How to shim Argus C3 lens mount?

[RLangham]

Sorry for two threads about my dumb ancient camera in one day, but now that I'm on the subject...

So on my good Argus, lenses screw in too far. I didn't notice until my Soligor 135mm came in the mail, since the Cintar 50mm doesn't really have anything to show you that it's out of position. Then I assumed it was a problem with the Soligor. Today I bought a Sandmar 35mm and completed the trifecta and sure enough, it screws in too far too. And it's definitely making infinity soft. It's less noticeable on the 50mm, and I'm sure even less noticeable on the 35mm, but it's enough to bother me.

Now, it hasn't damaged the shutter, but I can't understand how to fix this problem. Surely I can't put a washer-shaped cardstock shim in the lens mount--it would press on the protrusions from the individual shutter leaves and bend them. This is my favorite camera so I'd like to fix it...

 

[DWThomas]

Maybe engagement of the idler wheel is off a tooth? The 50mm Cintar has about 6 parallel threads in its focus helicoid and only one is right. I don't own the other lenses so I have no idea of their idiosyncrasies. I'm thinking the lens focus movement may go "beyond infinity" but the travel is limited by the idler gear at each end of the range. Any of the lenses known to be right on other cameras?

 

[RLangham]

Maybe engagement of the idler wheel is off a tooth? The 50mm Cintar has about 6 parallel threads in its focus helicoid and only one is right. I don't own the other lenses so I have no idea of their idiosyncrasies. I'm thinking the lens focus movement may go "beyond infinity" but the travel is limited by the idler gear at each end of the range. Any of the lenses known to be right on other cameras?

I routinely mount and dismount lenses. If the idler were off it wouldn't stay that way.

 

[ic-racer]

Coincidentally I have two C2 or C3 bricks in front of me. I serviced the shutter on one of them last night and will do the other today. I have not adjusted the focus on either yet, but I have the lenses off and can't really tell what you are referring to in screwing it to far. On both of mine the lens seats and the helicoid starts working right as the first teeth point right at the center of the idler. Can you show a picture?

Now if your "infinity" is when the last gear tooth engages and it binds and your images are "soft' at the image plane, then your focus adjust ring (held with the 4 small screws) might still not be adjusted correctly. So maybe try re-setting the focus calibration at infinity.

 

[Hunter_Compton]

I can't speak to the accessory lenses, but on the 50mm Cintar, there are three set screws around the front barrel that when loosened allow you to adjust the position of the helical, and thus the infinity focus. I would assume that the other lenses also have some mechanism to adjust the infinity focus, as the screw mount is not supposed to be used to change the infinity focus.

 

[RLangham]

I can't speak to the accessory lenses, but on the 50mm Cintar, there are three set screws around the front barrel that when loosened allow you to adjust the position of the helical, and thus the infinity focus. I would assume that the other lenses also have some mechanism to adjust the infinity focus, as the screw mount is not supposed to be used to change the infinity focus.

Have you done this personally? What do I do after loosening the screws? Pull the barrel out until it looks sharp at the focal plane?

 

[RLangham]

Coincidentally I have two C2 or C3 bricks in front of me. I serviced the shutter on one of them last night and will do the other today. I have not adjusted the focus on either yet, but I have the lenses off and can't really tell what you are referring to in screwing it to far. On both of mine the lens seats and the helicoid starts working right as the first teeth point right at the center of the idler. Can you show a picture?

Now if your "infinity" is when the last gear tooth engages and it binds and your images are "soft' at the image plane, then your focus adjust ring (held with the 4 small screws) might still not be adjusted correctly. So maybe try re-setting the focus calibration at infinity.

I mean that when a lens seats, and is engaged with the gear at the first tooth, it is soft at the image plane and/or the third-party lenses have the distance/DoF scale down around the side instead of on top.

 

[ic-racer]

Yes sounds like focus calibration is off. I just checked both of mine with a microscope slide and semi-transparent tape and they are good. But if they were off, I'd loosen the 4 screws and twist the barrel until infinity is in focus, then tighten the screws. Infinity is the hardest thingamera on which to focus, so if you get that correct, the close distances will fall in place.

 

[Hunter_Compton]

Have you done this personally? What do I do after loosening the screws? Pull the barrel out until it looks sharp at the focal plane?

Yes, loosen the screws at the front of the lens barrel, you will now be able to turn the lens helical independently of the focusing mount. Set the RF to infinity, place ground glass or similar on the film plane, then turn the helical until everything is in focus and tighten the set screws.

 

[RLangham]

Yes, loosen the screws at the front of the lens barrel, you will now be able to turn the lens helical independently of the focusing mount. Set the RF to infinity, place ground glass or similar on the film plane, then turn the helical until everything is in focus and tighten the set screws.

Success! Boy was that easy. Thanks for telling me!