Leica Summilux-M 1:1.4//21mm ASPH. and 1:1.4/24mm ASPH. , part 2 (January 25, 2009)
Introduction
It is standard procedure for most high speed lenses with apertures of 1:1.4 and more that the wider apertures have to be used with some consideration for the performance characteristics at full aperture. In most cases, stopping down does improve the quality markedly. Specifically overall contrast, definition and the crisp rendition of quite fine detail get visibly better when you move from full aperture to smaller stops. The classical fingerprint of the high-speed lens with a performance jump from full aperture to one or two stops smaller and then a gradual improvement to the optimum diaphragm is nowadays less prominent. Most current designs have a good overall contrast wide open, but lack some bite when recording finer details. A high speed lens cannot be optimized for the whole spectrum of demands one would list for a universal lens: uniform performance over the whole image field, at all distances and for every aperture. At shorter distances the image quality deteriorates, but is often explained with the fact that the high speed lens is for reportage use. For a medium tele-lens this argument may be appropriate, but a wide angle lens is often used at quite close distances.
Below SX21
Below SX24
There is a widespread tendency to characterize wide angle lenses as useful for landscapes and architecture and for capturing much of a scene in a confined environment. In fact one cold argue for the opposite position. Wide angle lenses are preferable whenever you need a dramatic composition with the main object prominently in the foreground and the background enveloping around the central object for contrast or substance,
In such cases the quality at closer distances must be high, even at full aperture, in order to make good use of the unsharpness gradient.
The new Summilux designs for the focal lengths of 21mm and 24mm follow the standard set by the Summilux 50mm with floating elements and aspherical surfaces.
Film Orthopan
A full assessment of the performance of these lenses requires the use of film in order to study the image quality at the outer zones and edges. In this case I used the M7 body, loaded with Spur Orthopan film, exposed at EI 20 and developed in Spur Nanospeed. This choice in itself is already a sign of the potency of these two new lenses. Comparison tests with the M8 body indicated that the limit of resolution of the sensor would be reached before the optimum lens performance could be displayed. All tests were done on tripod and in low contrast situations to establish a bottom line. Specifically in sulky weather the demands on the quality of the lens does increase. It is no big problem to have good contrast in sunny weather.
SX21: definition
At full aperture very fine detail is crisply rendered over a large part of the image frame. Edge contrast of the major subject outlines is high. Towards the edges and corners of the frame fine detail is becoming fuzzy, but the outlines hold on with a good edge contrast.
Stopping down improves the outer areas of the image visibly and at 1:4 the optimum is already reached with outstandingly good definition over most of the image area, but the edges lag behind. Stopping down to smaller apertures (1:11) does improve the edges of the image to match the quality in the center. A small softness in the rendition of very fine detail can be detected, but you really must be focused on these details at big enlargements.
In practical use, you will not notice big differences between the wide open performance and stopped down to 1:11. This behavior is exemplary and sets a new standard for the performance level of high speed very wide angle lenses. Many high speed lenses do improve on stopping down, simply by reduction of the flare factor. The SX behavior is also a sign that flare is very well controlled.
SX21: vignetting
At full aperture there is a visible darkening at the edges of the frame. Stopping down to 1:4 removes most of the vignetting. It is really difficult to give useful information about vignetting as the occurrence of vignetting depends on several factors: the exposure itself, the characteristics of the scene, the characteristics of film and so on. In most circumstances the vignetting of the SX21 at wider apertures is hardly obtrusive and only occasionally a real nuisance. The vignetting you see on negative will be partly compensated in the darkroom. On the M8, the software (when the lens detection option is activated) does a good job in at least reducing the darkening to quite acceptable proportions. The published curves which show vignetting values of 2 stops are correct, but this amount of darkening is only visible at the extreme edges.
Vignetting is stronger when making close up pictures. Wide open you see a brighter area in the middle of the picture. At smaller apertures the density is homogeneously distributed over the whole image area.
