History and background
There is an enduring fascination for limits in photographic culture and technique. The drive to engineer and use the fastest film speed, the highest shutter speed, the shortest focal length, the quickest motor-drive and the fastest lens continues till this very moment. In several cases, the need to push a limit is sensible, but in many cases it is not. Every time you extend a limit, you will approaching another one, Most parameters are part of a system of mutually influencing forces. Faster emulsion sensitivity implies larger grain sizes, increasing the signal to noise ratio of a sensor will also increase the noise and a compact zoom lens implies a smaller aperture.
Pushing back frontiers is not the province of the Startrek crew exclusively. In the photographic industry mechanical and optical designers and engineers have relentless opened up new horizons. But sometimes a natural limit is being encountered. The top speed of the horizontally running focal plane shutter had been fixed at 1/1000 of a second for a very long time. With improvements it has been possible to push the top speed to 1/2000, but then the adverse forces start to counter act any further progress. In this case the physical boundaries and possibilities can be calculated and predicted with some precision and confidence.
Lens designers are working with a larger range of uncertainties. Optical improvements do not advance in a linear fashion. Too many variables and constraints must be accounted for.
This state of affairs is particularly true for that specific class of lenses that are adorned with the title of superfast lens. In the current context this applies to standard lenses with a maximum aperture wider than 1:1.4. In most cases the aperture has been set at 1:1.2. Only a very few lenses have been designed in the wide angle or short telephoto category with apertures of 1:1.2. But the main battleground for all manufacturers has been the standard lens. There are practical, and optical arguments for this choice. For a long period the standard lens (with focal length between 50mm and 58mm, sometimes stretched to 60mm) has been the pre-eminent choice for documentary available light photography. It is in these circumstances that the light collecting power of the high speed lens was most required. Optically the balance between bulk and speed could just be held, in particular with the inherently bigger slr-lenses.
The race for the fastest lens started in Japan in 1953 with the introduction of the Zunow 1.1/50mm lens, followed in 1954 with the Fujinon 1.2/50mm. Both lenses were for the Canon and Leica CRF with screw thread mounts. In those days the fastest normal lens had an aperture of 1:1.5 and then a 1.1 was really impressive. A very high speed lens suited the available light photograpers who had to cope with slow speed films and very coarse grained higher speed ones, like the Agfa Isopan Ultra or Record. And then one stop more of lens speed implied one higher shutter speed or added exposure in the shadows. Canon and Nikon responded in 1956 with a 1.2/50mm lens with seven elements (canon) and a 1.1/50mm lens with nine elements (Nikon). At that moment in time both Nikon and Canon were already focused on the SLR concept, but Canon did introduce the 0.95/50mm lens for the Canon 7 in 1961 to demonstrate their prowess in matters optical. No more very high speed normal rangefinder lenses were made in Japan until 1999 when Konica produced the special edition 1.2/60mm lens for M-mount.
Canon introduced a 1.2/58mm lens for the Canonflex and a 1.2/58mm lens with aspherical surfaces in 1971. The first series used aspherical surfaces that were grinded by machines that were manually operated. Only later (but long before Leica) did Canon switch to a fully automatic grinding process.
Canon's 1:0.95 lens "holds razor sharpness even at full aperture" (original excerpt from advertisement), but this statement is quite optimistic. In fact the Canon lens wide open is a good practical example of the working of spherical aberration. The sales brochure of Canon also describes the lens as being four times brighter than the human eye. Here Canon is a bit too modest. The Leica brochure of the Noctilux 1:1/50mm describes the lens as being even faster than the human eye. Studies of the eye have revealed that the maximum aperture of the eye lays between 1: 2.4 to 1:6.8 depending on age and situation. The Summarit line of lenses equals the maximum aperture of the eye.
