyt shifts the performance level of M-lenses to a higher platform. It represents current thinking about optical performance as implemented by Leica. At wider apertures and closer distances the unsharpness area sets in abruptly and the shapes of objects rapidly lose its details. For me personally this behavior is excellent, but bokeh aficionados might be less happy.
The important characteristic of the A_T is its superior clarity of exceedingly fine detail that give A-T images a new look. While for some purposes the T-E gives comparable performance, the A_T excels in a transparency of fine color hues and almost lifelike rendition of very small subject details. In direct comparison the rendering of the same fine detail by the T-E is dull, or when going to the edge soft or washed out. Going one level of detail deeper the T-E produces noise where the A-T still shines.
This level of optical performance is very sensitive to manufacturing tolerances. Computer diagrams show the loss of performance when focus is shifted away from its optimum position. The lavish and some would say excessive attention to production tolerances is indeed needed here. My lens worked flawlessly and had no dust or other blemishes
APO-MACRO-Tele-Elmarit 2.8/100.
I also made a sideways comparison to the APO-MACRO-Tele-Elmarit 2,8/100.
Both the A-T and the AMTE are on the same level of performance. In the far edges the AT is even a bit better. But generally we may now note that Leica M users are very well served and now can produce images the envy of the R-users, who had the advantage in the medium telelens field.
The Apo-Telyt is a truly superb lens. It demands users who are willing and able to exploit to the fullest their technique and do not hesitate to improve on their expertise to match the optical qualities of the APO-Telyt.
Compared to the 2.8/135.
At full aperture the center has good contrast and very fine detail is crisply rendered with adequate clarity. In the field the image quality drops visibly and now fine detail is recorded with good contrast. Very fine detail is washed out by softness of edges and low contrast. Stopping down improves somewhat. Generally this lens is miles behind the 3,4/135.
All test pictures made on Kodachrome 25 and 64!!
Leica Macro-Elmar-M 1:4/90mm
Every advantage has its negative counterpart. We may assume that there is nothing free in the universe. Gain here, loose there. The Leica rangefinder system is a beautiful construction, which adds great clarity to an accuracy that is good enough for a surveying instrument. The system however is built around a complex mechanical-optical design that has some limitations. The principle is quite simple. The rotating movement of the distance ring on the lens is translated into an axial movement of the lens unit. The back of the lens unit, the thread, is shaped like a curve with a certain steepness. This curve acts as a wedge that displaces a roller arm, which in turn moves a rangefinder prism that projects an image of the object on a second prism. This second prism also receives an image of the object through the finder and because of the beamsplitting design of the prism, the eye now sees two superimposed images. 
Moving the distance ring allows both images to coincide. The maximum distance of movement for the roller cam is about 5 mm and the maximum axial distance for a 50mm lens from infinity to 0.7 meter is 5mm too. This is a 1:1 reduction of the lens movement and the cam movement. But the accuracy is not linearly distributed over the gradient of the cam. If we change the distance setting from 5 meter to 2 meter (a difference of 3 meters) the axial displacement of the lens is 1mm. The cam movement then is also 1 mm. In order to translate this movement to the tiny change in the angular movement of the prism, the steepness of the cam must be considerable. If we If we now change the distance setting from 1 meter to 0.7 meter (a difference from 30 cm), we can observe that the axial movement is 1.5mm and the movement of the roller cam is also 1.5mm. We understand that the relative steepness of the curve, the reduction mechanism and the axial movement of the lens have a limited scope. If we wish to focus more closely to the object, we need a longer curve (the total length of the wedge must increase), which is impossible as the diameter of the bayonet mount is fixed. Or we need to change the shape of the curve and so reduce the accuracy of the measurement. We should not forget that Barnack designed this construction 70 years ago and that it is still the best we have. The longer the focal length, the more the limitations of this mechanical transfer will be approached and the shortest distance that can be rangefinder coupled is restricted.
The second limitation of the rangefinder mechanism is the parallax, but I do assume the reader is familiar with this one. The upshot is a limit on the range for the near focus distances that can be photographed with the M-camera. This is a pity, because there are many photogenic opportunities in the range between 50cm and 1 meter.
Macro solutions
Leitz knew this too and in the past several solutions have been proposed. These are Leitz-typical jewels of mechanical engineering. In many instances we see an extension tube with an optical attachment to correct the parallax and can be used for a limited distance range. Collectors know the names by heart, like SOOKY and SOMKY and OMIFO. The handling was also Leitz typical and not the most elegant or efficient to use.
Optical evolution
The evolution of the optical design at Leica has been focused, since 1980, when the new focal length of 75mm lens was announced, on the optical improvements of the existing range of lenses. And with great success. Several of the current Leica lenses for the M-system belong to the world’s best lenses and all are part of the top three of the best lens systems of the world. But the photographic opportunities have not been expanded. A 35mm wide angle lens, now and then delivers the same style of pictures, even if the new aspherical version has improved imagery. This changed when the new 24mm was introduced in 1996 and especially with the new Tri-Elmar-M from 1998. Now the M-user could with an easy switch change between three focal lengths from 28 to 50mm. The dynamical style of reportage photography could be enhanced with a new perspective.
The close range however was not the strong point of the M-system. Standard and wide angle lenses could be focused till 70cm, but the low magnification ratio did not allow the subjects to be reproduced large enough on the negative.
Macro-Elmar-M 1:4/90mm and Macro-Adapter-M
Now Leica has filled the gap wit a new lens: the Macro-Elmar-M 1:4/90mm. With the use of the Adapter the lens will focus till 50cm, and reach a magnification ratio of 1:3 and that is quite nice. The lens itself is a four element collapsible design, focusing till 77cm. Collapsed it is a very compact unit and with the Elmar-M 1:2.8/50mm will present a very handy travel set. In combination with the Tri-Elmar you have a range of focal lengths from 28-90 and a distance coverage from infinity to 50cm. This is quite versatile.
The danger is that the new 90mm lens will be seen only as a macro lens. In fact it is a very compact, extremely high performance lens that can be used for reportage style photography, where its high class definition can add a new sense of gritty reality to the pictures. (see below)
Some people will always put a question mark on the longevity of a collapsible construction. I am one of them. But my heavily used Elmar-M 2.8/50 is still impeccable and is being monitored on the optical bench for any loss of performance. There is none! The lens hood is most effective and can be put on the lens as a protection. The lens hood will never win a design price and personally I had hoped for a more pleasing design.
