Rangefinder calibration

[robertcambab]

I am curious as to how I can check the calibration of my IIIf rangefinder mechanism. Also I have been told that it is relatively easy to adjust, i.e the screw by the viewfinder window is removed and the adjustment screw can be reached relatively easily from there. Your comments and help would be appreciated. In addition, my Bessa 3A took some hellish abuse at the hands of baggage handlers at Glasgow airport some time ago, which has just come to light. Is there any UK repair people who can put this right.

Many thanks,

Robert.

 

[John Shriver]

The adjustment behind the screw on the front is for zeroing the rangefinder at infinity. You need a lens whose rangefinder cam is known to "be correct", and protrudes exactly 7.5mm when the lens is focused at infinity. (You can probably assume this of any properly assembled 50mm Leica lens.) Canon made a dummy lens for doing this adjustment.

Then set the lens to infinity. Point the camera at something at least 1/4 mile away. The moon is handy for this at night. Adjust the small screw for horizontal alignment of the rangefinder.

Of course, this doesn't check that the lens flange is the right distance from the film, that the lens is collimated, or that the "rate" (gain) of the rangefinder is right. But it's the adjustment that is most likely to "go out", which is why they made it so accessible.

 

[robertcambab]

Hi John,

Does the horizontal alignment sort the calibration?

Regards,

Robert

 

[John Shriver]

The horizontal alignment is the most frequently needed adjustment. Vertical alignment also has to be right, it is effected by rotating the glass wedge in the front round window over the lens. There are notches in the retaining ring you use to turn it.

(The rate/gain is adjusted by changing the effective length of the arm with the roller on it. The film-flange distance is adjusted with shims under the lens mount. Both are much more stable adjustments.)

All the calibrations are important to accurate focus. It's just that zeroing out the infinity is the most commonly needed one.

 

[colyn]

The proper way to calibrate the rf is to setup the camera 1 meter (film plane) from a test chart or some other object that can be sharply focused with the rf. Focus till the rf shows proper focus then check the focus scale on the lens. It should be properly lined up with 1 meter. If your lens does not focus in meters then used this. 1 meter = 3.2808399 feet

 

[robertcambab]

Thanks people, very useful comments. I will see if there is a video tutorial on the subject. Is there such a thing?

Many thanks,

Robert

 

[VictorM.]

There's always Leica Repair Club: http://www.mediajoy.com/en/lrc/lbal/index.html