The quest for superfast standard lenses has always been associated with a large dose of prestige. The availability of a very high speed lens has always been seen as the icing on the cake. A camera system with superfast lenses was accepted as a true professional product. Many camera and lens manufacturers have been producing standard lenses with apertures ranging from 1:0.95 to 1:1.2 and with focal lengths from 50 to 60mm. These lenses were made for CRFs and SLRs. The marketing argument has been focused on the use in low ambient/natural light or even the absence of illumination where the just hand-holdable shutter speed could be the dividing line between a good and a lost picture. A high speed film where the sensitivity threshold had been pushed to the maximum level was also a trick of the trade. Working at the limit of the possible has its own charm and knowing that you are using the best lens adds to this mood. A superfast lens is loaded with aberrations and very difficult to manufacture within the required tolerances that the design demands to tame the optical rays.
Almost every design relied on spherical lens surfaces and the designer needed additional lens elements and more exotic properties and/or daring shapes to get a decent quality at the widest apertures. The pictures that could be made with these lenses could be described as acceptable only with a benevolent approach. Canon went over the top with its 0.95/50mm lens for its rangefinder camera. On the other hand we have learned from the Startrek series that you need to go where no one else has gone before in order to improve your knowledge and experience.
Around 1970 lens design had been improved, but the only rangefinder left was the Leica. The lens mounts for slr-cameras are inherently bigger and most manufacturers of SLR lenses have stayed on the safe side of 1:1.2, and often used aspherical lens surfaces to improve the image quality. Since the advent of digital cameras the interest in superfast lenses has become marginal. Only Canon has produced a 1:1 design for the EOS series, but the most recent incarnation of this lens has its aperture reduced to 1:1.2.
The competition in the SLR arena for the highest speed lens continued from 1960 to 1985 between several manufacturers, but the CRF scene was abandoned around 1965 leaving Leitz as the sole survivor. Undoubtedly the Leitz designers knew about the Canon 0.95 lens and were aware of the need to produce a superfast lens themselves. Their research into the design options indicated that the only solution for a lens that combined a compact mount with good performance was to use aspherical surfaces. The aperture of the original Noctilux was set to 1:1.2. A wider aperture required a bigger mount and it might also be assumed that the size of the lens elements was too large for the aspherical grinding process.
The Noctilux had internal competition from the Summilux 1:1.4/50mm that offered comparable performance at a much lower price. Still the 50% additional light that falls on the film surface could become important. When working in very low light levels it makes sense to put the minimum exposure just on the edge of the toe area of the characteristic curve of the film. Here any additional light that can be used to activate the AgX crystals is welcome. Nowadays the S-shaped curve that for such a long period in photographic technique defined the tonal reproduction has been made obsolete by digital capture where a linear response is the normal case.
The successor of the original Noctilux widened the maximum aperture to 1:1 and used only spherical surfaces. The performance wide open is quite good and much better than what the Canon 0.95 offered. Both lenses used seven elements and no doubt the new glass types available to the Leica designers and their experience with high speed CRF lenses gave the Noct-design this much improved performance.
The actual scene
The Noctilux 1/50 stayed in production for more than thirty years (from 1976 to 2008). It has been a steady seller and the last hundred lenses (in a special edition) were sold out in a whisker. A new version was expected but it was assumed that the lens would have the same parameters but fitted with new glass with aspherical surfaces. The choice for an aperture of 1:0.95 is quite daring, not only because the 11% increase in pupil diameter does pose challenges for the aberration control, in particular the chromatic correction for the widest aperture which is troublesome if you also want to correct the other aberrations like coma and spherical. As outlined above the aperture of 0.95 has not the best of connotations given the Canon experience. Leica chose this aperture presumably to create enough distance from the previous version to generate new sales and also as a definitive proof that the Leica design expertise could succeed where historical predecessors could not. In my discussions with Mr Lee I came to know him as an avid student of optical history.
Below I have constructed a table with the vital statistics of current Leica lenses and their immediate predecessors. Note that the Summarit is the only true 50mm lens.
The new NX 0.95/50 asph. offers many improvements compared to the previous version. Gone is the focus shift, the presence of coma has been visibly reduced and stopped down the lens equals and even surpasses (slightly!) the performance of the SX 1.4/50 asph. The older Noctilux performed quite well stopped down, but did not reach the quality of the Summicron lens at comparable apertures. The Noct did exhibit a slight softness at smaller apertures not found in the Summicron. The effect of the focus shift can be blamed for this behavior, but also the chosen balance of aberration correction is responsible. The new NX 0.95 has a more rigorous correction of aberrations over the entire field.
