My C/Y 50mm f/1.7, when adapted to Canon, mirror-hangs on my 5Dc. been told I need to grind down a 'fin'. Is that the tall aperture-controlling moving fin, or the protruding stationary fin right next to it?

umihoshijima wrote:
My C/Y 50mm f/1.7, when adapted to Canon, mirror-hangs on my 5Dc. been told I need to grind down a 'fin'. Is that the tall aperture-controlling moving fin, or the protruding stationary fin right next to it?

Whatever protrudes the most. For the aperture lever you could also use wire cutters (cut off 1~2 mm) in order to minimize the stress on the aperture mechanism.

If the mirror already hung on the lens, look for faint wear / rub marks. IIRC I had to remove a hair of material not from any of the protruding bits, but actually the flat surface. I had a photo somewhere here that I can't find anymore (maybe in archives 2011) of where I shaved the lens.

The fin will be at the 12:00 position when looking at the back of the lens with the DOF scale also at the 12:00 position.
You probably don't have to remove much, file it at an angle so the length doesn't change, so it might me still used on a C/Y body.
You should be able to see how much needs to come off by turning the focus after the mirror is hung from infinity to the point it doesn't hang, it's best to file some, test it, file some more, test it, & repeat.

I don't have a before picture but this is what it looked like after I shaved it.

LightShow wrote:
You should be able to see how much needs to come off by turning the focus after the mirror is hung from infinity to the point it doesn't hang, it's best to file some, test it, file some more, test it, & repeat.

Changing the focus doesn't change the position of the aperture lever & fin (if those are blocking the mirror) .

Before going the "grind" route, did you try to go with any different adapters for your 5Dc?

I just did, and out of 5 adapters, 2 work, and 3 are being sent back. The two that worked for me: the Fotodiox and EXPhoto ones from Amazon. They were in $20-$30 range...

LightShow wrote:
You should be able to see how much needs to come off by turning the focus after the mirror is hung from infinity to the point it doesn't hang, it's best to file some, test it, file some more, test it, & repeat.

AhamB wrote:
Changing the focus doesn't change the position of the aperture lever & fin (if those are blocking the mirror) .

The fins on the "back element" can hit the mirror and these move as you focus. At infinity they will hit the mirror regardless of which adapter you have.

Mark Rodz wrote:
Before going the "grind" route, did you try to go with any different adapters for your 5Dc?

I just did, and out of 5 adapters, 2 work, and 3 are being sent back. The two that worked for me: the Fotodiox and EXPhoto ones from Amazon. They were in $20-$30 range...

Are you actually able to focus at infinity without taking off the fins?

surf monkey wrote:
The fins on the "back element" can hit the mirror and these move as you focus. At infinity they will hit the mirror regardless of which adapter you have.


What fins? The guard fin for the aperture lever is part of the tube/barrel that you shaved, right? I know that with some lenses the rear element retaining ring gets in the way of the mirror but I've never seen a rear element with "fins".

Yup my mistake, was transposing my Rokkor 58/1.2 with my Contax 50/1.7, I was thinking the troubled part moves like my Rok.
Thanks for correcting my error.

Guess that lens won't be going onto a contax body anytime soon

I'm sure many would be happy to see a FF Zeiss Ikon/Contax EVIL, I know I would.

brucemuir wrote:
Guess that lens won't be going onto a contax body anytime soon


I believe that the aperture lever is the one on the right and is barely shorter than it originally was. The short lever on the left is untouched. I'm not sure what purpose the short lever serves (maybe aperture readout?).

Yes it is. When aperture is changed that lever moves. On a Contax body the DOF-preview button pushes that - and if it's just grinded to fit a Canon body it should still work on a Contax.

I have not had the 50/1.7, but what's common for many other Contax lenses is a small "fin" next to the aperture lever. Looking at the top ring it looks like something could have been grinded down there, just above the screw on the middle ring. That's where the fin usually is. Normally it is just a rectangular bit sticking out, but on e.g. the CY 100/2 it's quite a large triangular shaped thing there (that's at least what's on my MMJ version).

I was talking about the short lever on the left side, near the red dot. That one moves with the aperture ring but can't be pushed -- the aperture lever on the right can though.

Sure, I was just trying to elaborate that there are other protruding things too. Including trying to pinpoint something probably missing (grinded off) in surf-monkeys image.