With the Macro-Adapter attached to the body and lens the useable range extends from 77 to 50cm. The lens has two focusing scales for both ranges. The Adapter is in fact a thick extension tube with two M-bayonet mounts and an optical attachment with three eyes to put in front of the three eyes of the camera. This one is crystal clear and does not distort the image in the finder. Previous Leitz constructions were not that good. There is additional parallax compensation and this means that two topics must be addressed. The normal frame lines in the finder of the M-camera are too generous in the near focusing range: there is less on the negative than you see in the masks of the finder. Normally this reduction is about 5%, which is not very important. But in close up photography you may miss important edges. The problem of parallax is the second topic. Both these effects make it difficult to get an accurate framing. You must make test pictures to get a good feeling what is being recorded when you frame with the lines in the finder. I used a page from the Donald Duck and you can see quite clearly what is being captured. You might even tape thin strips on the focus attachment to guide you.
In the macro-position the lens works very efficiently. The rangefinder patch is quite enlarged and the alignment of the images is slow: the distance to cover in order to super impose the finder and rangefinder images is quite large. But is very accurate: the thickness of a Eurocent makes a big difference in the rangefinder images.
Depth of field is very thin: at f/4 and magnification of 1:3 it is 3mm. At f/11 it has been extended to 9mm. You need some are when selecting objects to photograph at this magnification.
Optical performance
A 90mm lens with aperture 1:4 was already available in 1930 and a collapsible version could be bought since 1954. These specifications for a most modern design do not seem ‘sexy’, but the optical designer has a different view. The demand to create a compact and lightweight lens, that performs excellently at all distances, including the macro range, is not an easy one to fulfil. That is why Leitz had in the past always two versions of the 90mm lens, one optimized for the normal (infinity use) and one for the more close-up use. The evolution of the 1:4/90mm lenses is quite interesting. The 1930 version had the classical Elmar/tessar design with three elements, the last being a cemented doublet. The contrast was quite low and the definition of fine detail was just acceptable. The big problem with a 90mm lens with only a few elements is the wish to combine high contrast and high resolution in a lens that inherently has a large secondary spectrum and a high amount of curvature (high Petzval sum). In 1968 leitz surprised the world with a new 4/90mm lens with only three lenses and two different glass types.

Elmar-M macro
It had an astonishingly good performance. It was only a few years on the market and now is a collectible item, a pity. In 1973 The Elmar-C was introduced for the CL body. This lens had four separate elements with four different glass types. The performance was much higher than before and now we have a high contrast image, good resolution from centre to mid zones and only the cornets were lacking in brilliance. A similar design was used in the latest Elmarit-M/R 2.8/90 lenses.
It would have been easy for the design team to adopt this solution. But then the macro quality is lacking. So a new calculation and optimization was done and the result is an outstanding lens. Again with four separate elements, but now the diameter of all lenses is almost the same. This helps to ease the rays through the surfaces with a small deflecction of the ray at the surface.
If you look at the classical triplet design, you see that the middle lens is much smaller in diameter. Here the rays from the bigger front element are steeply deflected and this causes more aberrations.
At full aperture the M-E-M-90 delivers a high contrast image and a very high resolving power (definition) over the whole frame from centre to extreme corner. Curvature and astigmatism are absent and decentring as a measure for quality control during manufacture and assembly is not noticeable. The resolving power in the centre is above 150 lp/mm and even in the extreme corners is still around 100 lp/mm. Many lenses would be happy to have 50 lp/mm in the corner with this contrast.
At 1:5.6 contrast increases a bit due to the reduction of internal reflections. At 1;8 the optimum is reached and this performance holds till 1:16. Only at 1;22 there is a noticeable drop in micro (edge) contrast. This is one of the few lenses that perform equally well at all smaller apertures.
The most interesting resolution can be found between the 10 lp/mm and 20 lp/mm and at these frequencies the edge contrast is very high and we do not detect any colour fringing. In fact one wonders why the lens has not been given the APO designation. The Leica designers are very strict and they did not give the coveted star to the M-E-M.
In the near range from 50cm to 1 meter the performance is exemplary good. In the range from 50cm to 80cm, the overall contrast is a bit lower and the definition of fine details less crisp, but you will not notice this aspect, as the magnification ratio compensates visually the slight reduction in contrast. Due to the slim depth of field you will most often stop down anyway.

Vignetting is 1,8 stops and can be detected as is the distortion of 1%, that will be noticed at very high magnifications.
To answer this question: no, the macro-adapter cannot be used with other 90mm lenses, as the cam of the M-E-M is specifically designed for the macro adapter.
The other lenses
The R-system has the redoubtable APO-Macro-Elmarit-R 1:2.8/100mm . a most versatile lens. A real comparison is not possible as we have one the one hand a six element design with special macro lens components and a physically large lens. On the other hand a four element design with slender dimensions. Still it is of some academic interest to see what the performance differences are. The M-E-M delivers at full aperture a fraction more of performance at medium distances than the A-M-E-R. The edges of the lower frequencies are somewhat tighter defined and the M-E-M gives a crisper presentation of the facts. Presumably the lower number of lens elements and the careful choice of the glass types are the cause of this behaviour. At 1:5.6 the tables are turned and now the A-M-E-R has a slight advantage, which holds till 1:8. It might be the inherently higher level of correction that is at its optimum at the medium apertures that is responsible.
The Apo-Summicron-M 1:2/90mm ASPH delivers outstanding quality at the wider apertures, but it is logical to assume that at 1:2 the A-S-M-A is not as good as the M-E-M at 1:4. Again it is the higher overall contrast and the very good edge contrast that make the day for the M-E-M. This comparison is not really fair as the Summicron has a two stops advantage at maximum aperture. When we compare both lenses at 1:4 at medium distances , we may note that the Elmar reproduces the fine detail with a crisper edge. The Summicron at 1:4 is somewhat softer. The large front lens of the Summicron collects some non-imaging forming light from the surroundings (especially in back-lit situations), that softens the overall contrast somewhat. I would hesitate to call it veiling glare as this is not the case. In comparison the images of the Apo-Summicron seem a fraction overexposed in relation to the Macro-Elmar.
