M42 lens compatibility for digital SLRs and others

from Shutter, by Lewis Collard

Work, as my hero Jason Scott says, tends to be fractal. While I was working on my Pentacon 50mm f/1.8 review, I realised that I could easily break out the section on using the lens with modern cameras into a whole separate page on using M42 lenses on modern cameras. I found that, too, was fractal, so if you ever find that I've made a chart on interoperability between every single thing on every camera system ever...well, you know how that came about.

But I resisted the temptation! So here it is, the big chart of using M42 lenses on modern camera systems. All of these systems will require that an adapter is used; what's being discussed here is how useful your camera will be after you've gotten one. Links in the first row and first column take you to the relevant subsections of this page.

What this all means

Optics required

This means that any adapter will require corrective optics to be able to focus to infinity.

The flange-to-film-plane distance of the M42 lens mount is 45.5 millimeters. If it's longer than that for your camera system, then you're going to have a bad time, because that means you've effectively got a small extension tube, and you can't focus to infinity with an extension tube. On top of this, you might have to add on a millimeter or two for your adapter.

You can get adapters with corrective optics, but I don't like the idea for three reasons:

• The quality of these adapters is far too variable. I don't know if any of these are made by serious optical companies. Thus, you're likely to get serious degradation of the image.
• They act as teleconverters, which exacerbates the crop-factor problem.
• The above also means that your effective aperture is smaller.

If you want to find out the furthest distance to which you will be able to focus using an adapter without corrective optics, then try this:

1. Go to this lens magnification and depth of field calculator.
2. Enter the focal length of your lens in the appropriate place.
3. Set "focusing distance" to a very large value. Try 50000. (50 kilometers may as well be infinity.)
4. Subtract 45.5 from the flange focal distance of your lens mount (in millimeters), then add an arbitrary thickness for your adapter if necessary. So for Nikon F, that's 46.5 - 45.5 + (1 or 2) = 2 or 3 mm. Enter the resulting number into the box marked "extension tube".
5. Hit "calculate" and the box marked "effective focusing distance" will tell you roughly where your infinity focus will be. Huzzah!

Try it with various focal lengths; you'll notice that telephotos are much more useful than wide and normal lenses.

Focus confirm

This is important for autofocus SLRs, which do not have optical focusing aids like a split-image or microprism ring, to get accurate focus quickly. This is especially so on small-sensored SLRs with tiny viewfinders, on which manual-focusing is much harder. This becomes irrelevant if your camera has live view with zoom.

Metering

Some cameras are dependent upon the presence of a chip on the lens to know that there is a lens attached; as far as the camera is concerned, an M42 lens fitted via an unchipped adapter is the same as having no lens at all. Some of these cameras will refuse to meter if they don't know they have a lens attached. If this is the case, you will be stuck in manual mode, and you will have to measure the exposure by other means (or guess it).

High-quality adapters

I use this as shorthand to refer to adapters that were made by the manufacturers of the camera bodies. In this case, Pentax made them for their K-mount, and Canon made them for their FD cameras. Canon and Pentax are serious companies who know how to make this sort of thing precisely and consistently. An adapter made in a one-man machine shop in China won't necessarily be produced this accurately.

These adapters are not necessarily available new anymore. I'm sure the Canon FD one isn't, anyway (!).

If your only option is to get one of the cheap, non-camera-manufacturer adapters and you absolutely must have dead-on infinity focus across the whole frame (such as for astrophotography), then you're going to need either some mechanical engineering skills or extraordinary luck.

There might be aftermarket ones out there which are made to the quality of Pentax's and Canon's adapters; these guys look promising, and expensive.

Crop factor

This is the size of the sensor relative to the size of the 35mm film for which M42 lenses were designed. A crop factor of 1x means that the sensor is the same size (full-frame cameras), 1.5x means that the sensor is 50% smaller if you measure the diagonal.

This has three effects, one obvious that you all know about, two less obvious:

1. The effective focal length of the lens is increased. For example, a 58mm lens on a camera with a 1.5x crop factor behaves just like an 87mm lens on a film camera. This can either be good or bad depending on your perspective; it's up to you whether your 29mm f/2.8 wide-angle lens becoming a 43.5mm f/2.8 normal lens is good or bad. But do remember that M42 lenses will be designed with focal lengths intended to be useful for a film camera.
2. You may find that an M42 lens will be less sharp than a lens designed for your sensor. Remember, if your sensor is half the size of 35mm film, then any lens has to resolve twice as well within that area to be as sharp at any given enlargement. Lenses that are designed from scratch to do that have no problems doing so. Lenses designed before your digital camera was even imaginable may not do this very well. This is somewhat mitigated by the fact that all M42 lenses are at least a little sharper in the centre than they are at the edges.
   
