Leica Summilux-M 1.4/35mm ASPH. FLE, part 1 (May 17, 2010)

Introduction.

The new Summilux-M 1.4/35 ASPH. adds the floating element feature to the basic optical design of the 1994-edition of this very classical and popular lens. The f/1.4 aperture was married to the 35mm focal length in 1961, a first in those days when all other designs had a maximum aperture of f/1.5 or smaller. The 35mm focal length changed guard with the 50mm lens as the primary lens for Leica M users in the period from 1955 to 1965 when the style of documentary and human interest photography asked for a close encounter with the subject matter. The 35mm focal length is eminently suited for this visual frame because you can have a format-filling main subject encapsulated by a meaningful environmental statement. A wide aperture gave the opportunity to take pictures in low ambient light where claire-obscure pictorial composition was needed. The Summilux 1:1.4/35mm stayed in the catalogue till 1995, but in 1989 a new version with two aspherical surfaces was added to the range of Leica lenses. The production process was quite complicated and therefore expensive and a new somewhat simplified version was introduced in 1994. That version had one aspherical surface and was in production until recently and has now been superseded by the new SX35 FLE. The technology of floating elements where a whole group of lenses moves dynamically according to the distance setting was introduced in the M-line with the SX50 ASPH in 2004. Since that year, Leica has upgraded several high speed wide angle lenses to the FLE construct, notably the SX21, SX 24 and now the SX35. The main task of the FLE construct is to compensate for the loss of contrast that happens with stationary lens groups that have been optimized for longer distance photography. The spherical aberration (SA) which is always present in a lens is responsible for this behavior. In very high speed lenses this same aberration also causes a focus difference when stopping down. It is evident that the aperture stop and the focusing movement are not physically linked and the FLE construct cannot be used directly to battle the focus difference. But when a designer knows that (s)he has more design parameters, the overall design can be improved to correct more than one problem area. Below left: Summilux-M 1.4/35 ASPH, (1994) Below right: Summilux-M 1.4/35 ASPH. FLE (2010)

SX35 FLE

The physical dimensions have not changed much, the length is the same with 46mm and the front ring diameter is still E46. Weight is identical with 320 grams, but the internal lens mount has been substantially modified to make room for the floating element construction. Leica also changed the rangefinder cam of the focusing mount from the classical brass color to black. Romantically inclined Leica aficionados may deplore the fact that you now cannot see the individual adjustments, but with the computer controlled machining the black mount is at least equally precise. And the black version is more effective in evading reflections and flare. The focusing mount has a reduced diameter from 56mm to 53mm. In the slimming process the focusing level has not been dropped. The lens livery follows the style of the other lenses in the wide angle and standard focal length range. The distance settings on the focusing mount are changed a bit: the FLE version has 1; 1.2; 1.5; 2; 3; 7; infinity markings where the SX version has 1; 1.2; 1.5; 2; 3; 5; 10; infinity markings

Performance in the close range.

Leica states that the SX35 FLE is optically identical to the previous version. A comparison of lens design and MTF graphs clearly show the validity of this statement. Basically then the evaluation of the SX 35 ASPH. is equally vald for this lens, as long as you restrict yourself to the infinity setting or in practical terms to the object distances of 4 meters and longer. Many users of the 35mm focal length do operate in the distance range from 1 meter to 3 meters. This is the range where the wide angle lens can show its qualities. The two questions to answer are: is the focus shift reduced and is the close range performance improved. The short answer is to both questions is an unhesitating yes. But there is a caveat as is often the case. First the test results. The M9 was positioned at a distance of 1.35 meter for a test chart (the well-known Siemens star made by Image Engineering). I have noticed over a longer period that the print quality of the test chart is of paramount importance for the results. More about this in the S2 review. The IE charts are the best you can buy. The camera was put on a device where you can change the distance by millimeters. At first the camera was optimally focused (an act that demands patience and accuracy). Then there was a range of pictures made without changing the lens focus, but with the camera moved by 1 cm over a rage of 10 centimeters. This was done for both lenses, an SX with and without FLE. Two apertures were used: f/1.4 and f/2.8. See the table below.

