I have recently purchased a new M6 TTL, together with a 2nd hand 50mm summicron (4th version), and I've noticed a slight problem after using it today. When I try to focus things at infinity, the two images won't line up exactly, it is ever so slightly off. If I gently force the focusing handle, then it'll be in perfect focus (the infinity mark on the lens barrel is about 0.5mm off the arrow when fully turned). So is this a problem with my lens? Or is the RF alignment out? How would I go about fixing it?

Thx for any info.

-- Daniel Gonzalez (dg@hotmail.com), December 21, 2001

Answers

Try another lens first. Preferably two or three so that you can isolate the problem to the body or lens. Most of the time it is the body that needs a minor adjustment but I once had an old 50/2 that needed its focus cam adjusted. The adjustment is very simple to do and it has been covered many times in past posts.

-- John Collier (jbcollier@powersurfr.com), December 21, 2001.

Who lives there. Check to see and make sure the focus is on at close distances and wide open that is the important thing because of the depth of field. At infinity you should always be in focus because of the DOF.

-- Al Henry (J Henry@provide.net), December 21, 2001.

Al, you may be wrong about the close focus--if your infinity focus is right, then so is close focus. To make sure ifinity is correx, focus on a object about 3 miles away. I always use clouds (the ones in the sky).

-- Steve LeHuray (icommag@toad.net), December 21, 2001.

Steve is right in general, assuming the camera left the factory properly adjusted. Normally it's the infinity focus that goes "out" from bumps, but there *is* an additional close-focus adjustment. Even in a CLA most of the time they don't have to do anything with that adjustment. However anything can happen with final assembly and I wouldn't just assume the close adjustment is spot-on without checking. However it's not as easy to do at home as the infinity test. While infinity is a dead stop on the lens, the close distance markings are more approximate than you'd suspect and not always easy to perfectly lie-up with the index mark. For example, at the "10ft" setting, where is 10 ft? At the "1", the "0" or exactly in-between-- and how to be certain you're "there"? The only way is to put a ground glass in the film plane and measure to your target.

As to the comment that infinity can be "off" and covered by DOF, that is faulty logic with a rangefinder because is=f infinity is "off" the rest of the distances will be "off" also.

-- Jay (infinitydt@aol.com), December 21, 2001.

I rather use far away posts, like those of telephone lines on electricity, those are so thin that it is easy to check misalignements; Steve I have try to do it with clouds, but I feel it may be too fuzzy.

-- r watson (al1231234@hotmail.com), December 21, 2001.

Hi Steve. You are correct.However if the lens is in focus at the extreme end of the rotation of the focusing ring then the onlt way I know of to line up the markings on the lens barrel with the ring.would be to disingage and reset the ring or rotate the helical in ither case it will effect the near focus at wide appiture. Then the error will be shifted to the low end of the distance scale so instead of the distance being exactly three feet at the close extreme it might be 35.67"or whatever, no big thing at F2. Then again who uses scale focusing.You pick where you want the error.Because its always going to be there even if you split the difference.

-- AL Henry (J Henry@provide.net), December 21, 2001.

That's not necessarily true, Al. You're assuming there's no error right now at close distances, which is probably not the case. More than likely the whole thing is off. I say this only based on the types of system involved, which make it much easier to slip the whole range off than just one end of it. My nomination, however, is that the lens is probably fine, and the camera's off. Try a couple of other lenses, first.

-- Michael Darnton (mdarnton@hotmail.com), December 21, 2001.

You mentioned that you had to force the focus over to the infinity position. It could be the lens, or it could be that the focus cam-follower (the little wheel attached to the arm assembly in the camera, which rolls on the lenses' focus-cam), is impeded in its inward movement. You might try removing the lens from the camera, and very gently pushing in this follower while viewing a distant scene through the finder, to see if the rangefinder will line up at infinity. If it does, then there may be a "flat-spot" on the lenses focus cam. Good luck!

-- John Layton (john.layton@valley.net), December 22, 2001.