   You won't know this for sure without either getting (and understanding) an MTF chart for your lens, or trying it on your camera. Just don't be upset at the lens for not doing something it was never intended to do.
3. Connected with the above: We're used to having lenses in sensible focal length ranges that are just about perfect. For example, even Nikon's plastic 18-55mm kit lens is a very sharp lens for cameras with a cropped sensor. A 20mm lens in the 1960s and 1970s, for a full-frame camera, was a serious technical challenge; photographers were happy to sacrifice a little technical quality (or stop down to f/8) if it meant they could have a lens this wide. Thus, once again, don't expect M42 lenses to be as sharp as a lens with the same focal length designed for your sensor.

An unimpressed cat, shot with a Helios 44M-4 58mm f/2.

System notes

For all camera systems

If you have the option for it, shoot your camera in centre-weighted metering mode. Matrix (evaluative) meters will get very confused by the dark image coming from a stopped-down lens.

If the camera needs a chip for certain functions to work, it might be a bad idea. Cameras have been toasted this way and it will certainly void your warranty.

Fuji made a series of "M42" lenses designed for their "M42" cameras like the Fujica ST705, with an additional mechanical lug to give you open-aperture metering on those bodies. These will not mount on an M42 adapter, so don't try it. (The silliness goes both ways; using normal M42 lenses on these cameras requires that you hit both the depth-of-field preview button and half-press the shutter for metering.)

Canon EF/EOS

Beware of the 5D, and probably other full-frame cameras. The rear element of some M42 lenses will collide with your mirror when focused to infinity. See over here for more information.

Otherwise, you're OK here, except you'll need an adapter with a chip to get focus confirmation. Don't bother with these if you have live view; use that instead for better results. You used to be able to get focus screens with manual-focus aids, but Haoda doesn't seem to be around anymore and KatzEye Optics are no longer taking orders. Oh well.

Shoot this in Av (aperture priority) or M (manual) mode; the other modes won't work properly.

Canon FD

The Canon FD mount went obsolete in 1987, but I threw it in with the modern lens mounts for fun. I love the A-1 that much!

As a general rule, if your camera can do stopped-down metering with Canon FL lenses, it'll probably be able to do stopped-down metering with M42 lenses via an adapter. I know that the T50 definitely won't work (unless the only shutter speed you ever use is 1/60). I know that the A-1 and T90 will work, and the F-1, T70 and AE-1 probably will as well.

Canon made an adapter for these, and adapters claiming to be genuine Canon ones are quite abundant.

Micro Four-Thirds

You should be fine here. You probably won't get focus confirmation, but you don't need it with live view. Don't get caught out by the crop factor, though.

You may have to enable a setting in the menus to tell your camera to shoot whether or not it thinks it has a lens attached.

Nikon F

See "Optics required" above; the flange-to-focal-plane distance for Nikon is a millimeter greater than that of the M42 mount.

Other than that, you should get focus confirmation on all AF bodies, but you won't get metering on many of them. As a general rule, I gather that if your camera can meter with manual-focus lenses, it'll give you metering with an M42 lens mounted via an adapter. The single-digit and three-digit cameras (except the old D100) should all be fine, and so should the D7000.

I'm not sure it's worth bothering with on Nikon. On the other hand, see what this guy did with a D700, Pentacon 135mm f/2.8 and non-correcting adapter. It looks fantastic!

Pentax K-mount

Pentax are real compatibility superheroes, as always. They care so much about lens compatibility that they've ensured you can use your Pentax digital SLRs with old Pentax lenses that went obsolete in 1975. Did you know that Pentax even sells an adapter so you can use lenses from their medium format cameras on your digital and 35mm SLRs? No sane person has ever used one, which means that Pentax even loves insane people, too. Thanks, Pentax! For contrast, some Nikon F-mount digital SLRs won't meter with manual-focus Nikon F-mount lenses that Nikon makes today.

Pentax made an M42-to-K-mount adapter until not so long ago. I don't think it's still being manufactured, but you definitely want to find one of these rather than the knock-offs; even if I didn't know that the genuine Pentax adapters are mechanically superior, I'd recommend you buy one just to thank Pentax for caring so much about you.

We love you too, Pentax! ♥ ♥ ♥

Sigma SA mount

I've marked this as "not recommended" because there are reports of aperture stop-down pins on "auto" M42 lenses interfering with the mechanics of the camera. This is OK if you only intend to use lenses without aperture stop-down pins, but it could get very messy otherwise.

A solution to this is to use an adapter with a flange to push the stop-down pin so that it doesn't interfere with the mechanics. The problem with this, as far as I can tell, is that the location of the stop-down pin is not standardised in the M42 system. Thus, to ensure it works with all M42 lenses, you need quite a wide flange. But, that also means that some lenses with large rear elements will collide with this thick flange, and thus you will not be able to focus to infinity.

"Not recommended", despite the bold red capital letters and skull-and-crossbones symbols (Unicode is fantastic, isn't it?), is not the same thing as "certain death awaits thee". It means I think it's probable and I don't want anyone to be angry at me for saying something was OK when it was not. I don't own a Sigma camera, so anyone should feel free to correct me if they have tried it.