At smaller apertures, the Apo-Summicron is as good if not better than the Macro-Elmar.
These three lenses deliver high quality imagery of a very high order. Many people will not note any difference at all. Pushed to the limits or using the lenses at their designated optimum role, you will be able to see the subtle and important differences.
With the Apo-Summicron and the Macro-Elmar, Leica has given the user a difficult choice.
As a related remark, I would comment on the often heard statement that an 1:4 lens is not good for reportage work and thus has no place in the M-System. Such an opinion is not based on real insight. Most pictures of Cartier-Bresson were made at aperture 1:8 and no one will deny that his work is reportage style pur sang. It is true that at 1:4 we have a limit when using the lens in situations where the ambient light level is low, but it not the case that the photographic reportage is restricted to the so-called ‘available-light’- photography. And in many cases a slight fill-in flash does the trick when the speed of the lens is too low. We should not forget that in many situations the depth of field will dictate the use of a smaller aperture. The simple yes/no discussion should be replaced with a more mature when/if discussion.
The other contender is theVoigtlander Apo-Lanthar 1:3.5/90mm. This is a Double-Gauss lens with six elements. At aperture 1:4 this lens is a bit behind the M-E-M, specifically in the corner performance where the Lanthar records 70 p/mm against the Leica lens with 100 lp/mm. Edge contrast is also lower, as we see more colour fringing with the Lanthar than with the Elmar.
With the exception of the Elmar-M 1:2.8/50mm, the Macro-Elmar must be the smallest optical package in the M-system. And with the exception of the Apo-Summicron 90mm and the Apo-Telyt 135mm it is one of the best overall performers. Its image quality in the near focusing range is unequalled in the M-range and this brings the added value to the lens. It does not replace one of the existing lenses, but brings new pictorial possibilities into the reach of the M-photographer. To identify this lens as a pure macrolens would be to restrictive. It is a very fine general purpose lens, that will deliver stunning images with today’s black and white and slide material.
Leica  Summarit 1:2.4/40mm
Intro: the ultimate limits of the classical designs.
The Summarit 2.4/40 is a double-gauss design and by now it should be clear that the limits of this species are being approached. It is significant to note that historically the two most used design types (the triplet and the double-gauss both were adapted to 35mm use by Lee of Taylor and Hobson in the 1920’s). Given the constraints of this 6-element design hardly any improvements can be expected. That is why Leica changed to the ASPH designs in the 35 and 28mm focal length.
Zeiss, with the 1.4/50mm, used a DG design and it is interesting to hear what Mr Woltge (previous chief designer of Zeiss) has to say. The lens is optimised fully within the design parameters and better quality is only possible when one employs more expensive glass. Given the price of the Planar 1.4/50 one may assume that this has not happened. Compare the prce and performance of the Summilux-R 1.4/50 New and you know what decisions the Leica designers made.
Anyway: the Summarit is a landmark design as it is designed by Mr Kolsch himself using all tricks of the trade.
The Summarit 1:2.4/40mm on test.
At full aperture overall contrast is very high and very fine detail is very crisply defined with excellent clarity over most of image area (till about 16mm image height). The extreme corners are quite weak when we are looking for fine detail definition, but overall outlines are well preserved. On axis the finest detail is recorded, but this drops gradually after image height of 10mm where details are soft. Flare is very well suppressed. At f/4 there is a visual improvement of the rendition of very fine and extremely fine detail over the whole image area (excepting the extreme corners) and now we have imagery of a very high order. Micro contrast of the smallest textural details is high and there will be only a few film emulsions that can cope with this information overload. At 5.6 and 8.0 the image quality improves a bit and the current target of an outstanding lens (above 50% contrast for the 50 lp/mm norm) is reached if not exceeded.
The overall fingerprint of the Summarit is close to that of the seminal Summicron 2/35 ASPH and I suspect that the Summarit is the best of its kind given current knowledge. The same is the case with the new Elmar 3.5/50 in the 0-series, which is also an optimization of that other design type, the triplet (here in Elmar/Tessar formula). Both the Summarit and Elmar would be worthy of being fitted to the M-body.
The comparison.
The Summicron-M 2/35 asph has at wider apertures a somewhat more even performance over the whole image area. The drop in performance with the Sumarit is however, quite gradual till 12mm iage height and so may not be detected easily.
The Summarit however is much better than its closest rival: the Summicron-CL 2/40. There are interesting differences: the CL lens does not record such fine detail as the Summarit , but shows also a difference in design approach. The CL version has better quality on axis to the detriment of the outer zones (beyond 6mm image height) which are quite low in quality , where the Summarit has a more even and generally higher level of performance, in accordance with current thinking. In the past Leica photographers were more focussed on the image in the center of the negative, presumably.
The classical Summicron-M 1:2/35mm (of 1979) is also of a different design philosophy and exhibits a mixed character with excellent quality in the center and over a large part of the negative area, but now the residual aberrations take their toll and the softer edges of main outlines and the fuzzy edged of finer textural detail give an image that is overall clearly weaker.
In my view then the Summarit could be the last of the Mohicans: the final level of performance that a classical double Gauss design can attain. While most people may assume that the Minilux is a better idea of a mousetrap, that is a simple P&S camera with a good lens, it is in fact a challenge to every M user. try to get the most out the Minilux/Summarit and you are qualified for the next stage: the current M-lenses.
Let me end with a personal note to show that I am human after all:
in my neighbourhood there is a small photo shop, manned by a 76-year old shopkeeper, who happens to use Leica M3 cameras. He has been treated for cancer several times, which did not change his view on life.
Of course I bring all my colour negative and slide work (not Kchrome) to him and we discuss the old days and the vanishing of the classical values in photography. Some day I gave him two rolls of film (Konica 50ISO: a very good film and with outstandingly accurate colours). When the prints returned we looked at them and he said: here you have real Leica quality and there I am disappointed: what did you do?
Well: the ‘real’ Leica pictures were with the Summarit. The not-so-good were made with the Apo-Summicron 2/190 ASPH.
