All SLR lenses are Coke® bottles, right?

Click to enlarge. The eyes are the focus point. What lens took this?

The advent of digital photography has made a couple of things clear: (1) many pros did not have so much talent as ability to overcome barriers to entry and (2) much of what you were told about lens quality – in terms of SLR versus rangefinder – was (or is now) untrue. This second point bears some examination.

What is the state of play on SLR vs rangefinder lens quality? The perception of SLR versus rangefinder lenses was developed when both shot on film, and there has been a major reversal of fortunes. Film was not sensitive to the angle of incidence of light coming from the back of the lens, and because rangefinders did not have mirrors, lens designers could make symmetrical lenses whose rear elements might sit just a few millimeters from the film surface. This knocked out distortion, incurred a little bit of vignetting (which was largely absorbed by the latitude of negative film, and resulted in a compact package.

SLR lenses, on the other hand, had to design around mirrors. So lenses under 50mm generally had to start with a longer focal length and then compensate it down by introducing a negative element in the front. This retrofocus arrangement generally compromised distortion and sharpness slightly, but it produced a good enough result that SLRs were able to exterminate rangefinders as mainstream cameras. But today, when the imaging surface is a flat sensor with a Bayer pattern, chromatic aberration, angle of incidence, color shift, and vignetting became big issues for traditional rangefinder lens designs. Even Leica’s very expensive wide-angle rangefinder lenses, on Leica’s very expensive bodies, were now capable of returning disappointing results in terms of color shifts and vignetting.

The goal today is sometimes called telecentricity, which is commonly understood to be the situation where light rays hit the sensor parallel to the lens axis. It is still achieved by retrofocus designs. It is telling that many Leica and mirrorless wide angles that avoid color shift and vignetting are creeping up in size to SLR lenses. Witness Leica’s fast wide-angle lenses, which are quite large – especially when you compare aperture to aperture. A 21/3.4 Super Elmar has a 46mm front thread; the 21/2.8 Elmarit-M has 60mm, which is only a hair smaller than a 20mm f/2.8D Nikkor (at 62mm). But nowhere is this phenomenon more stark than in Fuji XF lenses, where the register is shorter, lenses cover an APS-C image circle (much smaller than a 35mm camera’s) nor have to clear a mirror, and the lenses yet are 80-90% as large as SLR versions of the same.

Why do SLR lenses meet our expectation bias? In one sense, it is fair to complain about the quality of SLR lenses because the end result is not what we want – and measured as a system, they indeed underperform. But in an era where SLR lenses are being adapted for use in other things, it is fair to deconstruct what part of this is fairly attributed to parts of the system we are no longer using, such as the traditional SLR itself. And let’s be clear about this: until the advent of mirrorless cameras, the SLR (or DSLR) was the only way to achieve perfect, parallax-free framing and to reliably focus long telephotos and macro lenses.

— Focusing wide-open, shooting stopped-down. All SLR lenses are focused wide-open, which makes focusing accuracy vulnerable to focus shift. This phenomenon, which comes with spherical aberration and “good bokeh,” means that a lens might be perfectly focused at a wide aperture but back-focused when the aperture stops down for shooting. This same thing afflicts both rangefinders and SLRs, only in rangefinders, it is written off as “focus shift” and in SLRs, it is called “being a poor performer.” Aspherics and floating elements help mitigate this – and both are in play on modern lenses of all types.

— Suboptimal focusing screens. You can’t win with a single screen on an SLR. The original SLR focusing screen, a plain ground glass, excelled at focusing telephoto lenses because as the focal length increased, so did the magnification of the subject that the photographer sought to focus. But this screen was dim in the corners and sometimes dim, period. It also failed with wide-angle lenses, where the details critical to focus were actually reduced. Over time, SLRs developed focusing aids like split-image center reticles (actually tiny rangefinders). They also introduced fresnel surfaces to brighten the corners. These made it simpler to focus lenses 50mm and down, but they degraded the ability to accurately focuses lenses 85mm and longer.

— Small viewfinder magnification. A key constraint of camera viewfinder systems is that eye point and magnification are in direct opposition. In practical terms, this means that to be able to see the whole picture through a reasonably-sized viewfinder, especially while wearing eyeglasses, the picture must be reduced. This degrades the focusing abilities of every SLR focusing screen.

