Excursion – Lens Adapters

In this article I would like to present some of my adapters, what they can and cannot do and what the flange distance is and why it’s so important.

So, what is the flange distance?

To put it simply: it’s the distance between lens and film/sensor surface. Usually every camera company choses their flange distance at will (within certain limitations) and therefore they differ a lot.

The flange distance in a rangefinder camera (or a digital mirrorless for that matter) is very short, as you can imagine, because there is no need to leave room for a mirror. In a classic Medium Format camera the distance will be massive because of the huge mirror that has to flap out of the way.

Now the question that remains: how does that matter for my purpose?

Firstly: the Canon EOS system has a rather short flange distance for a single lens reflex system. Wiki-Link

And that’s a good thing, because the flange distance is shorter than the largely established M42 or M39 screw mounts from back in the days, the Nikon F, Leica R, or Rollei QBM systems.

You see, in order to get any lens to work properly, the distance between lens and film/sensor plane has to be the same as it was originally intended to be.

If the flange distance for the Canon EOS system was larger than the one for M42, for example, I couldn’t adapt M42 lenses to my camera. (They would sit too far away from the sensor.) There are, of course, solutions for that case (e.g. with Canon FD to Canon EOS adaptors) but they require the inclusion of an optical element (to shift the focal plane of the lens) and the result would be an expensive adapter in order to achieve a high quality.

For that reason I focus on lenses that came from systems with a longer flange distance than my Canon requires. These lenses only require an adapter that fixes them to the camera and gaps the distance the lens needs to be away from the sensor plane. You can imagine that modern digital mirrorless systems are predestined for the use of vintage SLR glass, because they ALWAYS come with a shorter flange distance and therefore can take ANY lens given the right adapter.

Being of the purist kind I prefer to look through an optical viewfinder and the lens directly before I take my shot, so the whole digital thing would kill the vintage vibe for me.

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Will all lenses work on my Canon?

No, unfortunately not.

As a rule of thumb one can say that telephoto lenses will mostly work, because their rear element does NOT usually protrude inside the mirror box of the camera (this is not always the case!).

However, with many 50mm lenses (and wider) this problem can occur, especially with the Canon 5D/6D series.  The 1D (APS-H) and the APS-C Canons won’t have alot of problems, because they have smaller mirrors and therefore more clearance. Also, the 1Ds series obviously has a tiny bit more space in the mirrorbox, because I only have that problem with the Color-Ultron and none of my other fifties.

When I set the focus at infinity, the rear element will protrude quite a bit and the mirror will get stuck on top of it when it comes down after the exposure. The result is a camera error and a terrible sound coming from inside. (I only tested it once for every lens and won’t do it again with the Ultron. No video, I’m afraid!)

This image shows the rear element of the Color-Ultron when focused to its MFD and when focused at infinity. Don’t mind the dirt and dust everywhere on the lens.

this one shows better how little of a protrusion can cause the mirror to get stuck:

The Pancolar is also quite infamous for its protruding rear element and many people with Canon 5D/6D report it not working at infinity:

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If you adapt a lens that has a protruding rear element you would need to make sure that it won’t collide with the mirror. (Either by moving the lens further away from the Camera, therefore losing some of the focus range, or by not using the mirror at all, meaning shooting in live-view mode)

Here’s a List where people gathered their experiences about various lenses (M42 mount) and whether they would or wouldn’t fit on a Canon 5D (classic). (The 5D mk II and the 6D seem to be very similar, therefore these findings should apply as well.)

People there also offered solutions to work around these issues, sometimes by filing away parts of the lens…

Dustin Abbott recommends to use a tiny bit of double sided tape to gain extra space between lens and mirror for the S-M-C Takumar with his Canon 6D.

The Takumar does not hit the mirror with the 1Ds mk III, however.

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Now on to those adapters:

EMF AF confirm chips

You will notice that all my adapters have electrical contacts similar to those you know from your digital camera (and some more modern film cameras).

With modern DSLRs these contacts provide the camera with information about the lens attached (focal length, aperture, etc.) and enable the camera to tell the lens what to do (like selecting and setting the desired aperture, AF control, etc.).

Because vintage lenses lack AF and the aperture has to be set manually via an aperture ring, why should I even bother with these electronic contacts?

Firstly, you can program these chips and enter the maximum aperture and focal length for the lens it’s mounted on. This will be saved in the EXIF data (along with a really curious range of focal lengths (as if it were a zoom lens)) and when you set the aperture on the camera (Av or M modes), that will be shown too, so you can later tell what apertures you were using when shooting that lens.

Secondly, and to me the most important thing, the AF system only works if the camera thinks that there’s a lens in front of it.

Why would you want to use the AF system on a manual focus lens?

The 1Ds mk III (and many more Canon DSLRs) has  a focus indicator in the viewfinder that will glow (the selected AF point plus the green dot in the info line) and even a focus confirmation beep (sometimes I find it annoying, but I couldn’t be without it!).

