Contax IIIa rangefinder and lens adjustment. HELP.

I checked my Contax IIIa today and found the rangefinder to be in

adjustment. I measured 2 meters and placed a target from the camera

film plane. Set the helical to read 2 meters and the rangefinder was

dead on. I set the camera to "T" and placed a frosted tape across the

rails on the the film plane. When I took the loop and viewed the

target it was a bit fuzzy. When I fine tune adjusted lens to the

target the helical read 2.6 meters. I tripple checked and got the same

reading. The lens had to be moved to the film plane a small amount to

be in focus, and what my question would be is how much? I don't know

if I have to shim helical out or remove shims. I tried to loose the

lock screw on the lens barrel but to no avail. I am thinking that I

will have to remove shims. I don't want to mess with the locking screw

on the lens barrel, it seems to be frozen. This is a Sonnar f/2 50mm

If worse comes to worse I could drill the screw at the machine shop

and rethread with a new one. Are there any suggestions?

Check out this site: http://www.zeisscamera.com/

 

From your description, the entire lens mount on the camera needs to move. That lens mount is attached to the body casting, and is spaced by shims. There is probably nothing wrong with the lens, but to be sure, you should mount another lens onto the body and see if it focuses.

 

The whole trick is to see which needs adjustment, the body or the lens.

 

 

...Vick

If your numbers are correct, my guess is that your lens mount needs to move back about 0.3mm.

 

It would be a good idea, though, to check the focus at infinity. You can use a second camera to do this accurately, as shown at http://rick_oleson.tripod.com/index-123.html .... when working at infinity, you don't have to be concerned about the accuracy of your distance measurements, or of the engraving on the lens mount, or just where they wanted you to measure to. Of course, at closer distances, you still want the rangefinder to match the lens - but unless you're ignoring the rangefinder and focusing by the numbers, the match between the rangefinder and the lens is more important than the engraved numbers, except at infinity where the lens locks in.

The rangefinder does not match the focus. When the rangefinder is lined on the target the lens is a wee bit out of focus, enough to make a distinctive difference. I checked the focus with my Kiev 88 at infinity and the contax is off. the split image showed a shift of the target. The lens need to be colimated. Two ways can be applied as I found out today with my Kiev 4m, by moving the lens in the barrel or shifting the Helical. Either way will give the 35mm required for a perfect focus. I am hoping that the helical is shimmed, and thereby removing the proper amount of shim should put me back on track. Right now the focus distance excedes the rangefinder distance at 2 meters by 0.6 meters. With a good DOF it would not matter. The photos that I have posted show reasonable good focus.

http://www.photo.net/photodb/folder?folder_id=518233

as you can tell. I am slowly understanding what is going on with proper focus adjustment with a rangefinder camera. I shot a short roll of B&W this afternoon with the kiev 4m after final adjustment and was well pleased with the results.

Its difficult to get tape to lie flat on the inner rails without some sort of sag leading to error. Better to use Rick's method of an SLR and a ground glass target to check collimation at infinity.

 

Shimming the lens mount is a very tricky business. I would only do this if you are absolutely certain that the lens is properly collimated. I've shimmed lens mounts using a depth micrometer to measure all four corners to the top of the film, held in rigidly. Do not rely on the pressure plate to be rigid.

 

To improperly shim a camera to match a miscollimated lens is not a good thing because it will not work properly with any other lens. Try a drop of solvent on that screw. It may be held with some paint or threadlocker. Or try a hot, fine tip of a soldering iron applied directly to the screw.

Do you have another lens to check on the camera? You really want to be sure whether the error is occurring in the lens or the body before making any changes, or as Mike said you'll wind up with a camera that no longer accepts interchangeable lenses. Might as well have a Canonet at that point.....

 

:)=

I will take the camera to the machine shop and have it checked for proper depth form the film plane to the lens collar. This I understand must be 35mm + or- a wee bit. I have it written down somewhere. Had my Kiev 4a check the other day, had to shim it a bit to get proper distances. I will try to free the locking screw after checking the helical distances. Does anyone know how the cover plate on the helical is mounted. I see only two screws on the bottom. Is this the only two to be removed. Does the top cover need to come off to remove it?