Wide open the differences are less pronounced with the previous version, but interesting enough to analyze.
The design of the lens is state of the art with a floating element, aspherical surfaces and a selection of new glass types specifically selected for this design.
With 700 grams this lens is not suitable for prolonged and casual use. By the way: the original Canon 0.95 lens weights over 600 grams! and the previous Noct sets the scale to 630 grams. The focusing is very smooth and even over the full travel of the distance scale. There is not the faintest resistance noticeable of the working of the floating element. In this respect the new NX improves on the SX 50 asph. With sensitive fingers you could just notice a hint of resistance. To hold the dimensions to acceptable sizes the distance ring is quite thin-walled and if you press too hard with your fingers on the mount, a perceptible stiffening is the result.
The use of the viewfinder magnifier is required even when you have a body with the 0.85 finder. M8 users really need the 1.4 version of of the VM.
The finder of the camera is only slightly blocked by the lens mount, but the intended use of the NX will not be hampered by this restriction of the full 50mm view. On the M8 the blocking is even less visible.
Wide open the lens shows a certain softness of major subject outlines. The lower contrast of the high frequencies (fine textural details) softens the edges of the low frequencies (outlines of major subject shapes). Stopping down to 1.2 does improve the overall contrast and from 1.4 the performance is comparable to that of the current SX 50mm with the exception of the outer zones where the SX has the edge and also shows less vignetting. Attached to the M8 these differences will be less pronounced due to the cropping of the viewing angle. The bo keh of the lens is wide open extremely pleasant with very smooth gradation and subtle shape representations. On the other hand the lens at the wider apertures does show veiling glare when strong light sources are just obliquely shining into the lens. Secondary reflections, often a nuisance in high speed lenses, are well suppressed and indeed hardly present. Coma while not fully reduced, is much less visible than what could be seen in the previous version.
Noctilux 1:0.95/50mm ASPH.
This lens is still referred to by Leica advertising as faster than the human eye. This is not true: any 2.8 design has a wider aperture than the human eye, but the eye is unsurpassed in its retinal ability to capture light photons. Nonetheless: such a wide aperture is still a big challenge for any designer. The Leica team has created a lens that is certainly close to the theoretical optimum of this type of high speed lenses. Leica has burdened itself with the drive to develop high performance lenses in the smallest footprint possible and this goal adds additional demands on the designs. If you could work without space limitations and without the fact that a lens needs to be produced at a certain cost and within existing production facilities, the sky might be he limit. But that is not the case. The Noct ASPH is a true Double Gauss system and one needs to stay in this kinship when designing such high-speed lenses. The older Noct version shows the resemblance, but that is only superficial.
Note that the back group (behind the stop) of the Noct ASPH is derived from the Summilux ASPH, but that the front group has a split front lens with an additional air lens. This is quite difficult to mount with the required precision in a production situation, but Leica excels in this domain. The required precision of all new lenses is much higher than what you may know from other designs.
The performance wide open of the Noct ASPh is not significantly improved compared to the old Noct. Indeed it is difficult to improve on the severe vignetting of the older Noct as the requirements for the mount (M bayonet and the front diameter of 60mm are identical). It is some feat that the lens could be stretched to 0.95, after all an enlargement of more than 10%. When using these lenses on the M8(.2) the issue of vignetting is less important, but still very visible.
Wide open the definition of the Noct ASPH and the older Noct is of comparable low contrast, but the new version shows some visible improvement. The 40 lp/mm have a higher contrast at the center of the image and the corners and edges are improved too.
The main improvement can be seen from the graphs when the lens has been stopped down. Below are examples at f/4 as being representative of the general behavior. Note the much improved contrast for the 20 lp/mm and 40 lp/mm. Note too the remarkable bulge of the 20 lp/mm ad especially the 40lp/mm for the older Noct. This is the visual representation of the focus shift that affects the older design. The new design is outstandingly good at f/4 and this is absolutely an achievement.
