Contax 159mm erratic aperture display

naaldvoerder · Joined: 06 May 2011 Posts: 15

I have a donated Contax159mm that needed cleaning of the release magnets. I cleaned them easily enough, and the shutter fires, but the camera shows some erratic behavior. When I attach a 2.8 lens and stop down,the display will show the correct aperture until 8.0, but when stopping down beyond that the displayed aperture will be bigger again. So 11 will display 5.6, 22 will display 4.0. The suggested shutter speed will correspond with the erratic displayed aperture. When I mount an 1.4 lens the same phenomenon occurs, but then from 4.0 onwards. Can any one of you shed some light on this strange behavior?

Thanks.

Gardener · Joined: 22 Sep 2013 Posts: 950 Location: USA

If you are lucky it's just a short of some sort. Typically the spring-loaded lever that engages the aperture moves a brush over a contact plate. On some camera it sits directly under the mount and is fairly easily accessible for cleaning. Some camera manufacturers were complete a-holes about it - I believe it is some of the Olympuses that utilize a system of pulleys with actual reading done under the top cover plate.
Bottom line is - you might need to open things.

monopix · Joined: 07 Feb 2010 Posts: 32

You can get the 159 service manual from this link

https://drive.google.com/open?id=0B4O3Tuo7UDz3d1o1M29rLU9VZW8

If you look at page 72 you'll see a list of possible reasons. But my best bet is the aperture code wheel has a bad contact. Essentially what Gardener was saying. The wheel is on the side of the mirror box and is geared to the aperture ring that surrounds the lens mount. You can just about see it if you remove the base plate and the cover that surrounds the bottom of the lens mount. It's on the right hand side looking from the front. You might just get some contact cleaner under it but you won't be able to do anything else without further dismantling.

One thing to note is the aperture ring tells the body by how much the lens is stopped down. It doesn't indicate a specific aperture. The aperture to display is calculated from the maximum aperture and how much the lens is stopped down. That's why the behaviour changes with different lenses. But in both cases the problem starts after you have stopped down three stops.

naaldvoerder · Joined: 06 May 2011 Posts: 15

Excellent! I took your advice and dug into the camera. I found an broken track on the aperture code wheel. I was able to solder on a wire bridge. Now i have trouble putting the mirror box back into the camera. The repair manual states; Charg shutter and mirror box assembly, but doesn’t tell me how. Can you help me with that?

monopix · Joined: 07 Feb 2010 Posts: 32