Summicron-M 1:2/35 mm ASPH, plus: 35 mm comparison
On 19 June 1997 Leica officially announced the new Summicron-M ASPH (35mm).
The Art of Perfection
Leica is clearly practicing the art of perfection with its new generation lenses for the M line. The new Summicron ASPH vital measurements can be found on the Leica website.
The new lens has the now familiar concave outer surfaces of the front and rear elements as has the Summilux ASPH. The weight increase of 100 gr can be attributed to heavier glass used in the construction. Particularly the rear most two lens elements are really fat.
High contrast and crisp, very fine details at full aperture
On test the new lens showed at full aperture a high contrast image with excellent rendition of very fine detail in the center (a circle with a diameter of ± 12mm). Very high micro contrast crispened the edges of the very small details. Going outwards the image becomes softer at the edges gradually losing its very fine details when approaching the far out corners. Light fall off could be seen in the extreme corners, but is in practical shooting negligible. The current Summicron-M has the same overall contrast), but loses out very slightly in microcontrast. The rendition of very fine detail is a bit softer and the gradation of small textures is slightly more washed out. The light fall off is a bit more pronounced, but still uninteresting. Most spectacular is the flatness of field of the ASPH. Here we have a lens which at full aperture gives a completely flat image! The current Summicron is visibly more 'curved'. You need to see the comparative pictures to believe the stunning advantage.
Optimum already at f/4,0
From f/ 2.8 to f/5,6 the ASPH reproduces the detail with increasing crispness and at f/5,6 reaches its optimum. Then the center qualities are extended into the far corners and we have an extremely high performer over the total negative area. The current Summicron follows exactly the same behavior, but in the corners never reaches the qualities of the ASPH. In the center at f/5,6 the claim of Leica that the ASPH has a better resolution of very fine textural details than the current one is borne out.
However the German words ("deutlich uberlegen") when translated mean "clearly superior" do the current one a disfavor. The difference is there to be seen but not as clearly as this description suggests. From f/8,0 the quality drops a little as the edges of small details are softened. But for practical purposes both lenses can be used from 2.8 till 16.0 without reservation.
Flatness of field is stunning
In a nutshell: the new lens wins in the corners and has a better micro contrast which gives it the edge in the resolution of extremely fine details which are also rendered more clearly and crisply. The flatness of field at full aperture is stunning. Flare suppression is excellent, but the ASPH is not perfect: in the corners and sometimes (in very unfavorable circumstances well into the outer zones) you still detect traces of coma.
From f/4,0 however the differences are a little academic. They are certainly there, but is it important in practice?
The comparison between Summicron-M 35mm, Summicron-M ASPH 35mm and Summilux-M ASPH 35mm.
I conducted my usual tests on Fuji Velvia, complemented by the benchmark analysis. I now made the test pictures at three different distances:1,2 meter, 4 meter and 10 meter. As usual. all pictures are shot in very low contrast situations to give a better idea of the overall contrast and the micro contrast. I also shot a series of pictures of a street scene with the sun just above the horizon and shining directly in the lens. The image of the sun however was blocked by an object. The sun itself therefore was not in the picture. This test is used to see how well flare is reduced and how well the lens renders the fine details of the scene and how good the separation of highlight detail is.
All three lenses came out very well and in comparison with other makes can all be qualified as excellent. There are a number of noteworthy differences. You must remind yourselves that the differences noted are only visible when using the utmost care in taking pictures. Note also that Leica is competing against itself when introducing new lenses.
First the lenses at f/2,0.
Summicron-M ASPH 35mm gives a high contrast image image with excellent micro contrast and a crisp rendition of extremely fine detail from center to the well into the outer zones. Light fall off is noticeable, but restricted to a very small zone. Flatness of field is outstanding as is the definition over the whole image area.
Summilux-M ASPH 35mm also gives this same performance, but the finest details are rendered a fraction softer at the edges. The difference between Summicron-M ASPH 35mm is the coverage over the image field. Center sharpness is a mite better with Summilux-M ASPH 35mm, but this lens loses more detail when going to the outer zones. This is visible at 30 times enlargement. So it is not easy to say which lens is better. I would prefer to call it a difference in fingerprint or characteristic of image rendering.
Summilux-M ASPH 35mm follows the classical¹ pattern of extremely high center quality, becoming less so when going outwards. Summicron-M ASPH 35mm is a new pattern concentrating on even coverage over most of the field. The difference between the center performance of Summicron-M ASPH 35mm and Summilux-M ASPH 35mm are in my view slightly academic, but they are there to note (on the bench at least!).
Micro contrast
Summicron-M 35mm follows the pattern of Summilux-M ASPH 35mm: very high center sharpness and a gradual leveling off towards the corners. Summilux-M ASPH 35mm has a slighty better micro contrast and a crisper delineation of very fine detail than the Summicron-M 35. At least in the center. The outer zones show less advantage. Summilux-M ASPH 35mm has at f/2.0 less light fall off and a much flatter field, and equals Summicron-M ASPH 35mm in these respects.
Light falloff
At f/1,4 Summilux-M ASPH 35mm gives more light fall off than Summicron-M 35mm at f/2,0 and now also exhibits more curvature of field, slightly less than Summicron-M 35mm at f/2.0. Summicron-M ASPH 35mm is definitely better at f/2,0 than Summilux-M ASPH 35mm at f/1,4 and Summicron-M 35mm at f/2,0 is almost identical to Summilux-M ASPH 35mm at f1.4. The overall characteristics of Summicron-M 35mm are similar to the one of the Summilux-M ASPH 35mm. It seems as if the Summilux-M ASPH 35mm is an Summicron-M 35mm with one full stop more. In addition Summilux-M ASPH 35mm has slightly higher micro contrast, less vignetting, better separation of highlight details and the flatter image field than Summicron-M 35mm. But its color rendition is warmer than that of Summicron-M 35mm which is quite neutral. Summicron-M ASPH 35mm also is a little on the warm side. You just cannot have all.
Vignetting is completely gone at f/2,8 with both ASPH. and visible in the extreme corners of the Summicron-M. This lens has a rear lens element with a bigger diameter than the ASPH versions, in earlier days an argument for a design with inherently less light falloff.
