How is parallax correction done in Leica M?

[cd95]

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I own leica MP & M2 for few years but I have no idea how the parallax correction/ or adjustment is done in these cameras. I know there is a swing arm that sensing the lens movement and then push the swing lens at rangefinder, and I guess it may make the correction at sametime, but I stil want to know more details of this mechanism. Can anyone give me some pictures or website link so that I can have a clear view of this machine? Thanks.

 

Charles

[UliWer]

Unfortunately I don't know an illustration in the web.

 

In his book about the Leica M Osterloh gives a good illustration of the viewfinder design and some explanations.(Puts in his Leica Compendium (1. edition) p. 193 just copied this illustration from Osterloh leaving out the explanations - Tao at its best).

 

You can get an idea of the design if you dismount the lens and touch the little roller you see on top of the camera's throat. Looking through the viewfinder when you touch it, you note that the frames move vertically.

 

Focussing the lens moves this roller which moves a little lens responsible for the rangefinder adjustment and at the same time it moves the mask for the lens frames vertically to achieve parallax correction.

[adan]

This is an x-section of the Leica M range/viewfinder (except that the original M3 had different geometry, with four right-angle bends in the RF light path (purple-blue line) instead of the zig-zag diagonal path used in the M2 et. seq.).

 

The framelines are formed by slits in a thin opaque mask, orange in this diagram, near the center.

 

As you guessed, the same lens/cam movement that shifts the RF double-image when focusing, also shifts the frame holding the mask, in a diagonal direction (top-left > bottom-right). You can see a part of the linkage as the silver levers with round tips, that attach to the frameline mask with black pins.

 

Note that the actual view of the world does not shift for parallax corrrection - just the lines themselves.

 

The mask for the framelines also has a rectangular cutout in the center, which is what forms the hard edge to the secondary rangefinder image (where the thick blue-purple line passes through the mask).

 

There are actually two masks sandwiched tight together, which shift relative to one another via a different link to the lens preview lever and to the lens mount. As they shift, they reveal or hide different framelines, so that mounting a 50mm lens hides the 28/35/90/135 lines and reveals the 50/75 lines, and mounting a 90mm lens hides the 35/50/75/135 lines, and reveals the 28/90 lines, etc. (Your M2 simply has masks with fewer slits, thus no 28/75/135 lines).

 

There is a curved mirror (red arc, center) that captures light coming through the frameline illumination window (serrated) and shines it through the slits in the masks (yellow light path). It also has a hole in it to allow passage of the rangefinder secondary image.

 

As a side note, the RF image is shifted for focusing by movement of the black cylinder holding two small lenses, which swings at the end of the copper-colored arm attached to the RF cam (gray wheel partially visible under the pale purple "L", center). This is the only glass that actually moves within the viewfinder, for either focusing or parallax correction - all the rest of the glass (pale shades of blue) never moves.

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[cd95]

Unfortunately I don't know an illustration in the web.

 

In his book about the Leica M Osterloh gives a good illustration of the viewfinder design and some explanations.(Puts in his Leica Compendium ...

 

Thank you for your explanation, actually I have one of Osterloh's book "Leica M, Advanced photo school", but I cannot find a clear enough drawing of this mechanism because I'm really interesing to this mechanism. Hopefully, someday I can open my Leica M to see how it works exactly.

 

 

 

This is an x-section of the Leica M range/viewfinder (except that the original M3 had different geometry, with four right-angle bends in the RF light path (purple-blue line) instead of the zig-zag diagonal path used in the M2 et. seq.).

 

The framelines are formed by slits in a thin opaque mask, orange in this diagram, near the center

....

 

Thank you for your detailed explanation and picture, it helps to understand Leica rangefinder mechanism. Please find my picture below and correct me if I make any stupid mistakes (I download it long time ago from web and I forgot where it was from, this is the best picture I could find I'd like to thank the owner firstly). I marked the picture with some letters so that I can explain my understanding:

 

As you can see the roller "A" rest on the lens cam, it pushs the lever "B" (by a arm) wich pivoted on "b-b", lever "B" then pushs the swing arm "C" who is pivoted on "a-a" and carry the rangefinder lens and a screw "S"; The frame mask, I guess, is driven by this screw "S", is that correct? Then when we focus the lens, the rangefinder lens swings and at meantime the parallax correction is made by A---B---C---S---frame mask, is that true? Thanks.

 

Charles

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[Guest Ornello]

I own leica MP & M2 for few years but I have no idea how the parallax correction/ or adjustment is done in these cameras. I know there is a swing arm that sensing the lens movement and then push the swing lens at rangefinder, and I guess it may make the correction at sametime, but I stil want to know more details of this mechanism. Can anyone give me some pictures or website link so that I can have a clear view of this machine? Thanks.

 

Charles

 

With mirrors