distance

SX FLE 1.4
SLX FLE 2.8
SX 1.4
SX 2.8

0.05

16.6
18.3
19.1
17.4
0.04
18.5
18.8
20.2
17.6
0.03
19.6
19.6
20.9
18.1
0.02
20.7
20.3
20.9
19.4
0.01
21.7
21.2
20.6
20.2
0
21.8
21.8
19.9
20.8
-0.01
21.9
22.5
19.1
21.4
-0.02
21.4
22.5
18.4
21.9
-0.03
21.1
23.4
16.6
22
-0.04
20.2
23.4
15.6
22.4
-0.05
19.1
23
15.1
22.9


The number in the columns is a merit value. The higher the number the better the performance. The distance setting indicates that the 0.05 position is at the 1.40 meter and the -0.05 position is at the 1.30 meter setting. The first conclusion is that the SX FLE at f/1.4 has its best position at the indicated distance setting (plus/minus 0.01mm!). The SX has its best position slightly closer to the indicated setting. Remember that we are talking about differences of at most 2cm out of 135 cm or a percentage of 1.5%. This is really accurate! If we look at the optimum setting wide open the FLE has a value of 21.9 where the SX brings 20.9 on the scale: the claim that the wide open performance in close up range has been improved can be validated. For the focus shift the conclusion is clear: SX FLE at f/2.8 keeps its performance at nominal distance setting and there is a small focus shift to the front over a total distance of 3 cm, which is as expected. The SX on the other hand has a focus shift of 5 cm, almost twice the range of the FLE version. This is a big improvement. Again as a percentage it is 3% and we should put this in perspective: a slight horizontal movement of the body during focusing/shutter release creates a bigger difference. Remember too that we are talking about a lab setting where great care has been taken to get the optimum results. In general work, even on tripod, the differences will be smaller. But the experimental results indicate that the focus shift is substantially removed and that the performance wide open and stopped down has improved in the close range domain from 1 meter to 3 meters. It depends on the quality of your own work if and how good you see the differences, but the improvements are real and visible.

Overall performance.


Wide open the SX FLE delivers a clean and crisp image with excellent definition of very small details.
See below a small part of the full image taken wide open at close range.





The corners and edges are of lower contrast and details are depicted with softness. At f/2.8 you see the improvement based on better control of the focus shift. The graph of the 40 lp/mm has improved contrast at the center of the image, compared to the SX version. At f/5.6 the FLE holds the lead and now the performance exceeds the possibilities of the CCD capture element of the M9/M8.

Below: MTF of SX35 ASPH



Below MYF graph of SX35FLE


The lens does improve when stopping down: the increase in overall contrast gives images a clean and transparent look and fine detail is seen with crisp outlines, emphasizing the excellent life-like representation of three dimensional objects. Generally one could remark that the optical and mechanical improvements are best seen when you use the digital workflow. When film is employed in the M3/MP range the differences are a bit masked by the emulsion thickness, but more visible when using the current mono-dispersal emulsions.
There is some coma visible at wider apertures at the longer distance settings. The effect is quite small, but visible. Secondary reflections and flare are still present under adverse situations. It is less evident than with the SX design. It this domain Leica has made good progress and the delay in the production has partly been caused by final improvements in the flare reduction by coating technology.
Bokeh is a bit unruly in the background with specular highlights. On the other hand the unsharpness gradient is wide open and at close range very pleasing.



On the other hand the unsharpness gradient is wide open and at close range very pleasing.



Flare is visible when you force the lens to capture very strong lights in oblique position.





Night pictures wide open show excellent contrast in the shadow areas and good containment of high-light areas.



Conclusion.


The new SX35FLE is a definite improvement over its predecessor. But the main advantages are to be found in the focusing range from 1 meter to 3 or even 4 meters. There the performance gain is visible and to be appreciated. If you already own an SX35 ASPH and work mainly at larger distances, you might not see much improvement. For closer range subjects it is a matter of critical distinction. If you did not find faults with the SX35ASPH image quality or do not need the ultimate in quality, the urge for an upgrade is less pronounced. If you own a non-asph 1.4/35 or even an 2/35ASPH and want more punch wide open and up to f/4, the new SX35FLE is a very tempting proposition.