Leica Super-Elmar-M 18mm f3.8 ASPH
It is a matter of definition and taste where one will draw the distinction between wide angle and super wide angle and extreme wide angle lenses. It is safe to note that focal lengths wider than 21mm (for 35mm format) are considered super wide angle and that focal lengths wider than 15mm are designated as extreme wide angle lenses. It is also interesting to observe that in the wide angle corner of optical design the focal length differ by a mere millimeter, while the telelens designs differ by a much larger amount. Standard lenses can be found in the 50mm, 52mm and 55mm range. The wide angle lenses can be listed by a much tighter scheme: we have 12mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm. One reason for these finely calibrated steps is the mounting optical challenge when you wish to push the limit of wide angle designs and another reason is the fact that a millimeter difference in focal length of wide angle lenses has a much greater visual impact on the resulting photograph. The 18mm focal length is for the Leica M lens line not a first: the Tri-Elmar-M 16-18-21 offered this focal length already. As a fixed focal length the SEM18 is a first for Leica, introduced just in time after the Zeiss ZM 18mm.
In the late sixties of the previous century Zeiss introduced the 4/18mm lens for the Contarex system. Geoffrey Crawley was quite impressed by the design and commented that optical progress allowed the construction of such a lens with very good quality, a feat that had been virtually impossible till that moment. That was forty years ago. Current design programs and optical glass quality make the creation of such a design much simpler.
The 18mm focal length has one intriguing characteristic. The horizontal angle is exactly 90 degrees and can cover a space with geometric precision. For this wide angle to be useful three demands must be met: good definition, very low distortion and absence of vignetting. The last requirement is less demanding in this age of post-processing software, but for photographers who value film and/or do not want to get bogged down in computer manipulations, it is still a valuable parameter.
Currently Leica offers two lens designs in the 3.8 family, one with 24mm focal length and one with 18mm focal length. Both lenses share the by now familiar mount design. Both have 8 lens elements and the last group of 5 elements is quite similar. A Leica first is the aspherical lens element with both surfaces a-spherical.
The Leica text writers should try to stay on track when describing the lens characteristics. The distortion of the 24mm is 1% and the writer notes that is hardly noticeable. The distortion of the 18mm is at its maximum 1.8% and now the writer notes that this is virtually undetectable to the human eye.
The MTF graphs of the 24 and 18mm are quite comparable. Especially wide open there is not much difference. The same conclusion holds for the f/8 aperture. The main distraction is the 5.6 aperture, which in the case of the 24 is clearly better. In the case of the 24mm the lines for the sagittal and tangential direction are very close and for the 18mm there is a wider divergence, especially at the definition of the finer details. In practice this behavior translates into a less crisp definition of the edges of fine detail.
The SEM18 is constructed with the new standard mount of Leica M lenses. It is a clean and stylish design, and offers a very smooth and firm handling. The lettering no longer follows the hard edged digital style but the round forms of the classical Leica period.
The design of the mount is now based on the approach that components should be manufactured with the necessary tolerances of the parts machined before assembly takes place. This limits the amount of manual adjustments and part selection and ensures a consistent high level of quality.
The finder has frame lines for the 35mm format and the 1.33 crop factor. The view tough the finder is very clear and lacks the tunnel vision of previous designs. The provision of two sets of frame lines asks for some concentration when framing the scene.
Super wide angle lenses are supposed to be used for the wider angle of view they provide. For this type of lenses the three overriding quality criteria are drawing, definition and vignetting. I used the M7 loaded with the new Spur Copex microfilm in combination with the new DSX developer. Having to use such a potent film is already a clear signal for the quality that can be expected.
At full aperture (f/3.8) the contrast is medium/high over the whole frame with crisp rendition of extremely fine detail over a large central portion of the negative (a circle with a diameter of about 20mm). In the outer zones the definition of very fine detail drops visibly, but overall contrast stays medium to high.
At f/5.6 overall contrast improves to high and the circle of good definition now extends to the edges of the image, with the far corners still lagging a bit behind. The quality in the corners is in itself very good and the whole frame can be used with confidence when high performance imagery is required.
