Contax RX - Significant focusing issues

[Zaxx]

Hi all!

I recently got a hold of a Contax RX in great working condition, but for one thing - focusing through the viewfinder is not at all accurate using the split prism or ground glass. Attempting to focus at an object at infinity, the split prism indicates critical focus at approx. 3m on the lens' focusing scale. Likewise, an object at 3m distance the split prism shows as critically focused at 1.5m on the lens' focusing scale, etc. I believe I have eliminated the following causes (though I could be wrong):

i) The lens: The RX's Digital Focus Indicator works properly and allows for accurate focusing, verified against other cameras I know to be accurate. So it isn't a lens calibration problem.
ii) The focusing screen: The focusing screen is of correct type as far as I can tell (FW-1) and is properly seated in the correct orientation.

So I can only think that the cause is the mirror. I tried using a piece of card as a shim to raise the mirror's resting position and this compounded the problem, which leads me to believe I am right that the mirror is improperly positioned. There is no "mirror slip" that I can see. I have a couple of theories:

a) The mirror is not stopping back at a proper 45 degree angle and the mirror stop needs to be adjusted (I believe from reading the RX repair manuals that it is adjustable?)
b) A previous owner has repaired past "mirror slip" and has either replaced the adhesive with something that has raised the mirror higher from the mounting plate, or the mirror itself was broken and the replacement is too thick.

Here are some photos in case it helps:

I can't really verify either of my theories as I purchased from a shop and so cannot contact the previous owner. I also don't have another RX body to compare to and have struggled to find detailed reference images online to see if the mirror looks in the right position / thickness etc. The shop does provide warranty on the purchase and are going to take a look at it this weekend, but I thought I'd run my thoughts by you good folks here to see if I am totally on the wrong track or if I am along the right lines. The shop does have another RX body in stock which could be used to compare, and other C/Y mount lenses that could be tested to firmly eliminate the lens as the cause (although I'm pretty sure it isn't the issue). Thanks in advance for your thoughts!

 

[monopix]

Comparing to mine I'm not seeing any major differences but there looks like traces of glue along the bottom edge of your mirror so I think you may be correct in that someone has refitted the mirror incorrectly. The dealer should have checked the focus before selling it. Take it back.

 

[Zaxx]

Comparing to mine I'm not seeing any major differences but there looks like traces of glue along the bottom edge of your mirror so I think you may be correct in that someone has refitted the mirror incorrectly. The dealer should have checked the focus before selling it. Take it back.

Thanks for your thoughts. Honestly I was hoping you'd see it and chime in, given your website! One further thing I've noted is that the mirror will come down further than its automatic resting position if pushed gently with a probe. There's a smaller metal assembly with a tiny square mirror (for the spot meter / DFI perhaps?) behind the main one than clicks into place with a slight but noticeable resistance as the mirror is raised and lowered with a probe. I'm flying blind here so may be entirely insignificant.

The store does have a warranty and returns policy, so next step is to take it back to them, discuss the problem and see what can be done. I know Sendean Cameras in the UK service Contax film cameras, but have not used them before.

 

[jimjm]

It does appear from the photos that the mirror may be seated too high on it's mounting plate. I recently repaired this mirror slip issue on my RTSII. I noted that the existing adhesive was very thin before removing it, so I used a few strips of thin double-backed tape when replacing the mirror. Focusing has been spot-on and no mirror slip so far.
You might want to take advantage of their returns/repair policy if you don't want to touch the mirror yourself.

 

[monopix]

One further thing I've noted is that the mirror will come down further than its automatic resting position if pushed gently with a probe. There's a smaller metal assembly with a tiny square mirror (for the spot meter / DFI perhaps?) behind the main one than clicks into place with a slight but noticeable resistance as the mirror is raised and lowered with a probe.

Yes, the mirror stop is sprung so you can push the mirror down further if you try. The secondary mirror is for the focus indicator and it does flip into place quite smartly as the main mirror is raised or lowered. So that all sounds normal.

I would insist on a refund or replacement. Don't accept a 'repair' as you don't know what they might do. It might be possible to just adjust the mirror position to compensate but, if the mirror hasn't been fitted properly, it should be removed and refitted.

 

[Zaxx]

Just thought I'd give an update on where things ended up. The shop did take the camera back and conduct a repair. As suspected it was a botch job a previous owner had done to fix a slipped mirror.

The shop cleared off that mess and reattached the mirror properly, and now everything is working as it should be. Thanks again both for your help and advice!