The claim that the new Noct is as good as the Summilux 50 ASPH at the smaller apertures is substantiated by the diagrams showing the MTF at f/5.6. The differences in the curves are not substantial and not visible in practical photography. Left: Noct; right Summilux
The floating element improves the close up performance, but one should not expect wonders form this feature. Stopping down is still required when best image quality is required. In general use this lens does behave as a high performance standard lens at all distances and apertures from 1.2 and there is no indication for the traditional compromises that have been the hallmark of previous super-fast lenses. Throwing all the partly conflicting requirements into a basket (size, weight. volume, performance, vignetting, close up performance, reduction of focus shift, haptics and so on), it is unlikely that a better lens can be designed in the near future.
Some optical aspects
The current generation of CRF lenses has reached a very high level. Automatic lens improvement programs are universally employed and their use has reduced the design period for a lens from years to months. The programs are constantly improving and research into new designs brings new insights. A lens database with 25.000 different designs is not uncommon. Still there is a wide gap between theory and practice. If you add physical requirements like size and manufacturing cost into the equation, the number of useful designs shrinks rapidly.
All superfast CRF lenses are based on a basic Double Gauss design, but with the number of lens elements increased to seven and even nine elements. Within this limited design space the number of options is infinite, but the challenge is the same: to deliver excellent definition at all apertures and object magnifications (distances from camera to object).
Let us take a look at one of the first superfast lenses for CRF camera to understand what is at stake. The Zunow 1.1/50mm from 1953 has for unknown reasons the lens assumed a kind of cult status.
Wide open at 1:1.1 the lens exhibits a very low overall contrast. There is a small area in the center of the image where subject outlines are recorded with soft delineation. Finer details are not recorded at all or are quite blurred. The lens shows strong spherical aberration, quite visible astigmatism, curvature of field and coma too. The better MTF values at the edge of the image are the result of a strong portion of vignetting, that reduces the number of marginal rays reaching the film plane and this in itself improves the definition. On stopping down to 1:2 the central portion of the image crispens visibly, but fine detail is still quite blurred. A significant focus shift is visible and the outer parts of the image hardly improve. At 1:4 the focus shift is very pronounced, especially in the definition of fine detail. Astigmatism is clearly visible and the edges are fuzzy. Curvature of field is hardly corrected. At 1:8 overall contrast is good and fine detail, at least in one direction, is crisply rendered in the outer zones of the image.
When we evaluate this performance with modern eyes, it would not be acceptable. Set in the context of the period, the image quality is not that bad, compared to other lenses. As a comparison, you may analyst the MTF graphs of an older Nikon 1.4/50mm lens from the same generation of lens designs.
Note that this lens wide open at 1.4 has a very low contrast too, but astigmatism, and curvature of field are well controlled. When stopping down to 1:4, there is a major improvement in definition of very fine detail and only a small occurrence of focus shift. The outer zones show good delineation of subject outlines but fine detail is fuzzy and blurred. Overall this lens shows excellent performance and is even better than the Leitz Summilux-R 1/4/50mm lens from 1969! We might take this date as the moment when Japanese optical design forged ahead and Leica designers retreated in their cocoon.
The aspherical revolution within Leica started with the arrival of Mr. Koelsch, originally from Zeiss, and since then the Leica CRF lenses have been improved beyond the wildest dreams.
High speed lenses share a number of difficult challenges: Spherical aberration (SA) occurs when marginal rays (the rays entering the lens at the edges) focus on a different plane than the paraxial rays (the rays centered around the optical axis of the lens). This error becomes more pronounced when the lens diameter is bigger (as is the case with the high speed lenses). Coma is basically the same phenomenon as SA, but for skew rays entering the lens in the principal plane (the plane that contains the optical axis). The worst villains are the oblique rays entering the lens from object points that lie outside the optical axis and its plane. These rays create astigmatism, a problematic aberration for high speed lenses. Add to this list the correction for curvature of field, the vignetting and the chromatic aberrations, particularly in the blue region of the spectrum and you may see the challenge. Remember too that many aberrations grow in magnitude by the third power when increasing the aperture. In the case of the Leica CRF lenses an additional requirement is the physical size of the lens. The smaller the lens size, the more difficult the aberration correction.