— Taste-making. The problem with publications like Popular Photography (and now sites like DxOMark) is that they focus the user’s attention on tests that bear little or no necessary connection to real life.The old-school photo magazines paid little attention to rangefinder lenses, so the tests of SLR lenses were generally focused on the relative merits at huge enlargement factors, and not surprisingly, among SLR lenses, the results favored more expensive glass (the larger advertising budgets of the major companies is always suspicious as well). This did not affect the sales of SLR lenses in general (because at the time no one really liked rangefinders), but it did lead to a perception that anything other than a name-brand Canon, Nikon, Pentax, Minolta, or Konica was garbage. This was an inaccurate and unfortunate perception for three reasons: (1)  Cosina, Tokina, and Sigma were making some of the major brands’ lenses under contract; (2) some of the aftermarket lenses performed adequately for the purpose; and (3) the blanket perceptions about these products, particularly third-party lenses, has landed literally millions of completely usable (if not in some cases very good) lenses in landfills.

— Leica people. Yes, we said it. For all of the doctors, economists, attorneys, CPAs, and engineers who own these and similar rangefinder cameras, there is a widespread misperception that MTF figures for SLR lenses – like home run statistics for Japanese baseball – need some kind of implicit adjustment downward to be comparable to MTF for rangefinder lenses. Not so. MTF is MTF, and it is measured in standardized procedures that do neither the camera body nor care about the lens design itself. It is of some note, conversely, that Leica’s presentation of 5lp/mm (a largely obsolete measure relevant primarily to optical prints) leads to an impression that Leica’s MTF numbers are “higher and flatter” than comparable brands.

Turning the world on its head. Two things changed the picture (so to speak), and quite radically.

— First becoming last. As noted above, he advent of 24x36mm (“full-frame”) digital cameras has exposed just how poorly some traditional rangefinder lenses perform when they project images onto flat sensors. That negative effects are minimized on smaller digital RF and mirrorless platforms (because those corners are effectively cut out of the picture) is immaterial; the only compelling thing about using rangefinder lenses on another camera is killer wides. And frankly, native APS-C lenses – because they are designed correctly for digital sensors – crush adapted rangefinder wides.

— The closed circuit. One of the things that makes mirrorless cameras really, really good is that their autofocus systems can gauge focus from the sensor itself. But this benefit – which bypasses all of the focusing infirmities of SLRs. But the same advantages obtain when attaching manual focus lenses. Not only can the user see the image exactly as resolved by the sensor; he or she can see it at greater magnification or with focus peaking. Getting virtually any lens on to any body never seems to cost more than $30, and there is now plenty of opportunity for exploration on an epic scale.

How do SLR lenses do on digital bodies?  The answer is, “it depends on the lens.” The first place to start is the adapter. It needs to be plane-parallel and to have the correct register. Many adapters are off-kilter and are cut short to “assure” infinity focus. They will need to be shimmed sometimes to achieve correct infinity focus (if you want to scale-focus wide-angle lenses). Once you get past that, this is what you can expect. Over the next few posts, we will explore some favorites, but we will spill the beans on a few “sleeper” lenses here. Caution: be careful with M42 (Pentax Screw Mount) lenses with automatic apertures – you may need to disconnect the stop-down pin to get to shooting aperture.

— Wide angles (<35mm). Because these lenses have a palpable focus point wide-open, an EVF, either at magnification or with focus peaking, is the best way to focus these. Consider also that if you are shooting traditional rangefinder wides and actually focusing them, you have to look first in the camera’s viewfinder/rangefinder window, then switch to an external finder. An EVF kills both birds with one stone (or look). Wide-angle lenses will generally perform best close-up, where errors in infinity register will have the least effect (and you should never be aiming for infinity with shorter than a 35mm lens anyway – since subject details are getting too small to give any impression of sharpness). If your thing is close-up, wide-open shots, the Vivitar 20mm f/3.8 Auto is one of the best and cheapest things going. The header picture for this article is shot with it, wide-open on an M typ 240 (which is way more resolution than any historic 35mm-format lens was ever made to handle). Reasonably low distortion (-5 on Lightroom, if you have any straight lines in the shot), high sharpness (click to get it full-size, then blow it up to check out the eyes, which are the focus point), nice bokeh, and reasonable vignetting. Vivitar lenses should not be ignored; this was a company that often employed its own lens designers in the U.S. and produced many manual focus lenses that were quite good (disregard the autofocus products and recent-vintage manual focus lenses, which can be pretty bad). Did we mention that it often costs less than $60? The Tokina RMS 17mm f/3.5 manual focus lens is also pretty good, though it often shows up a bit overpriced. Adapted wide-angles are not as compelling on APS-C cameras – because they become slowish, semi-wide lenses with huge form factors.