Below a small part at the edge of the frame: at f/3.8 and at f/5.6 (far below)
Most current wide angle lenses designed by Leica follow the same correction approach for distortion: the distortion curve bulges outward in the 2/3 zone and returns to zero in the edges. This option delivers a visually pleasing effect. The lines do not recede out of the edges which is visually disturbing. In most situations the distortion is hardly visible, but in the situations where straight lines are being recorded in the outer zones of the frame the phenomenon is detectible. The fact that you really have to search for distortion effects is a measure of the high level of correction. When using the SEM18 on the M8(.2) the distortion might be a bit more visible. The 18mm focal length is quite critical and when you wish to analyze the distortion you need a tripod with a spirit level to ensure correct positioning of the camera. Even a slight disrupting of the balance becomes visible as receding lines. One should not become over-anxious here. The receding perspective can be used with good creative results.
Film is quite good in covering up small differences in luminance. At medium distances the vignetting is detectible as a slightly brighter area in the middle of the frame on the negative, but in the print this disappears. With normal exposure the vignetting can be neglected, but with under-exposure a darkening in the corners may be visible. As with distortion the phenomenon is not really visible in most picture taking situations and certainly not a big issue. The M8 software was not yet upgraded to this lens and the vignetting reduction was not active. Therefore I will not yet comment on light fall off with the M8 series of cameras.
There is often a controversy about vignetting because some users report a strong level of vignetting while others are not bothered by it. Scenes with even illumination and with textures with even density will show a brighter central area with gradual fall off to the corners. But the eye will adjust to these differences quite easily.
Performance: close up.
An 18mm lens will not be used predominantly for close up pictures. Even so, the image quality at 0.7 meters is excellent even wide open. Very fine detail is crisply recorded over a major part of the picture frame. To get a good performance across the frame one must ensure a parallel alignment with the subject plane. At f/8 the microcontrast is increased and the performance at the edges is visibly improved.
Wide open there is strong vignetting, but only visible in the extreme corners.
Below I will look at flare, and look at the issue of the hyper focal distance. It is assumed and also promoted that a snapshot setting will allow for good sharpness over the whole depth of field as the circle of confusion will cover for any unsharpness caused by a focusing error. I have my doubts, but this will be covered in detail in the second part.
Lens diagrams and MTF graphs can be found at the Leica camera site.
The SEM 18 is a true workhorse lens, it lacks the glamorous attributes of a Noctilux or the historical pedigree of the Summicron 50mm. It is also one of the very few lenses without flaws and can be truly referred to as a masterpiece of design. It's slender dimensions belie its performance.
In the first part I noted the excellent general qualities of contrast, field of view, definition and tonal reproduction on film. On the M8 series the crop factor does reduce the useable angle of view to that of a 24mm.
This is a lens that can be used without any reservation at all apertures and distances and under all circumstances. Every time it will bring the best possible results.
Flare is almost non-existent. You really have to trick the lens to create flare. The hyperfocal distance.
With a lens with such inherent depth of field focusing would not be necessary even wide open.
This statement depends a little on distance. At a distance of one meter there is a visible difference in sharpness between the spot on focus and the hyperfocal distance. At moderate distances (around three to seven meters) the difference in sharpness is negligible. It is a logical conclusion that stopping down to smaller apertures will increase the depth of field, but also increases the unsharpness due to the slower shutter speed. The final trade off must be made by the user.
The Leica SEM 18 is a very fine lens that functions flawlessly in almost any situation where the lens is asked to perform. The images are very natural, hardly without distortion and with excellent definition from centre to edge. It is very close to the sibling lens, the Elmar-M 3.8/24mm ASPH in characteristics and makes a good pair.
The even and homogeneous performance does easily forget that this is a true 18mm lens with a 90 degrees horizontal field of view. It is not a general purpose lens, but one that really challenges the creative capabilities of the photographer. The lens is able to force a new visual awareness on the user. After mastering the lens characteristics you will use the lens more often than you could have anticipated. I myself used the lens more often than I had intended to do. The perspective is both fun and challenging with an outstandingly good imagery.
Photographers with a historical background will remember with fondness the Super-Angulon lenses f4 and f3.4. The SEM is very close in general profile but with a much higher performance. at a wider angle of view.