SX24: definition and vignetting
The publication of MTF graphs is a fine idea when one wishes to study and compare lenses in detail. It is easy however, to fall into the trap of attaching too much value to small differences. The MTF graph of the SX24 wide open looks not as good as the SX21 and extrapolating from theory to practice would imply a softer definition and lower contrast at the 1.4 aperture. Below you will find two extremely small sections from the whole negative, absolutely not manipulated: these are negatives as scanned with identical settings. The slightly higher softness of the image is just visible. The difference is not that big that the choice between either lens should be based on the wide open performance.At full aperture very fine detail is clearly rendered over a very large part of the image frame. Edge contrast of the major subject outlines is medium to high. The edges and corners of the frame hold fine detail over a wider area than the SX21, partly due to lower level of vignetting.
Below section of 21mm at 1.4
Below section 24mm at 1.4
NOTE: The small differences in contrast as described in the text are lost in the reproduction on this website because of the 72 p/inch resolution.
Stopping down to 1:4 brings the contrast and detail definition to levels equal to the SX21 at the same apertures and due to the slightly larger magnification (at the same distance of course) slightly finer detail is just detectible. Stopping down to 1: 11 improves the edges and corners as usual. Compared to the SX21, the overall image quality is now very homogeneous over the full image frame from 1: 4 to 1:11. Vignetting is slightly higher in the SX24 images, but disappears after stopping down to 5.6. A slight corner darkening will however be visible even at 1:11. (same with the SX21).
The comparison with the Elmar-M 3.8/24mm asph. at apertures from 3.8 to 8 is informative: At 1:4 the Elmar shows identical definition in the image center, but slightly crisper definition in the outer zones till the edges and far corners. Vignetting is also lower. At smaller apertures this fingerprint holds and the Elmar has just a fraction better definition and edge contrast than the SX24.
In the not so distant past, one could hardly compare with decency two lenses with apertures so widely different from 1.4 to 3.8 and only detect small differences. In is certainly a tribute to the Leica designers that the new 1.4 designs can be approached as fully normal lenses without making reservations.
SX21: distortion
Distortion, interpreted as the curvature of straight lines at the outer zones of the image area, is visible, but the effect is quite moderate for a 21mm high speed lens. As with the aspect of vignetting, the distortion is more or less visible and disturbing depending on the scene. The picture here has strong geometrical lines (rows of stones) and in this case distortion (seen in the curvature at the top edge of the image) is visible, but not obtrusive. On the M8 this effect is much less an issue, due to the reduction of the capture area. With ‘honest’ film one has to be more attentive.
There is one other type of curvature that is prominent with wide angle lenses. When making pictures at closer distances of flat surfaces, like walls, there is the subtle spheroidal effect that the center part of the mage seems to push forward and the rest of the image seems to recede. This is natural for this type of lenses and not a defect.
SX24: distortion
Distortion is just visible in the corners and on he same level as the SX24. The Elmar 24 has the lowest level of distortion. All three lenses exhibit a low level of distortion that is certainly visible, but becomes never objectionable.
SX21: close up performance
Wide open very fine detail is rendered clearly over the full picture area, but with a slight veil of softness. The image has not the crispness of the pictures made at medium distances, but is fully usable even at quite large enlargements. The effect of the floating element is clearly present: without this device the image would be much softer. The residual smoothness is a sign that a floating element is no wonder oil, but a very effective tool to improve close up performance significantly. Stopping down does improve the crispness of the rendition but the gain is modest, but of practical importance. The fact that you can discuss the performance of a 1.4/21mm lens at a distance of 70cm wide open and stopped down without seeing a big difference in definition and contrast is remarkable.SX24; close up performance
Wide open very fine detail is rendered clearly over the full picture area, but with a trace of softness. At smaller apertures the fine details are rendered quite crisply and one can recommend using the close focus range without reservation, form 1.4 to 16.