Since around 1990, the Leica design approach has been to deliver CRF lenses with optimized performance over the full aperture range and with a strong emphasis on the wider apertures. This approach has driven the MTF values to very high values over the whole image area, in many cases approaching the theoretical maximum. The resulting image formation favors overall clarity, crisp definition of fine detail, fidelity over an extended subject depth and subtle reproduction of tonality in hues and greys. This fingerprint is markedly different form that of previous generations of Leica CRF lenses. Some Leica users look favorably upon this classical fingerprint and would like to see modern designs with this classical look. This is precisely the gap that is being filled with the Voigtlander lenses from Mr Kobayashi. Zeiss with the ZM lenses occupies a middle ground which is located between both extremes.
The NX 0.95 is the most recent addition to the Leica CRF scuderia employing aspherics and floating elements. When comparing the MTF graphs you can appreciate the quantum leap forward at the widest apertures. At 1:0.95 astigmatism is well controlled as is curvature of field. Overall contrast is low to medium, but the focus shift when stopping down is very well controlled. This implies that spherical aberration has been reduced to low amounts, but one cannot expect a lens with such a wide lens diameter to have crisp definition of fine details. And where fine detail is soft, the delineations of major subject outlines will be soft too. To get sharp edges at subject outlines, we need lots of high frequencies to create this sharp boundary. The performance of the old Zunow lens at 1:1.1 can only be described as a last resort when you desperately need that picture. The NX at 1:0.95 performs so well that you hardly will guess that the picture was made with a superfast lens. At this point in the report, we need to take great care in examining the performance profile of the NX. When testing a lens, and even when just examining the results of the lens, it is quite easy to select and present the good, the bad and the ugly aspects of a lens. The occurrence of vignetting is such a case. The technical data sheet reports a vignetting value of 20% at the edges or more than two and a half stops. There are picture situations where you will very clearly see this strong darkening in the edges. But there are also many instances where the vignetting is negligible. We should also be aware of the optical specifications. A superfast lens with a wider angle of view will exhibit vignetting, caused by a number of factors: size of mechanical mount, cosine 4 law, and image distortion. There is a trade off between distortion and vignetting and the Leica design favors a low level of distortion, in my view a fine choice. This discussion is not meant to diminish the effect of vignetting in the Nx 0.95 but to indicate that we should differentiate between an optical error and an optical given. Focus shift on the other hand is an error that can be corrected without severely effecting other aberrations.
Wide open the NX 0.95 is sensitive to the occurrence of flare and secondary reflections. See picture below. One should take some trouble to prevent strong light sources to shine obliquely onto the lens surface. The previous Noctilux design was not better in this respect and one should have hoped for an improvement in this area. The lower overall contrast wide open has already been mentioned. Residual aberrations and internal reflections may be responsible for this behavior. The contre-jour scene shows that the black stems of the flowers get a blue cast In higher contrast scenes the lower contrast wide open is not detectible and the image offers excellent quality, and one would not assume that this picture is made with a lens at aperture f/0.95.
In situations with dark areas in the scene, the penetrating power of the lens to detect and reproduce detail is reduced. In this picture we see also the occurrence of the blue fringes at the edges of black/white transitions. This phenomenon is a chromatic aberration and is almost impossible to avoid in high speed lenses. The correction of the blue part of the spectrum for this type of lenses cannot be accomplished by simply selecting exotic glass types from the glass catalogues: it is a balancing act between all aberrations, focal length, back focus and so on. The previous Noctilux lenses also showed a significant amount of blue fringing. But is was less visible. Many pictures were made on black and white film, color film was less responsive in the blue region, most pictures were taken in artificial light where red is over-represented.
Bo-ke(h), one of the prime characteristics of the previous Noctilux has been well preserved in the new NX 0.95. Unsharp highlights are rounded and have homogeneous illuminance.
