Leica Noctilux-M 50mm f0.95 ASPH. , part 1 (May 18, 2009)

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.

Below: top row: Summarit, Summicron, Summilux
Bottom row: Summilux asph, Noctlilux, Noctilux asph

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.

2.5/50	2.0/50	1.4/50	1.4/50ASPH	1.0/50	0.95/50 ASPH	Specs
6	6	7	8	7	8	elements
4	4	5	5	6	5	groups
28	25.1	29.8	25.7	42.9	50.6	entrance pupil position
33	43.5	46.7	52.5	62	75.1	length
51.5	53	54.5	53.5	69	73	diameter
230	240	275	335	630	700	weight
50.1	52.3	51.7	51.6	52.4	52.3	true focal length
no	no	no	yes	no	yes	floating
0	0	0	1	0	2	aspherical surfaces

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.

Handling

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.

Overall performance

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.
Below is a series of test results for the centre portion of the lens. Noctilux asph compared to Summilux asph. The horizontal line shows the number of line pairs per image height (18mm). To help you translate these numbers to the familiar ones, here is a conversion table.
1400 = 78 line pairs per mm
1300 = 72 lp/mm (Nyquist limit
1200 = 67 lp/mm
800 = 44 lp/mm
600 = 33 lp/mm
400 = 22 lp/mm
200 = 11 lp/mm




From here the comparison is with the Summilux
Below NX at 1.4



Below SX at 1.4



Below NX at 2

Below SX at 2

Below NX at 2.8

Below SX at 2.8

Below NX at 4

Below SX at 4

Below NX at 5.6

Below SX at 5.6

Below NX at 8

Below SX at 8

Below NX at 11

Below SX at 11

Below NX at 16

Below SX at 16


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 superfast 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.
In the second part we will take an in-depth look at the wide open performance look with practical examples.

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