Close up performance (±1 meter)
is good for all three lenses. The f/1,4 aperture of Summilux-M ASPH 35mm however shows curvature of field and vignetting. Here I would not go into a detailed comparison. All three are very competent in this area, with Summicron-M ASPH 35mm slightly ahead.
At f/2,0 flare and stray light are extremely well repressed with Summicron-M ASPH 35mm, it gives excellent separation of highlight details, virtually ghostless images and the fine details are clearly defined with very good gradation and color nuances. It also exhibits a very crisp image of brilliant clarity. The image of Summilux-M ASPH 35mm at this aperture is more flare prone at least in this situation. The larger frontlens just captures more oblique lightrays, that can soften the image a bit.
The Summicron-M 35 is on the same level as Summilux-M ASPH 35mm in this respect. The smaller frontlens helps to suppress flare and light reflections a bit more.
Interestingly at f/1,4 Summilux-M ASPH 35mm is better than at f/2,0, because the absence of diaphragm blades do not reflect some of the light, that at f/2,0 has an effect as the diaphragm is closed a little more and the light rays are reflected into the lens.
In another situation (portraits taken with very strong backlighting, but no internal reflections or flare) both the ASPH¹s could take advantage of the better micro contrast and produced images with slightly better retention of fine details in the highlights. The differences are however quite small.
Here we took night pictures at 1,4 and 2,0 and daylight pictures at 5,6 to 8,0. I would consider the performances as equal. In one series the Summicron-M came out as the winner with a very small margin, in other the Summicron-M ASPH took the lead.
Pictures at infinity setting in my view are sharp. Some correspondents questioned the ability of modern lenses to be critically sharp at infinity. Here however the expression that the weakest link is responsible for the strongness of the chain is true. The tripod must be supported by heavy weights, not only its own. The film must be extremely fine grained, and the slightest overexposure is killing off the image quality. Any nature photographer can tell you the additional precautions that are necessary to ensure a stable platform.
The lenses at 4.0 and 5.6.
At these apertures all three lenses are at peak performance. All the virtues of the design are now clearly visible. Extremely fine details from center to corner, very smooth color hues in small object areas, crisp rendition of object outlines, both large and small, very good suppression of flare around strong light-points (sun reflections in water droplets) and that famous clarity and impression of 3-dimensionality of Leica lenses. Generally speaking, I could not detect any important or significant differences between the three lenses at these apertures.
Theoretically the better microcontrast of the ASPH lenses should become visible in the definition of the fine details. But handheld shooting and the grain limit of the films used (Kodak Ektachrome 100 SW and Fuji Provia 100) possibly suppressed this potential advantage.
Summicron-M ASPH 35mm and Summilux-M ASPH 35mm are the more modern designs and are capable of better image quality than the Summicron-M 35mm.
The differences are visible, but you must compare the images side by side to see it. Summicron-M ASPH 35mm is a superb all-round lens with a very even and excellent performance. Its images have the special Leica characteristic, that can be seen in most modern Leica third generation designs: image clarity of a very high order. Summilux-M ASPH 35mm is a lens that brings Summicron quality into an f/1,4 design , but this superior performance at full aperture forces the designer to balance the optical parameters in a different way.
Summicron-M ASPH 35mm and Summilux-M ASPH 35mm have a different fingerprint and therefore a different audience and photographic capabilities.
If you need F/1,4 there is no alternative. If F/2,0 is enough for you the flavor of Summicron-M ASPH 35mm and its price/volume are very attractive. In performance it and its sibling Summilux-M ASPH 35mm are in the same league.
The Summicron-M 35 was and is a excellent lens. It is a tribute to the designers of that lens that it took Leica 20 years and the most modern design- and production technology to bring optical quality to a higher level. The photographer, willing to exploit the superior qualities of the ASPH lenses, must be willing to upgrade his technique also.
Leica M 21mm and ASPH versions
 Super Angular 4,0/21mm (#1645508):
At full aperture light fall off is quite noticeable, so is curvature of field. Distortion is hardly visible.
At full aperture the image field from center to a radius of 5mm gives good sharpness and medium contrast. The object outlines are well defined, fine and very fine details are a little bit soft. Extremely fine details are very soft with low contrast. So in fact hardly visible. From 5 mm the image contrast drops rapidly and from 8mm vey fine detail ist just noticeable and fine detail is visible with low contrast. From an image height of 11mm astigmatism begins to reduce the visibility of fine detail. Subject outlines are rendered softly and in the corners even these details are unsharp.
Stopping down naturally improves the quality. Contrast however stays at a low to medium level. Stopping down to f/8 enhances contrast a little, extremely fine details are visible, but not in the corners and the outer zones (in horizontal view: the long side of the negative). At f/11 the optimum is reached and from f/16 the performance drops. There is slight decentring.
Generally speaking: this lens at full aperture gives a good performance in the center and if the clear rendition of very fne detail is not the prime objective this aperture is usable. Modern performance is not possible even at optimum aperture, however.
Super Angulon 3.4/21mm (#2057735):
At full aperture distortion is negligible, light fall off is reduced and curvature of field well corrected.
At full aperture the center image within a radius of 8mm gives a crisp rendition of subject outlines and fine details.,the corners being very soft. Very fine details are rendered with medium contrast from center to 6mm and with lowish contrast from 6mm to the corners. Extremely fine detail is just visible, with very low contrast and soft edges from center to about 10mm radius, vanishing in the outer zones.
At f/4 this lens is a marked improvement on the SA 4.0.
At f/5,6 contrast is improved and extremely fine details are now clearly visible till the outer zones, the corners still being soft.At f/8 the optimum is reached, the rendition of extremely fine details is good with a medium contrast.
At f/11 and smaller the performance drops.
Generally speaking: this lens is a very good performer. its fine qualities only restricted by the presence of astigmatism that reduces contrast and crisp rendition of very fine detail. There is slight decentring:
Elmarit-M 2,8/21mm (#3685701):
At f/2,8 the light fall off is slightly below SA 34 levels. Flatness of field is less well corrected as is distortion.