Performance at smaller apertures.Stopping down a fraction to f/1.2 increases the crispness of the image visibly. And from aperture f/1.4 the NX 0.95 behaves as if it were a current Summilux-M 1.4/50 Asph. with the exception of the flare propensity and the color fringing both of which diminish when stopping down. At this point we may note the dilemma for the Leica marketing department: one could have introduced a new 1.2/50 design with outstandingly good properties, but such a lens would be very close to the Summilux 1.4/50 Asph design and offer only a half stop more speed which in the current digital world is less impressive than it was in the past. Stretching the aperture to f/1 or a bit wider, makes more sense, but then some compromises are required. These have been discussed in this text.
The new NX 0.95 combines many of the characteristics of the previous Noctilux 1/50 and the Summilux-M 1.4/50mm Asph in one design. Stopped down it delivers state of the art image quality and wide open the performance has been optimized in such a way that it can be used at all distances and ambient light levels (clear daylight and near darkness). In particular I would like to mention the improved imagery at close distances which allow for strong portraits with a minimal depth of field, and a clearly defined sharpness plane while maintaing pleasant out of sharpness outlines. The manufacturing quality of the NX is superb and there is no reason to be afraid that the lens will not focus correctly on any Leica M body with a well adjusted rangefinder. The absence of focus shift is another characteristic that needs to be mentioned in a positive sense. The historical fact that the original Noctilux 1.2/50 had to be hand adjusted to find the best balance between focus shift and rangefinder alignment is a thing of the past.
Most classical Leica high speed lenses suffered from curvature of field and astigmatism. The new NX is practically free from these aberrations. The result is a pictorial smoothness over the full image (capture) area that especially wide open delivers a sense of depth and clarity not seen in a superfast lens before.
While the lens is a major improvement on the predecessor, some character traits are not changed: the propensity to flare, the blue fringes and the softer representation of subject outlines. It is a matter of great progress in a superfast lens that these are the only aspects that deserve critical attention.
This lens is a specialist lens, price tag and size/weight put it in a category of its own. If you can see the added value of the unique performance characteristics for your type of imagery and accept a lengthy learning curve to get the best out of the lens, a new pictorial style might be your reward.
The SLR Magic HyperPrime Cine T095
Very high-speed lenses for photographic cameras are quite rare in modern times. Nikon limits the high-speed lenses to 1:1.4 and Canon has a few 1:1.2 lenses. The designations vary of course: we have high-speed, very high-speed, ultra high-speed, extremely high-speed and so on. There was a time that even a lens with aperture 1:2.8 was considered a high-speed lens. The photographic language is quite nebulous when technical aspects have to be described or classified. The border between macro- and micro-photography is not clearly defined, nor is the dividing line between wide-angle and super wide-angle and so on. It is best to stick to numerical and factual descriptions when possible. There is a certain magic attached to lenses with an aperture of 1:1. They are are described as being faster (allowing more light transmission) than the human eye. You will find this claim in the current brochure of the Leica Noctilux-M lens). I have no idea on what fact this claim is based upon. The human eye has a maximum aperture between 1:2 and 1:3, but the retina is much more sensitive to light than what we have in films or solid-state sensors.
Lenses with apertures around 1:1 for the 35 mm format are rather scarce and not without reason. Movie-cameras (especially the 8mm and 16 mm versions) have traditionally been fitted with lenses that have apertures around 1:1.1 and 1:1.3. When the format, is smaller, the lens can be smaller and this facilitates the design of a wider aperture. The practical limit is basically determined by size and weight. The Voigtländer Nokton aspherical 1:0.95/17.5 for MFT bodies has 13 elements in 9 groups, a weight of 540 grams, a diameter of 63.4 mm and a length of 80.0 mm. In this case (and quite usual) the advantages of the small capture format are not exploited. The classic Nokton 1:1.1/50 mm for 35 mm photography has a 7 elements in 6 groups, a weight of 430 grams, a diameter of 70 mm and a length of 57 mm. This version has the overall looks of the famous Noctilux 1:1.2/50 mm for M-cameras, but operates in a different performance league. The well-known rule in optical design says that performance can be higher when the lens grows in size. Look at modern movie-lenses and you will see the truth of this statement.
