What's the best way to check if a lens couples correctly to the cameras rangefinder? Is it enough to see if the rangefinder is perfectly focused when the lens is at infinity? Is it hard to adjust?

-- Thomas Krantz (tkrantz@kpmg.com), November 23, 2001

Answers

The M camera's rangefinder is set with the infinity setting and then checked at 10 metres and 1 metre. Most of the time the infinity setting is all that needs to be adjusted. The infinity setting is made by turning the eccentric screw holding the roller to the rangefinder arm. Remember infinity is a LONG way away. Use an object at least 3km distant. After the infinity setting is made, check the focus at 10 metres and 1 meter using either a ground glass screen against the film rails or expose and develop test exposures at those distances. If everything is fine, pat your self on the back and congratulate yourself on a job well done.

If your close focus is off, then you need to adjust the length of the rangefinder arm. The arm is attached to the shaft that goes up into the viewfinder mechanism by an eccentric pivot. There is a lock screw and a adjusting fork. Making the arm longer, reduces the rotation of the shaft for a given lens cam movement; and, making the arm shorter increases the rotation of the shaft. If your actual focused point is farther than your rangefinder's point of focus then shorten the arm. If your actual focused point is closer than your rangefinder's point of focus then lengthen the arm. After every arm length adjustment, you need to reset the initial infinity setting again before doing any more checking.

It is also possible that your lens is out. NEVER adjust a camera based on one lens. Try several lenses to make sure your lens is not the problem. My M2 was bought used with a 50/2. As I added lenses, I found that I could not get a consistant infinity setting from lens to lens. It turned out to be the 50/2 that needed adjusting.

Make all adjustments carefully with only force applied in the direction you want the adjustment to move. DO NOT PUSH AGAINST THE SCREW BEING ADJUSTED. Make sure your screwdrivers fit. Sloppy fit will lead to damaged screws or the screwdriver slipping off!

If you get reular CLAs then it is usually only the infinity setting that needs tweaking. Older cameras may need both adjustments or even more (there are adjustments for each individual frameline mask set as well) If you are not comfortable with tweaking your Rolex, then leave well enough alone! A Leica Tech has special jigs and tools which enables them to get it much closer to spec than we can in the field. It only takes them about a half an hour and is not that expensive. I limit myself to the infinity setting and let my repair tech do the more involved arm length adjustment.

-- John Collier (jbcollier@powersurfr.com), November 23, 2001.

As for me the best way to check the correctness of lens-RF coupling is using a ground glass on a film gate.

At first measure with an indicator measurer (0.001mm) the lens flange to the film plane distance. Make it absolutely exact: 28.8mm for SM- Leicas and 27.8mm for M-Leicas.

For M-Leica’s the thickness of the ground glass is about 0.8-1.0mm that make it easy to insert into the film channel. Take off a back door at all, squeeze a camera body slightly from both rounded short sides to spread a film channel split and insert with no force the ground glass in it. Use a tripod and a loupe.

For SM Leica’s (only IIIC, IIId, IIIf, IIIg): take off a body shell (unscrew 4 front screws and 2-4 ones on the upper plate, pull down the body shell, be careful to damage a vulcanite near slow speed disk ) the thickness of the ground glass doesn’t matter. In that case when the camera bottom is off and using a tripod is impossible, you have to keep a camera in hands with a ground glass slightly pressed to film channel rails, though you can use a ‘scotch’ to glue them together. Use a x4-6 loupe.

Then focus a lens full open on a subject/marks previously placed at exactly measured distances beginning from 1.0 (0.7/0.9) mtr to infinity. At first for focussing use the ground glass, then RF, compare both settings on a distance scale of a lens, use a ruler, record a difference, then analyze records. If the tolerance is in limit of the DOF (full open) for the lens treasured, the lens mates with the RF O’K.

Hope this help.

-- Victor Randin (ved@enran.com.ua), November 23, 2001.