5D mods to work with Contax 28mm 2.8

Registered: Sep 21, 2005
Total Posts: 11
Country: United States


I am using a Canon 5D and a Contax 28mm 2.8 with both the Cameraquest and Son Mihn adapters. I have two 5Ds . One works with both adapters and the other the mirror hits the back of the lens with both adapters. I still can't figure out this discrepency.

from what I have read on the forum, it seems the two options are to trim the camera mirror or shave a piece off the back of the lens. Is this correct?

My mirror is only getting caught on the way down. How can this be? How does it clear the lens on the way up but not on the way down?

Finally, If I have to modify the lens, what is the least severe mod needed to get it to work?

If, instead, I choose to modify the mirror, what is the least severe mod I need to make to get it to work?

Andi Dietrich
Registered: Nov 13, 2005
Total Posts: 0
Country: Bahamas

I had no problem with this lens using a FS adapter, sanded down just a bit. Even my 18 was ok with this adapter.
Difficult to believe but interesting to many. We heard so much about differences in 5D mirrors, can you publish a photo of that lens?

Registered: Nov 08, 2005
Total Posts: 643
Country: Canada

Mirror up is by motor and mirror down is by spring. The mirror may have hit the lens on the way up but the motor is powerful enough to make it through. To see if this is the case, you may listen carefully to see if the noise is different between a Contax lens and a Canon lens in bulb mode.

Registered: Oct 11, 2005
Total Posts: 3059
Country: Sweden


I would not trim the 5D mirror for a CZ 28mm lens, this is how I and some others have done it; there seems to be a variety in tolerance on 5D cameras as to the mirror box so your mileage may vary but doing this little mod on the lens will fix it.

Remove the three screws around the back lens element, then remove the black plastic collar that surrounds the rear lens element.

As you can see the collar is a bit uneven in shape, it being higher near wher the fin is located. File it down a bit so it is even and not sitting higher than the adaptor rim. Also the fin on the lens needs to be filed down to the same height, but normally a mm or so will suffice.

By removing the collar before filing it down you reduce the risk of getting plastic debris in to your lens, the fin you can just mask of by putting a small clear bag over the lens, poke a hole for the fin and tape around it to seal it off, then use a Dremel or a small file.

Easy peasy.

Registered: Oct 11, 2005
Total Posts: 3059
Country: Sweden

You could try shaping the collar first and leave the fin.

When I got my 28mm it cleared from the start on horisontal shots but hung the mirror on verticals (!) so I started with filing down the fin, all the way down to the plastic collar.

Done. I thought. But the mirror still hung up on verticals (!) so I examined the lens when seated in the adapter and saw that the collar did protrude over the rim of the adapter.
So I took it out and filed it down and refitted it, and that did the trick.


Shaving the mirror is something I'd only do if I had a few killer expensive lenses I needed to fit. By shaving the mirror you void warranty and will have a tough time selling it if you wanted to, unless to one of us crazee guys on this here forum...

Registered: Jan 25, 2005
Total Posts: 897
Country: Germany

Henrik, the shaving of the fin and the aperture lever would mean that the lens would not be working on a Contax SLR ?!? I guess they are there on purpose... But since we are talking about a camera out of production I guess that's not that important. I was thinking about doing the same to my lenses in order to be able to mount the af confirmation chip, but was a little worried since it would mean that the lens would be a EOS-only lens in case I would sell them again...
Regards, Stefan

Registered: Jan 03, 2005
Total Posts: 7174
Country: United States


The old conventional wisdom (when the 1Ds/1DsMKII was the only body used), was to modify lenses, as only a handful reguired modicfication. This got to be pretty hairy, as some of these were multi-thousand lenses that were having their re-sale value permantly affected.

You are the perfect example of the 5D conundrum that no one believed- the 5d mirror is all over the place for reasons that no one knows. With the camera being the device that becomes obsolete faster, it now makes more sense to modify that, and leave the lenses alone. Great German glass holds its value well, and I intend my arsenal to be my last lens collection that carries me through to retirement. (providing I continue to use EOS mount cameras).

If all you want to do is use one $300 CZ28/2.8, well, then use it on the body that clears. If you plan to acquire a collection of the best of the best, then modify your cameras.

Registered: Oct 11, 2005
Total Posts: 3059
Country: Sweden

I agree with John: when the worth of the lenses you plan to hold on to exceed that of the camera, which is likely to be slightly dated anyway in a few years, then go ahead and chip that mirror. I would.

But in this case, with the 5D I think it is more sensible to mod the Zeiss 28mm.

Yes, it won't work very well then on the old Contax film based SLR's but hey - are you going to use film anyway in the next few years?

The 5D is much much more expensive than that Zeiss 28 and how do you explain to the next buyer that you HAD to do it .

Also, the mod on the Zeiss 28 still ensures you can use it with your next digital SLR as well.
Also if you sell it for a dSLR user he probably won't mind the mod.

To me it is obvious. But I can be a bit thick.