The reference for lenses with apertures around 1:1 is the Leica Noctilux-M 1:0.95/50 mm ASPH. The basic parameters are: 8 lenses in five groups; floating element; two aspherical surfaces; weight: 700 grams; diameter; 73 mm; length: 75 mm; filter size: 60mm
The Noktor HyperPrime lens by SLR Magic, based in Hong Kong, has been introduced in 2012 and immediately drew much attention because of its maximum aperture of T0.95, its large size and the fact that is was available in M-mount, making it a direct competitor of the Noctilux-M lens. The lens has been designed primarily as a Cine lens. The fact that there are no click stops for aperture selection and the reference to T-stop are a reminder of this origin.
The basic parameters are: 12 elements in 7 groups; all surfaces are spherical; weight: 975 grams; diameter: 73 mm; length: 95 mm; filter size: 62 mm.
The ergonomics of the NHP-lens are on first handling, comparable to the NX-lens. Both have very solid-feeling mounts and the size of the NHP gives a good grip. The focus movement of the NX is smoother that that of the NHP, where one has to use more force to change the focus setting. The focus and aperture rings of the NHP are identical in size and it is easy to select the wrong ring when you have the camera/lens before your eyes. The bayonet mount fits very tight to the M-body and some might be a bit uneasy with this fit because of a potentially higher wear factor when changing the lens often. I checked the fit with several M-bodies and all did match, with the exception of the new M (240), but that was still a prototype.
At maximum aperture any lens with a speed of 1:0.95 has an extremely shallow depth of field. At a distance of 1 meter the DoF is 2 cm; a distance of 2 meters gives a DoF of 8 cm and a distance of 3 meters gives a DoF of 20 cm. At wider distances the DoF becomes a comfortable 50 cm ( for 5 meters). The calculated DoF figures are, regrettably!, still based on the size of 0.03 mm for the circle of confusion, which is too large for critical work, especially with digital files that can easily be studied at 100%. The factual DoF figures are therefore lower and the required accuracy is in the region of 1 to 3 %. This holds not only for the mechanical precision, but also the optical precision. The NHP scores well in both departments.
The NHP is the only lens that offers a maximum aperture of T0.95; the Noctilux-M has a maximum aperture of F0.95. Theoretically there is a difference between a T-number and an F-number. The F-number for aperture stop is simply the calculated relation between focal length and diameter of the front lens. The T-number for the aperture stop refers to the measured value of the transmitted light (energy) through the lens, and includes the influence of vignetting and the transmission of the glass used in the design. Optical glass can have a transmittance of close to 100% and when used (with effective anti-reflection coating) there is no difference between both values. For the NHP there is a claim that the T0.95 corresponds to an effective F-number of 1:0.92. Meaningful measurements that can differentiate between these numbers are not possible with the usually applied method of making pictures with digital cameras and comparing them visually or in Photoshop. Therefore the facilities of the Zeiss laboratory were used to measure and analyze a number of characteristics.
A photometric measurement of the T-stops gave theses results: 0.95/1.12; 1.4/1.44; 2/2.02; 2.8/2.8; 4/3.97; 5.6/5.41; 8/7.48 (engraved aperture/measured T-value). This listing proves that the apertures from 1:1.4 to 1:8 are very accurate, but the maximum aperture is not up to the claim and with a value of 1:1.12 the NHP is actually a 1:1.1 lens.
The vignetting at maximum aperture is about three stops and a bit higher than in the NX. In practice one can select in the Leica M9 manually the lens used and when one selects NX the internal software does reduce the edge fall-off. But is does not disappear. One has to accept that the relatively narrow bayonet throat of the Leica M in combination with the position of the exit pupil of the NHP do not match very well.
There is an unstoppable debate in the press and on the internet about the significance of scientific test results versus so-called practical test results. Some photographers/testers claim that they only trust their eyes and when the results produced with scientific methods do not correlate well with their personal experience they simply dismiss these facts (see for example among many others a recent article by Ctein on www.theonlinephotographer.com). In reality it is more complicated. The fact that you do not see or observe a certain phenomenon does not imply it does not exist. And what one individual does not note may be very evident for another observer. There is a troublous aspect in this discourse. Since the Renaissance humans have assumed that they are the true centers of the world and that the individual is the only yardstick that matters. So far, so good. Who would claim to know better that the Renaissance philosophers? The internet is swamped with reports by individuals who extrapolate individual experiences and results to general conclusions. There is nothing wrong with employing one's personal requirements as the ruler along which photographic products are to be positioned. This is everyone's personal decision. This approach becomes questionable when these rulers are used to make generalizations beyond the individual case.