Sony Alpha (previously Minolta AF)

There's a whole FAQ about this over here. You will need an adapter with a chip to get SteadyShot in-camera image stabilisation, otherwise, as long as your body has an option to shoot without a lens attached you should be able to shoot in aperture-priority mode, if you have the latest firmware. Otherwise, M is supposed to work. I haven't tried any of this, but those guys have.

Sony E-mount

The tiny flange-to-focal-plane distance of the E-mount lenses works in your favour here. There's so much free space to play with that you can even get a tilting adapter!

You may need to go through your menus to change a setting that allows the camera to fire without a lens fitted. (Remember, the camera doesn't know it has a lens attached via an adapter.)

I don't know how focus confirmation works on these cameras, or if you have zoom on live view. I suspect on the latter count that you do.

The Helios 44-2 looks pretty funny on a Sony NEX.

A very serious cat, shot with a Helios 44M-4 58mm f/2.

On "auto" and "manual" lenses

Early M42 cameras had no ability to stop down the lens while shooting. You would open the aperture to focus, then manually stop down the lens to meter (if you had a TTL meter!) and shoot. These lenses are called "preset" lenses.

Later, manufacturers added mechanisms to cameras and lenses that would allow the camera to do the work of stopping down the lens. You'd still need to meter while stopped down (cameras had a button or lever on board to activate the meter and stop down the lens), but you could focus wide-open and the lens would be stopped down when you fired the shutter. These lenses are called "auto" lenses; that's about as much automation as you'll get in the M42 system.

For backwards compatibility with older cameras that did not support this "auto" feature, most lenses had an "M/A" switch that would allow you to operate them as preset lenses. The trick here is that your digital camera with the adapter is exactly like one of these ancient cameras because it doesn't have a mechanism to stop down the lens either.

(Side note: The Pentacon 29mm f/2.8 did not have an M/A switch; instead, it had a spring-loaded button on the side of the lens which would stop down the lens when pushed in. If you're shooting this on a camera which does not have a stop-down mechanism, then you either have to shoot it wide-open or hold down the button while shooting. This is a pain, and it also means you're prone to camera shake, making it nearly useless for tripod-duration exposures. A shame, because that lens really needs to be shot at f/8 or f/11 to be really sharp.)

So, if you're looking for lenses to use on your digital SLR, I'd recommend you do one of the following:

• Get a preset lens, or a lens with an A/M switch. As said, this is most, but not all, M42 lenses. Just look for either the lack of a stop-down pin on the rear, or the presence of an A/M switch.
• Modify your lens. This is usually not a very difficult operation; I've done this before. But do bear in mind that this will destroy any collectible value your lens has, now or in the future. You won't worry about this with lenses like the Helios 44-series; these were made in untold numbers and will likely always be ludicrously cheap.
• Get an M42 adapter with a flange to push the pin down. I personally would not do this (which is why I don't recommend using M42 lenses on Sigma cameras). Some adapters have a very wide flange that will interfere with the mechanics of your lens and prevent you focusing to infinity. Others have a narrower flange that might not be wide enough to reach the stop-down pin on all lenses. Also remember that the internal mechanics of these auto-only lenses were never designed to have the stop-down pins held flush with the body of the lens full-time; I won't discount the idea that you could damage the lens' mechanics if you do this for long enough.

Andre, shot with a Pentacon 135mm f/2.8.

Summary

It's up to you whether it's worth doing this. For Nikon, I'd say it's not; they barely work on many camera bodies, and you won't get infinity focus on any of them. Besides, three of their cheapest plastic lenses (18-55mm, 50mm f/1.8D, 55-200mm VR) are optically so good that you don't need these weird ancient manual-focus lenses. But once again, always listen to the one doing it and getting astounding results, not to the guy with the opinions who is not.

On the other hand, there's a lot to love about M42 equipment:

1. Digital SLR film-makers who like primes will love lenses like the Pentacon 135mm f/2.8; there is nothing made today at any price that gives you manual-focus so precise, and very few lenses have such amazing bokeh. And I suspect they'll love the old preset M42 lenses with stepless aperture rings.
2. Most M42 primes are made of solid metal, so those of you that like holding a good, solid chunk of engineering will be happy.
3. M42 lenses are cheap, and so those of us who like playing with stuff have no reason to not own a few of them.
4. Some of them are cheap and astoundingly good, like the aforementioned Pentacon (£30 for a 135mm f/2.8!) and a couple of other cheap mid-tele surprises that I've read about.
5. Even the less stellar lenses can be used for fantastic results if you know how to use them.

Let me know how you get on with them!

Help me

I can't own, test, or research every possible camera system, so your camera system might be missing. I'd like to know how M42 lenses work on other camera systems that I have not listed, and especially, I'd like to know how they work on professional video camera setups. If you've tried this, let me know.

Thanks to Jenn, Jenna, Trissy and Angelique for proof-reading this for me.