Manual focus adapted lenses on an EOS 3

MAubrey · Dec 11, 2016

So, I was hoping that I'd be able to use my new-to-me EOS 3 for film the same way I used my old 5D: with adapted MF lenses from a variety of manufacturers, but it seems that there's a lens detection switch somewhere that causes a BC error if the lens doesn't have electronic contacts.

Does anyone know if there's a way around this other than merely not letting the lens click and lock into place?

emacs · Dec 11, 2016

I found this thread on photo.net which seems to be the same issue you have:

"On some EOS bodies there is a small microswitch in the lensmount which must not be tripped by any attached lens or lens adapter in order for the camera body to work. If an adapted manual focus lens trips this microswitch, the camera body them looks for a valid EF series lens to be attached. If it doesn't see the correct electrical connection the the camera body thinks there is an error condition and will not operate. I've never been able to find an official list of which bodies have this switch and which don't. The early 1D series bodies do, up to the 1D MkII. The 1D MkIII doesn't. I think the D30, D60 and 10D have it too (note that's the D30/D60 not the later 30D/60D). Some, possibly all, EOS film bodies have it. I know the EOS-3 does for example."

The OP ended up snipping that switch off, not sure if you want to get that destructive but I couldn't find any other solutions. Perhaps adapters with a focus confirmation chip would work?

Cholentpot · Dec 11, 2016

I've used a manual adapted lens with my A2 with great results. Don't leave the lens on though for extended times. It'll drain your battery when the camera is off.

David A. Goldfarb · Dec 12, 2016

I haven't run into that issue on my 1N-RS or 5DII, and most of my lenses are adapted manual focus lenses.

MAubrey · Dec 12, 2016

emacs said:
I found this thread on photo.net which seems to be the same issue you have
...
The OP ended up snipping that switch off, not sure if you want to get that destructive but I couldn't find any other solutions. Perhaps adapters with a focus confirmation chip would work?

Thanks. I might do that. My EOS 3 is a bit of a beater any way, so I don't think I'll loose much by going the destructive route. Otherwise, I'd need a whole lot of confirmation chips.

Ko.Fe. · Dec 12, 2016

Does with error comes from adapters with electrical contacts? I used it on 5D and it was even confirming focus.
http://www.ebay.com/itm/AF-Confirm-...484654?hash=item33838e79ae:g:EgIAAOxyLiJR185m
With AF-Confirm Clip.
EXIF is fixed 50mm f1.4.

emacs · Dec 12, 2016

I've coincidentally just picked up an EOS 3 today, and while I don't have an adapter to test out, I was able to get the camera to fire without a lens by switching CFn 5 to either 2 or 3. Might be worth trying before permanently modifying the camera.

Ron789 · Dec 12, 2016

I experienced the same using old Carl Zeiss lenses with adaptors on the EOS 1n and EOS 3. The bayonet is indeed tripping a switch. Filing off one of the tabs of the adaptor bayonet will fix it. The switch is on the left side of the bayonet mount, looking at the camera from the front.
To check whether this is indeed the problem unlock the lens and loosen it a little. In my case the BC error disappeared after turning the lens some 2 mm, so you need to file 2mm off the bayonet tab of the adaptor.
In addition: cover the bottom part of the adaptor with tape: without tape the adapter will cause the electrical contacts at the bottom of the lens mount to get connected and produce weird results.
I have modified several adaptors this way and they work fine now.

Ron789 · Dec 12, 2016

Here's a photo of a modified adaptor: the bayonet tab is at the 2 'o clock position; some 2mm was filed off. It looks a bit messy but it works fine.

MAubrey · Dec 14, 2016

Lots of good information, everyone. I'm going to take a look at the custom functions options, but it's good to know that if that doesn't work, I can just modify my adapter rather than permanently damage the camera.

I'll report back soon...

MAubrey · Dec 14, 2016

Ron789 said:
To check whether this is indeed the problem unlock the lens and loosen it a little. In my case the BC error disappeared after turning the lens some 2 mm, so you need to file 2mm off the bayonet tab of the adaptor.

Yep, that's exactly the problem. I can fire any lens with an adapter if I turn the lens slightly before it clicks in the bayonet.

Joshua Reisbord · Jan 17, 2024

Figured I would drop by with a solution 8 years later! The switch is located to the left of the mirror right below the EF ring on an EOS 3. When the switch is tripped by the flange on the adapter or EF lens, the camera then checks the electrical connection between the contacts to the bottom of the mirror. This is why when you adapt a manual lens to an EF camera (specifically speaking about the EOS-3) you get a BC error. As mentioned by @Ron789 above you can modify the adapter ring so it does NOT trip this switch. I have attached photos of the modification I made and the switch location on the camera.

As a side note, some people have mentioned in other threads that a chip needs to be on the adapter for a manual focus lens to work, however, I find this still has the chance of throwing a BC error. If you are using a manual lens, why use a chip of unknown quality?

(http://imgur.com/a/SsuN6lK)

Les Sarile · Jan 17, 2024

I used an Olympus OM to Canon EOS adapter and can use OM lenses on my EOS1. THE OM Varimagnifier also mounts and works great too . . .

EOS1 OM by Les DMess, on Flickr

MattKing · Jan 17, 2024

Les Sarile said:
I used an Olympus OM to Canon EOS adapter and can use OM lenses on my EOS1.

The same applies to my four Rebel 2000, 7N, 7E, and IIe.

Ramajai · Jul 21, 2025

Joshua Reisbord said:
Figured I would drop by with a solution 8 years later! The switch is located to the left of the mirror right below the EF ring on an EOS 3. When the switch is tripped by the flange on the adapter or EF lens, the camera then checks the electrical connection between the contacts to the bottom of the mirror. This is why when you adapt a manual lens to an EF camera (specifically speaking about the EOS-3) you get a BC error. As mentioned by @Ron789 above you can modify the adapter ring so it does NOT trip this switch. I have attached photos of the modification I made and the switch location on the camera.

As a side note, some people have mentioned in other threads that a chip needs to be on the adapter for a manual focus lens to work, however, I find this still has the chance of throwing a BC error. If you are using a manual lens, why use a chip of unknown quality?

(http://imgur.com/a/SsuN6lK)

Hey I am having similar issues. Just grabbed a pretty decent deal on a Carl Zeiss Distagon 2.8/28mm with a FotodioX Pro CTX-EF adapter. Wondering if you could help me modify it , a little confused which part of the adapter to file down so it doesn’t trip the switch. Works pretty much up until I trip that switch hahaha.

Manual focus adapted lenses on an EOS 3

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Manual focus adapted lenses on an EOS 3

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