At full aperture the center image with a radius of 10mm gives a slightly crisper image than the SA34. The generally somewhat higher contrast results in a more clear delineation of fine details. Outer zones and corners are soft.
The general performance of the E is s little above that of the SA 34 wide open. This is partly due to the reduction of astigmatism, resulting in improved rendition of fine details.
At f/4 extremely fine details are visible with good contrast from center to a radius of 6mm. From there to the corners the image details become progressively softer, but fine details stay within detectable range,
The optimum is reached at f/8 with a good reproduction of extremely fine details till the outer zones. The subject outlines, especially in the outer zones have slightly soft edges, giving an overall impression of a smooth but not brittle sharp image. Stopping down to f/11 and smaller reduces the quality. Decentring was not measurable.
Generally speaking: this lens is a commendable performer and a slight improvement on the SA 34. It does not bear the Leica badge with full honour.
Elmarit-M 2.8/21 ASPH (#3787298, 1997):
At full aperture contrast is high and extremely fine detail is very crisply rendered from center over a radius of 11 mm. From then the contrast of edges drops a little but is still vastly superior to all its predecessors. Astigmatism and curvature of field are almost fully corrected. Subject outlines and fine details are extremely sharp and clearly almost lucidly rendered. In the outer zones and the corners this superior performance drops naturally. The overall image quality is a quantum leap forwards in relation to all predecessors and I may add competitors.
To set it in perspective: the performance at f/2.8 is better in all respects to the SA 34 at f/5.6.
Or: the max resolution of the SA 4 at f/,0 is about 70lp/mm with very low contrast where the ASPH at f/2.8 has 125lp/mm at high contrast.
At f/4,0 contrast and the clear rendition of very fine details improves, with the corners still lagging behind.At f/5.6 the optimum is reached with exceptional performance including the far outer zones.
From f/8.0 the performance drops ever so slightly and at f/16 is visibly below optimum.
Decentring is not measurable.
Overall: this lens gives outstanding image quality at full aperture and improves till f/8.0.
It is by a great distance the best 21mm in the Leica stable and the only choice for the person who needs superior performance from a 21mm lens, with aperture of 2.8.
Close-up performance.
A 21mm lens by nature shows a great deal of empty foreground, which could be filled with some objects close to the lens. The essence of the 21mm is the enclosure of an interesting foreground motive by a large space. It is of importance to see how the lens behaves at distances around 1 meter.
Super Angular 4,0/21mm (#1645508):
At f/4,0 vignetting is quite visible. fading away when stopping down. But even at f/11,0 there is a small brighter spot in the center of the negative.
Contrast is low at all apertures. At f/4,0 good sharpness is available over a substantial portion of the negative, the corners stay behind. At f/8.0 the whole field gives sharp details, excepting the outer corners. From f/11 sharpness drops.
Super Angulon 3.4/21mm (#2057735):
At f/3,4 vignetting is much reduced and at f/4 the level is about the same as the SA 4 at f/8.0 Itself the SA 3,4 is fee from vignetting at f/8.0.
Overall contrat at full aperture is visibly higher, but it is the micro contrast that produces small details with a high level of crispness. At f/5.6 the whole negative area is filled with sharply rendered small details
Elmarit-M 2,8/21mm (#3685701):
At f/2,8 the corners are visibly darker, but vignetting is gone at f/4.
At full aperture the overall contrast is a bit below the SA 3,4, but from f/4,0 the differences are not important. The Elm however reproduces very fine detail just a shade crisper. From f/5.6 the performance evens up over the whole image and we have a excellent image with crisp very fine detail till the corners.
Elmarit-M 2,8/21 ASPH (#3787298, 1997):
At full aperture it is slightly less than its predecessor and just there vignetting is no issue from f/4.0.
At full aperture overall contrast is higher than the Elmarit-M 2,8, but more important the high level of micro contrast gives a clear and finely rendering of very fine image details over the whole field, including the extreme corners. Quite impressive is the even performance from center to corner over the whole aperture range.
Flare suppression:
The Super Angular 4,0 has at f/4,0 a good suppression of flare and handles oblique stray light surprisingly well. The Super Angulon 3.4 at full aperture is quite prone to flare, it gives large halos around light sources. The half stop to f/4.0 improves matters to the level of the SA 4, giving a clue of the difficulties of stretching the aperture a half stop.
The Elmarit-M handles light sources quite well at full aperture. In strong backlight the silhouettes of tree branches are dark (no leaking of lihgt around the corners) are sharply outlined.
The Elmarit-M ASPH improves on this, especially at full aperture the suppression of halos might me termed quite tight.
Performance at infinity.
This a difficult topic.
Various people have discussed the performance of extremely wide angles at infinity and found the image quality a bit below expectation when compared to a lens with a smaller angle of view. As we always use the same scenes as a comparison, we could compare the far distance scene as imaged with a Elmarit-M 28mm (latest generation and a superb representative of its kind). It is immediately visible that the 28mm gives a sharper image, with extremely fine detail crisply rendered.The overall image also has a clarity and lucidity that is difficult to quantify or even to describe objectively. The 21mm lenses in direct comparison are softer, lack the overall clarity and crisp reproduction of very fine details. It is all there to seen, without doubt, but to put it in a different way, the image details are fading a little.
The optical progress can be easily followed in the discussion below with the Elmarit ASPH reaching a very high level and the only one to be favorably compared with the 28mm.
The Super-Angulon 4.0 reproduces fine detail with a low contrast at full aperture, and with a slightly fuzzy edges. Stopping down improves of course the image. The slight vagueness however never disappears. The Super-Angulon 3.4 with its half stop advantage is the better lens by a margin. The fuzzyness is visible too. While stopping down brings in more detail, with a higher level of sharpness the crispness is lacking. Tough objects like distant trees with small branches lack blackness and contrast.
The Elmarit-M at full aperture shows very fine detail, but it is not rendered sharply and extremely fine detail is lost. One needs to stop down to f/5,6 recover these extremely fine details and get a good level of sharpness.
The Elmarit ASPH gives better imagery at full aperture. Sharpness is higher, and extremely detail is just detectible. At all apertures the ASPH gives a visibly sharper image and the level of just detectible details is higher (more details that is). At f/4.0 performance is as good as the predecessor at f/8,0.