My approach is different. I firmly believe that individual idiosyncrasies and limitations are misleading and can only be refuted or corrected by scientific analysis. Therefore the classical MTF analysis is still the best basic reference for the assessment of a lens. It may be the case that the MTF results cannot be replicated in practical photography, but then we are entering a totally different realm. The expertise of the photographer and the situation in which the pictures are made may have such a profound effect on the results that they cannot be reproduced by any other photographer. The laboratory results may seem academic, but they are neutral and objective within the boundaries of the inevitable tolerances. The MTF measurement has one shortcoming: you have always best and worst results when examining a lens, especially when astigmatism is present in a lens design. The NHP has a large amount of astigmatism and therefore the results must be described in two positions (maximum and minimum).
Here is the result for the 1:0.95 aperture. Focusing for the optimal position delivers results that are comparable with the NX, but remember that the NHP has a significantly smaller aperture. The worst position shows a major drop in performance. This is a classical problem. Many lenses have a sharpness plane that is curved and many lenses will focus their off-axis rays onto two distinctly separate curved surfaces (sagittal and tangential). The NHP is a very good example for this phenomenon. If the focus happens to fall on the best plane, the results (off-axis) are quite good, but when the focus is on the wrong plane, the result is quite bad. In most situations you focus on the centre and then the result off-axis is a mix between both extremes. The mixed results as described by various authors in internet reports can be explained by this aspect: the lens has a severe amount of astigmatism, a fact that is overlooked by every report: the limit of the value of a practical test has never been more clearly demonstrated.
Wide open, on axis and in an area extending about five millimeters from the centre the effect of astigmatism is not noticeable and here the NHP can score with good results that are close to what one can accomplish with the NX, that has more contrast and a slightly higher resolution, but has an aperture that is at least a half-stop wider and that is a significant difference.
Stopped down the performance does improve, but that is as expected and if you wish to use the lens at medium apertures there are better alternatives, like the Summilux-M 50 mm or the Apo-Summicron-M 50 mm (which by the way is more expensive than the NHP).
The NHP can be focused to 0.7 meters and the test results show that the closer you focus the more the contrast drops and the off-axis effects are visible. There is also a minor focus shift.The chromatic correction shows a strong undercorrection of the blue part of the spectrum. This is the usual design philosophy and this is responsible for the color fringes at the edges and several optical defects. The performance of the lens is quite sensitive to the focus position. A slight shift of 0.03 mm away from the ideal focus plane has profound effects on the image quality as can be seen in the graphs below. This characteristic may explain the varying reports on the internet about the NHP. Even when using a calibrated and accurately adjusted Leica M camera, it is not easy to find the optimum focus position without focus bracketing and a tripod. Trusting your expertise when focusing is not the best approach.
All the results reported in the previous paragraphs are lab results of the lens-as-is: it is the basic optical performance of the lens in question. A comparable range of tests was made with the lens attached to a Leica M9 body with the Image Engineering test environment. The results corroborate the previous ones. The graph below shows that the best and worst positions differ significantly. In particular the contrast for the 40 lp/mm is minimal to zero, even at the aperture of 1:1.4. This again supports the fact that the maximum aperture of the NHP is closer to 1:1.1 than 1:0.92: if you close the aperture a full stop, the improvement in quality should be more visible.
When the NHP is used for handheld practical shooting, it is a very pleasant lens to use with good performance, but not in same league as the NX, and landscape pictures can be disappointing when the effects of astigmatism are prominent. Used at maximum aperture one can get pictures that are comparable with the old Noctilux-M 1:1/50 mm. If you are looking for this quality the NHP is a good choice and probably cheaper than a second-hand Noctilux-M.
The tone of my report is rather critical, but one should realize that the lens itself is a very good design, but not well executed. The makers might rethink their options, but they must be highly commended for the initiative and daring to produce this lens.