 

I place a piece of frosted tape on the top film rail and press it down the I will strtch the tape to the bottom rail snug and have never had any problems with any sag. If you are careful it's easy done.

Make shure you really understand where the film sits when the rear cover is closed! Shimming the lens mount on a Contax RF is not an easy task! Tape will work but it must be taught and placed on the same rails the film sits.

 

I believe some test shots of a tape measure at max aperture would be a cheap check..rahter than a $200 CLA!

Flange to film plane is 34.85mm +/- 0.01mm on the Contax RF. (or more practically about 0.025mm on the tolerance, 1/1000") How accurate do you really think you are with the tape? Within 1/1000 of an inch, I don't think so.

 

I'm telling you, collimate the lens first because is a rare thing for a Contax to have the mount wrong, especially if there is no evidence of it having been serviced before.

 

That distance is measured to the top of the outer bayonet lugs by the way, but you need to measure from the top of the mount and subtract the difference out.

If the RF is dead on on a 2.0 meters far target with the helical set at 2.0 meters then the camera by itself has no problem, and the problem is with the lens collimation, for sure. Don't do anything to the camera, in any way.<p>

 

Now you have to do what is described <a href=http://host.fptoday.com/melek/zeiss/repair/sonnar-clean.html>here</a> followed by what is explained <a href=http://host.fptoday.com/melek/zeiss/repair/collimate/collimate.html>there.</a><p>Or just find another lens, if this one has a frozen screw (I'm not too sure, what screw you're talking about, regarding what is a postwar 2/50 Sonnar according to the picture of your camera) so that you cannot dissassemble it. Good luck.

1) Ensure the rangefinder has been calibrated. I believe I e-mailed you instructions. This is where everything starts. If your rangefinder isn't calibrated, everything else will be off.

 

2) Ensure the lens is properly collimated. That is, it should achieve correct focus when the helicals reaches infinity. Not before. Check collimation with an SLR. There are instructions on the Web, as well as my own site.

 

3) Check focus with ground glass, if possible. Scotch-brand Magic transparent tape should be OK, as long as its stretched taught across the film rails (sounds like you've done this). As others said, ignore the markings on the helical, and use the rangefinder image as your guide, comparing it to what you see on the tape.

 

It's possible that you may need to adjust a small part in the rangefinder system. It's a little known part, but it's something I discovered while working on a camera that had been declared, "it's as good as it's going to get," by another noted repairman.

Finished after 6 hours. I checked the helical flange to film distance it was dead on factory specs. The next thing I checked was target at infinity. I used a clear plastic with target drawn on inside where the emulsion would be. It showed on the split image on my Kiev 88(which takes razor sharp images) miss alignment of a vertical line drawn on the plastic. The top was shift to the right This told me the focal distance had to be shortened. While I was set up I used a frosted tape carefully placed tight across the film rails (not the pressure plate rails). Then I set up my horizonal lines target (supplied by a good friend) at a distance of 2 meters. The reason two meters is that I can just make out the fine lines on the target at that distance. I proceded to dissamble the lens very careful and found instead of a shim there was an adjusting ring to set for a shim. I screwed it inward two full turns reassembled and checked. now instead of 2.6 meters at focus it was now 2.3meters. disasembled again two more turns and Wala...Dead on. Set up the two cameras for infinity check, split image (horizontal) cut the vertical line drawn on target and Walla Walla. dead on. Cleaned up mess and loaded film. Now i'm too tired to shoot anything. Will tomorrow. Now I have one more camera to check. My kiev4am. I think that is what it is(no meter). Thanks all you fellows I don't know where i'd be without you-ez guys. Thanks millions.

Did you check the lens at infinity with your kiev 88? I use a glass plate and take into account the thickness of marjed area on the film rail. I use a sonnar 300mm/4 with kiev 88cm.

 

Richard