This is how it works for me: I select the focus point that I want to focus on like I do with AF lenses and while half-pressing the shutter button I focus on that point (usually the eye closer to the camera for portraits) and as soon as it’s in focus, the AF point will glow brighter, the green dot appears and the beep sounds. At this point I take my shot and if it weren’t for my unsteady hands and the razor-thin focal depth at f/1.4 I would probably get mostly spot on sharp images. 🙂

Also there’s the issue of focus adjustment that I will have to look into next week. (I suspect myself being the cause but if I can rule out the camera I might be able to sleep better. Or not.)

I do have the Ef-S (high precision matte screen) installed and it makes focusing a lot easier, but my eyesight usually cannot compete with the AF system from the camera.

I even bought an EMF AF confirm chip (2 bucks, free shipping) to glue on my Samyang 35mm f/1.4 lens but didn’t get around to do that yet.

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M42 screw mount lenses

There are basically two kinds of lenses for M42 mount: the ones with an auto aperture pin and the ones without the pin.

What does the pin do? In SLR cameras that had the feature required it was possible to focus (and meter) through the open lens and the camera would stop the lens down to the selected aperture once you press the shutter. That was done by pressing down a pin on the lens barrel.

Before that time, or with cameras lacking that feature, the lens had to be stopped down for focusing and metering (so-called stop-down metering) which can get tricky at really small apertures.

If you happen to get a lens that has no such pin (such as the HELIOS for example) you could get an adapter like the following:

It’s a very simple but solid construction and costs less than 9 USD via eBay. (Shipping from China is free and there usually aren’t any customs fees for shipments at such low value.)

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If your lens has an auto-aperture pin you will need an adapter that keeps that pin pressed in all the time. The reason is very simple: the Canon cannot press that pin and without pressing it there’s only one way to take pictures: wide open! While that’s fine and fun for most times, it’s convenient to know that one can stop the lens down a stop or two for certain subjects.

In this image you can see the auto-aperture pin from my Pancolar 50mm f/1.8. You can also see that this pin sits inside the M42 thread and therefore won’t be touched by a simple adapter like the one shown above.

You will have to live with the fact that you have to look through the lens while it’s stopped down. When you set the aperture (in Av mode) according to the one set on the lens (helpful with the exif later) you will have to work around the cameras metering system. (It assumes that the lens is open all the time and setting a small aperture would result in overexposure. You have to meter with the lens wide open and the aperture set to the desired value, save the exposure (*-Button) and then stop the lens down to take the shot.

Adapters that keep the aperture pin pressed could look like this:

You might notice the little “flange” on the bottom of the thread. Again a picture of my Pancolar but with said adapter installed. the flange covers the area where the pin sits and keeps it pressed in.

Not all adapters are identical and the width of the flange varies between different manufacturers. In case of my Super-Multi-Coated Takumar I had to file off some of the flange because it was causing the aperture lever to get stuck between the rear element of the lens and the adapter (you see that lever in the top and the filed off part where the lever moves past shines silverish):

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Nikon F mount

When you have a Nikon lens you wish to adapt to your Canon camera make sure that the lens has an aperture ring. (The ones that come without aperture ring are made from plastic anyways and we don’t want these!)

The adapter usually is more complex than the ones for M42 systems, because the Nikon system is based on a locking mechanism with a pin that holds the lens in place (you see that pin on the right).

On the back it looks like this:

You see the pin-lever held by a spring that keeps the lens in place. Different adapters come with different mechanisms to move the pin (my adapter for the micro Nikkor is different, for example, but it sucks precision-wise with way too much play causing errors on the camera!).

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Rollei QBM mount

I bought the Voigtländer Color-Ultron in QBM mount even though it is available in M42 mount. The reason is pretty simple: people pay twice as much for an M42 version of the lens and there’s a simple way to get the QBM lens mounted on a Canon.

The QBM mount on this lens is held by three simple screws and there’s a QBM-Canon EOS conversion kit available on eBay for a mere 15 bucks. (that’s 5 bucks more than a chipped M42-EF adapter costs and you saved 100 bucks on the lens!)

The best thing for me is the fact that the lens now has a fixed Canon EF mount and cannot under any circumstance get lose or anything.

There’s just one thing that annoys me with the QBM-conversion kit:

1. The auto-aperture pin despite being pressed in all the time (that tiny metal plate held by two screws holds it in place) the aperture won’t close because it’s somehow stuck. The pin in this lens is part of a very complex construction (yes, it jumped out at me yesterday and it took me 2 hours to fix it again..) The aperture will instantly close when I slightly lift the adapter and also if I hold the pin down manually.

Edit: I fixed the problem today. The original adapter had a little protrusion around the area of the auto-aperture pin. This protrusion also spanned the place where the other, spring-loaded, part of the auto-aperture mechanism sat. A friend suggested that this part would have to move for the aperture to close and therefore I took a file to my QBM-adapter and filed away at that very location. After lots and lots of filing I created a little protrusion and tested it on the lens.

Now the aperture works perfectly fine, opens and closes when I want it to. 😀