— Normal lenses (50mm-60mm). This is the place where there is not much point to adapting lenses – except on APS-C cameras, where these behave like fast-ish short telephotos. The lens that came with your camera is going to outperform an adapted lens – and focus both faster and more accurately. Plus you already own it. One exception is in super-speed (f≥1.2) normal lenses, which become the equivalent of a 75/1.2 on an APS-C camera or remain an awesome 50/1.2 on your Leica M or Sony A7. If Leica users need EVF to accurately focus the $10K 50/1 Noctilux, you shouldn’t feel bad about using one to focus your 1970s Nikkor. The nice thing about 50/1.2 lenses and 57/1.2 lenses is that they were every SLR manufacturer’s showpiece lens; the optics are almost always great. The other use case for adapted normals is for lenses with “character,” such as Tessars and Sonnars. The Soviet Industar 50-2 (50mm f/3.5) and -61 (f/2.0) (both 50mm Tessar, M42 SLR mount) fit this bill.

— Telephoto lenses (≥75mm). Assuming that you can get a high enough shutter speed to use these (you generally want the reciprocal of 2x the focal length or faster), this is where things get fun. SLR telephotos are often a stop or two faster than rangefinder telephotos, and they often have slightly lower contrast wide-open (which was never historically a problem, since for most of history people used these lenses to shoot high-contrast, low-light pictures). Focusing is less challenging due to the higher magnification, and with many of these, focus peaking suffices (magnification would be absurd). From a quality perspective, even cheap telephotos work really well. Here, we would jokingly tell you to “go big or go home.” A worthwhile lens to try is the Konica Hexanon AR 135mm f/3.2. This is the best of Konica’s SLR 135s, it is the cheapest ($50 on Ebay), and it focuses down to a meter. Make sure it’s the 3.2 and not the 3.5 or 2.5. The Soviet Helios-40-2 (85/1.5) is a cult favorite, but there is no argument that it is cheap at $300-400 these days. It was fun for a C-note, but those days are over. The Soviet  Jupiter-9 (85/2) (Sonnar, M42 SLR mount) is also a solid portrait choice.

— Zoom lenses. There are only three true “zoom” lenses for digital rangefinders: the 16-18-21mm Tri-Elmar, the 21-35mm M-Hexanon Dual, and the 28-35-50 Tri-Elmar. The first two are expensive ($>2000), and the third is kind of ho-hum. And none of them is a true zoom; they are all lenses that have two or three discrete focal lengths. This is an area where the things that are most fun are not intuitive. Wide-angle zooms can be unwieldy when adapted to digital cameras; telephoto zooms can be somewhat challenging to control (but have some merits). The midrange zoom is where your sleepers lie, and if you are a heavy EVF user, a good, compact 35-105mm is not a bad thing to have around. One to check out is the AF 35-105 f/3.5-4.5D Nikkor ($100-150 used). This is a tiny, aspherical, internal-focusing push-pull zoom. It is quite sharp and contrasty, and if you ever get back to your Nikon DSLRs, it is quite a nice lens. It was not a cheap lens when it came out, but selling at around $100 today, it’s one to consider.

— Novelties. Many fun (and very occasional functional) accessories were made for SLRs – cheap fisheye lenses, 90 degree attachments, telescope adapters, and the like. For occasional use, these can be economical and entertaining. Fisheyes in particular are something that are, for most people, not worth investing in. Many of these lenses want 24×36 sensors to reach their full, ahem, potential.

Conclusion. It’s probably not good to counter one generalization (that old SLR lenses are no good) with another (that they are all good). For people who occasionally need a focal length, frequently use EVFs to focus heavy fast lens or telephoto users, or are already zone-focusing wide lenses, older SLR lenses are an avenue that might be helpful. Not every SLR lens is a great performer at a small pixel pitch, but there is value in seeing what can be done more simply and cheaply than forking over another several hundred (or several thousand) to buy a native RF or mirrorless lens that comes out of the bag once or twice a year.