Is a direct comparison between lenses of different focal length acceptable?
Not really! The reproduction factor of the extremely fine details is higher with a 21mm than with a 28mm. Even if the grain and the film would allow it, the 21mm needs a higher magnification to show the same details at the same format and therefore needs a higher degree of optical corrections at a higher spatial frequency. That is something to ask!
A comparison can be made when we use the same reproduction rates. I always a reference distance of 100 x focal length, which gives subject detail the same format irrespective of focal length.
The upshot of this infinity test is simple: extreme care must be taken if ones wants best quality at infinity: stable tripod, correct exposure, distance setting at infinity. low speed film. The test shows clearly that performance at infinity with the latest generations of 21mm is on a very high level. When comparing results one should take into account the reproduction factor and all other image degrading components.
I also made a test to ascertain if the performance level changes if one sets the focusing ring just a fraction before the infinity mark and so use the DoF to secure good sharpness. This is the so-called hyperfocal distance. The drop in performance between these two settings is clearly visible. So if you need the best image quality at infinity set the distance ring at infinity and forget about DoF notions here.
I also noted that image quality will be severely less if the objects at infinity are overexposed, which is quite often the case with small objects (like trees) against the sky.
Elmar 3.5/50 red scale
There is some discussion if the socalled Redscale Elmar 3.5/50mm is an improved version compared to previous versions.
All books note that around serial number 905000 a recomputed and improved Elmar has been introduced. The alleged new calculation is based on a comparison of the curvature of the front element, which is slightly less strongly curved than the prewar type. It is also researched that some other versions had still different curvatures (not as flat as the Red scale but flatter than the prewar or postwar black scale versions).
The original 1926 Elmar had glass types (front to back: SK7, F5, BK7, SK15).The Red scale is supposed to have (SK14, F8, LF5, BaSF10). Data from article in LHS England #48.First of all: small changes in curvature, certainly from the front element of the Elmar are of often insignificant value for the design.
This element does not take the burden of correction of aberrations. The second lens element does. And lens bending as it is called is often done to accommodate other changes. If bending is needed for optical correction it is for coma and spherical aberration, which is difficult to optimize in a 4 element triplet.
Secondly: a change in glass types is not always done to improve the performance. Sorry to destroy another myth.
Sometimes a glass type becomes extinct and a new glass has to be found and some re-calculation is needed. But if the lens is already very good (or can not be improved) a re-calculation to accommodate the new glass does not infer better performance. Sometimes a glass type has been changed for easier production or coating purposes or better or smoother grinding. Not of these in itself does improve the quality measurably. The 4 element triplet is quite resistant to improvements when changing glass types. What you need is a high index crown glass with matching negative flint glass.
SK7 has 1.61, BK7 has 1.52, and SK15 has 1.62 (rounded figures).
SK14 has 1.60, BaSF10 has 1.65, but is not a crown but a flint.
Kingslake in Lens Design Fundamentals uses several sets of glass types to correct a 4 element triplet but notes that is does not make big changes, unless all refractive indices are above 1.60. This is already the case with the 1926 version (except BK7).
So we cannot in itself conclude that on the basis of these data there is an improvement of design. Schott indicates in the glass catalogue two types of glass (preferred and not preferred). The newer glasses are mostly of the preferred type, and the previous ones of the not-preferred type.
I do not believe that the change gave much improved performance. And I am not ruling out a small drop in performance in the outer zones from the type with the preferred glass.
Now the serial number. I have these numbers in my database:
Elmar 3.5/50 from 904.001 to 910.000 and allocated in 1951 (note NOT produced in 1951).
The next is 941.001 to 950.000 and allocated in 1952.
It is highly unlikely that Leitz would change a design in the middle of a production run.
I can almost with certainty declare that the indicated serial number of 905000 for a change in design is wrong, at least not based on any plausible facts or authoritative written sources.
Studying the available documents there is indeed a change in glass types (which not necessarily means a change to an improved design) and I would locate that change at serial number 955001. (might it be that the original author of the # 905001 did misread the German handwriting???, which is indeed very hard to encipher) It is a guess but that could have occurred as a preparation for the bayonet version from # 1140xxx.
Now the 4 element design has an interesting additional story. The 4 element lens is just capable of correcting the 7 basic aberrations. Read my book for details.
To give the expected performance there may not be any change in production tolerances as the design is extremely sensitive to assembly and manufacturing errors.
A 5 or 6 element design can give the same or even somewhat better performance with a much higher latitude in tolerances. Is this the explanation that the Japanese in the 1950’s when they introduced their cameras used 5 or 6 element designs which were not much better than the 4 element German ones but much easier to produce in large quantities? 
 Leica M Summicron 50mm comparison
 At last the results from a comparative evaluation and test of the Summicron 50mm generations.
On the bench we have
    * a Summicron Collapsible with some coating defects,
    * a Summicron Collapsible in excellent as new condition ,
    * a Summicron Rigid (7 elements),
    * a Summicron DR (same generation) and
    * the current Summicron-M (third generation). 
General remarks
There is a significant difference in optical performance between the C and the R, NO difference at all between the R and the DR and important differences between the R/DR and the N. The differences between the C with defects and the clean one are remarkably small. A drop in contrast, a higher level of flare and a loss of micro contrast when recording very fine details are visible. These differences might or might not be important depending on user-expectations and shooting circumstances. All remarks below refer to the clean version. The Summicron family from its first inception represents state of the art performance. Results were examined under several viewpoints. The practical testing has been done at 1 meter and 5 meters and with 10 and 30 times enlargements. The pitfalls of testing and the responsibility of the tester in presenting the results have to be made quite clear at the beginning.
As an example: consider the rendition of the extremely fine details.
Here the C is good at 1 meter and 10 times, but weak at 5 meters and 30 times.
The N is superb in both tests at 30 times and here it is the emulsion that is the weakest link.
So if your normal shooting practice concentrates on handheld shots at a distance from let us say 1 meter to 2,5 meters, you use 400 ISO B&W film or the older generation transparencies from 200 ISO, and your enlargement requirements are modest, the C will suit you very well and the differences with the other types are maybe not so significant. If you have the same set of requirements and use the N, you are under-utilising its performance potential. In fact you may use only 30% of its optical performance capabilities. Of course you will see differences, but you might not b able to recognize them.