The comparison with the Elmar 24 at the same close up distance shows that the Elmar at 1:4 has a slightly crisper definition of the very small details. This small advantage holds over the aperture range from 3.8 to 8.
Below: SX 24 close
Below E 24 close
The floating element in the SX24 (and 21) does not necessary improve the image quality at close distances. This is not the role of the element. The point is this: the correction of a lens is normally done for rays that enter the lens more or less as parallel rays. And the aberration correction is derived form this condition. At closer distances the rays are inclined to follow quite different paths and the more so when the aperture and the angle of view get wider. A designer needs to find a balance between these two extreme positions and often the compromise is set to favor the longer distances. The close up then drops in performance. The floating element is used to compensate this compromise and create good performance even in a high speed lens at very close distances. The floating element is used to get the best quality that you can get with a comparable lens at normal apertures. This comparison shows that the floating element in the SX24 functions very well.
SX21 and SX24: at infinity
“Infinity” is a somewhat ambiguous concept. True infinity is physically impossible, but the distance to the moon from earth is definitively close to practical infinity. In optical handbooks ‘infinity’ is defined as that distance of the light source to the lens where the incoming light rays from that point are parallel. In photographic handbooks the concept of infinity and circle of confusion are related and the following rule of thumb can be found: any distance beyond ‘x’ is interpreted as infinity because then the CoC is so small that one can speak of an infinite distance. ‘x’ = (the square of the focal length) divided by (the product of CoC and aperture). For the SX 21 at 1.4 this formula amounts to a distance of 18.5 meter. Any distance beyond that is infinitely far away. As a very loose approximation one can also work with the 1000 times the focal length rule. Landscape pictures are however often taken when the horizon can be at several kilometers distance. When you take a picture of an object at such a distance (a skyline or the rim of a mountain), different considerations must be weighted. When you enlarge such a picture, it is not uncommon to find the details lacking or being unsharp. One could assume that the lens is not correctly set at infinity. Assume you take a picture of a scene at a distance of 200 meters. Then the magnification is roughly 1/9500. An object with a height of ten meters will be reduced on the negative to a size of 1mm! The sharpness impression of the outlines of the object are defined by the depth of field as defined by the CoC diameter and the true location of the plane of sharpness at the infinity position of the lens mount.
It is unlikely that you are going to take landscape photo’s at very large distances with the SX21 or the SX24 at full aperture. For my infinity tests I used a distance of 100 meters. Wide open the objects at that far distance were small, but clearly rendered. The grain structure of the emulsion started to break up the edges of the objects, but no trace of fuzziness. Stopping down did tighten the grain clumps and this did improve the definition of outlines. Both lenses perform commendably at infinity settings. A check with the Elmar 24 brings identical results.
SX21 and SX24: unsharpness behavior and perspective.
Wide angle lenses offer some peculiar characteristics, that one needs to know for effective use. The first characteristic is the rapidly shrinking size of objects from near to far. This behavior is an optical illusion, because the viewing angle is different from the picture taking angle. It is often assumed that a change of focal length will alter the perspective. This is not true. Look at the following calculations.
A 50mm focused at a distance of 1.5 meters will reduce the object to a size 1/30 of the original size and at 5 meters the object will be shrunk to about 1/100: a ratio of 1:3.3
A 24mm lens focused at the same distances will have size reductions of 1/60 and 1/200 and a 21mm lens will give reductions of 1/66 and 1/230. Here the same ratio occurs. If we enlarge a section of the negative of the 21mm lens to the same size as the negative of the 50mm lens, the sizes of the two objects at 1.5 m and at 5 m are identical. The imaginary pictures have been made at the same distance of course. If you now change the distance in order to maintain the size of the the main subject, you need to set the distance with the 21mm to 0.75 meters to get a reduction of 1/30. Now the object at the distance of 5 meters is again reduced to 1/230 and the relative sizes do differ. The perspective has apparently changed. Would you be able to look at the negative taken with the 21mm as close as 5cm then the perspective would be ‘normal’ again.