The Collapsible (#1377201) at full aperture shows a low contrast image with soft outlines and the delineation of fine and very fine detail also quite soft in the center. The outer zones show astigmatism, reducing the rendition of very fine detail, but fine detail is visible, but soft. The corners are quite weak with only the fine detail and the outlines just visible. At 2,8 the contrast is a little better, but you really need f/4,0 to see the extremely fine detail, but even now its edges are very soft. At f/5,6 the very fine detail is now rendered with sharpish outlines. This performance level has nw extended over the outer zones, only the corners lagging quite severely. At f/8,0 spherical aberration softens the center and from f/8.0 the general performance drops a little. There is no curvature of field, hardly any vignetting and no chromatic aberrations to speak of. Centering is OK. At all apertures to f/4,0 there is a veiling glare softening the overall image and suppression of bright spots is also weak.
The Rigid and DR are identical in performance (#1956284 and # 2116804). At full aperture the overall contrast is medium but the rendition of very fine details is a class better than the C. The outlines, fine detail and very fine detail are clearly visible with good sharp outlines and a fine micro contrast. Extremely fine detail is on the soft side. The outer zones still show astigmatism and in the extreme corners only fine detail is visible. At f/2,8 the contrast is better and at f/4,0 the optimum is almost reached with a center that has a sharp and contrasty rendition of extremely fine detail. The outer zones are noticeably softer (and show traces of astigmatism) and the corners are again lagging. At f/5,6 spherical aberration softens the center, but the outer zones now have a sharp representation of extremely fine detail. From f/8,0 the quality drops slightly and more so at f/16. Flare is well suppressed, as is chromatic aberration and curvature of field. Centering is OK.
The Summicron-M new.
At full aperture a high contrast image is rendered with very crisp rendition of extremely fine details from center to the very corners. Astigmatism is gone except in the far zones. Exceedingly fine detail is now visible with good micro contrast. At f/2,8 this lens has perfect qualities. From f/8,0 spherical aberration very slightly softens the center and from f/8.0 micro contrast drops a little. Flare is very well suppressed and all other aberrations can be neglected. This lens at f/2,0 surpasses in all respects and criteria the DR and Rigid at f/4.0 and f/5,6. Especially important and very visible is the clarity of the image and the extremely well preservation of exceedingly fine details. This lens can render details in the order of a factor 2 smaller than its name bearer the Summicron of the first generation. . To save some email: no I am not testing the out of focus rendition. Conclusions: The C is adequate for out and about photographic activities and may have very pleasing subject rendition. The DR and the Rigid are much better, but no match for the New. Optical progress here is quite visible, but special precaution is necessary to exploit this level. The C and DR/Rigid are not as good as the best of modern emulsions. The New however challenges the capabilities of the best emulsions and the expertise of the photographer.
Some physical measurements to show the difference between Collapsible and Rigid/DR: frontlens of the C is about 2 mm smaller in diameter than the R/DR, but the rear lens is about 1 mm larger. From bayonet flange to front the C is 39,2mm and the R/DR is 43,5mm. The rear element of the C is almost flush to the flange while the R/DR is recessed about 5 mm. Optical progress between the earlier first generation Summicron and the latest one (not the last one: a new version will someday be available) shows stunning results. Has the user accommodated to these new heights of image quality? First of all I did not find any relation between the overall optical quality and the maximum resolution figure, still sometimes used as a yardstick to image quality. Well it is not. The Summicron 3gen has a lower value here than the Rigid one, but a much higher level of image quality. Secondly I noticed that in many out-of-pocket picture taking and even some serious tripod work of high contrast scenes, that the Collapsible held its own better than would be expected from the figures and measurements.
Look at the figures for a circular zone about 2 mm large at a distance of about 8mm from the center. Here the C is a little unsharp, fine details has very soft edges, the very fine details are sagitally and tangentially different because of astigmatism, but anyway again very soft, extremely fine details are hardly visible and even finer structures are not recorded. On film only the fine details and outlines will be visible, the rest will be below the grain threshold and will not be recorded, at least not with film-emulsions of the '50s. The same spot for the R/DR shows some flare and low contrast and also astigmatism but less as with the C. The very fine details are sharpish, but not crisp, and extremely fine detail is soft. Exceedingly fine detail will be lost in the grain structure and is hardly visible.
The new Summicron has a high contrast image here, no trace of flare and astigmatism, extremely fine detail is very crisp and even exceedingly fine detail is rendered clearly, but beyond the capability of most film/users. Given these figures we can assume that even for high quality pictorial work the rendition of fine detail and especially the outlines are instrumental for the overall image quality. We do not see the several aberrations separately. Most aberrations generate soft spots and some will change shapes of spots (coma as example). So the result of taming the aberrations is a crispening of very fine detail over the whole image area. It were the Japanese who noted that a very nice sharpness impression could be conveyed by optimizing the outlines of details, that is the 5 lp/mm threshold. Yes that is true, most photographic optics are not required to produce more than 5lp/mm or at most 10/lp/mm. Here we note (see an earlier post) that modern emulsions have a MTF of about 100%.
Now we can understand why older Summicrons still perform so well: the 5 and 10lp/mm limit is very acceptable and should have been in the early '50s a revelation.
Especially the evenness of performance over a large image field is important. We can now understand why so many persons can hold to the statement that Nikon, Canon, Pentax produce very sharp pictures.
These lenses are optimized for exactly these structures. In practical situations we are not using the full potential of the modern Leica lenses (maybe the effort to get the most out of them is too high a price to pay, but why do we pay the hefty amounts of money for Leica glass) and as long as we go on exploiting the fine details limit and dare not go further, some revelations will not be discovered. It is perfectly legitimate to have personal lens-acceptance-procedures as are reported on the LUG. Many of the finer points of Leica quality will not be revealed in this procedure. The sparkling clarity of the finest details, rendered crisply and finely graduated with excellent color neutrality is an everlasting joy and quite addictive: once you noticed it, you will not settle for less. But then the Leica M has more uses: photojournalists and other professionals will look for different criteria.