The second characteristic of the wide angle lens is the extended depth of field, a fact that allows for some relaxation in the focus accuracy (the snapshot position!), but adds the impossibility of isolating the main subject from the background and foreground.
below SX 21 at 1.4
Below: SX24 at 1.4
The SX 21 and 24 offer interesting options for isolation the main subject when the lenses are used wide open. See the examples that show that this aspect is indeed one of the important characteristics of these lenses. keep in mind that the effects of isolation, even at 1.4, do diminish when the taking distance increases beyond 3 meters.
See picture below. SX21 at 1.4
The unsharpness gradient wide open allows for good isolation of the main subject. Stopped down to 5.6 shows the increased depth of field. Here the Sx21 is used as example. Left at 1.4, right at 5.6
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SX21 and SX24: veiling glare and secondary reflections
The SX21 has excellent control of secondary reflections. The picture below (sun obliquely into the lens) shows only one reflection close to the light source. Note however, that the branches loose contrast and blackness, a clear sign that there is some veiling glare. This picture is with the lens wide open. (SX21).
Stopping down does improve the image significantly, but does not remove the effect completely.
below is a picture that is in itself not related to the lenses discussed here, but is a defect of the sensor.
The green bar in the picture (small section of the full scene) is a wrong nterpolation of the software (I assume) of the radiation pattern of the bright light source. It does not happen often, but is does occur occasionally.
The SX24 under extreme situation scan show a secondary reflection, but has a better control of veiling glare at wide apertures,a s can be seen in the dark branches of the tree.
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Both lenses perform very well in this critical discipline and behave as well as lenses with longer focal length and the same high speed. Perfect they are not, but there are limits to what a designer can accomplish and we should also take into consideration.
Conclusions.
The SX21 delivers outstandingly good imagery and when one takes into account the high speed of the lens, it is close to superb. You can always find aspects that can be criticized, but criticism because of criticism is not the best approach. And this lens can hardly be faulted. One would wish somewhat more definition in the outer zones at the wider apertures, but to restate the position, the wider apertures are not meant to be used for architecture. For documentary work and the art-snapshot the critical definition over most of the frame and the fine unsharpness gradient are a big benefit. The lens hood is a must however and should be always in position.The performance of the SX24 is very even over the whole image area, but wide open the overall contrast is slightly less good than what we have in the SX21. One should not over-emphasize this behavior, as it can be compensated quite easily with film (steeper gradation and selection of paper grades) and with post processing in the M8 domain. The SX24 compares favorably with the E24. This lens (the E24) delivers overall outstandingly good quality and it is an achievement of first order that the SX24 with the high speed of 1.4 can be compared without problems with a 24mm lens of more modest speed.
The choice between the SX21 and SX24 can be made solely on intended use and artistic considerations. The SX24 is the more compact lens, and the angle of view is very pleasant for the film domain where you can use the full potential. On the M8, the 24 gets cropped to a viewing angle of 32mm and is close to the classical Leica focal length of 35mm. In this respect the new SX 1.4/24mm has better performance than the SX1.4/35. The SX21 on the film loading Leica cameras brings a new experience in the wide angle domain and is really a joy to use. On the M8 the practical angle of view is 28mm. For reportage, documentary, snapshots and location photography for fashion and portraits this is quite often appropriate. In these situations the high speed allows a new type of imagery and combined with the compositional advantages of the wide angle, the photographer is to blame if the pictures are not visually pleasing and arresting.
A nice combination would be the SX21 and the E24. Then you can use the full range of options on film and with the M8. The other way around would be the SX24 and the very compact Zeiss ZM 4.5/21mm. f you prefer to stay into the Leica scuderia the Elmarit 21 might be a consideration, or the Tri-Elmar 16-18-21.