Confusion regarding the mechanics of rangefinder calibration

[Cam_Han]

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How does turning the hex screw on the rangefinder coupling arm roller alter the position of the rangefinder patch at infinity focus? There seems to be no gearing connecting the screw to the rest of the rangefinder system.

Edited July 26, 2023 by Cam_Han

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[jaapv]

As it is an eccentric it will alter the position of the arm in relation to the helicoid of the lens.

[adan]

14 hours ago, Cam_Han said:

There seems to be no gearing connecting the screw to the rest of the rangefinder system.

Exactly - because all the magic takes place on the hidden side of the roller, where it connects to the lever.

Sometimes a picture is worth 1000 words.

This schematic shows the camera's RF roller we all know and love, with some X-ray vision (and slight exaggeration).

The roller is two parts - a central hub or "fat axle" - with the hex-key hole in the center. And the outer rim that is free to slide around the central axle (to minimize and equalize wear).

The entire roller (rim and hub) is attached to the rangefinder's lever on another axle (red circles) - which is off-center on the hub (i.e. ec-centric)

When you insert the hex key (or in older Ms, a slotted tool) and twist the whole roller on its red axle (note the orientation of the hexagon), it may appear to simply turn around the center of the hexagon. But it doesn't - it turns around the red axle's center, behind the scenes!

Since the center of the hex-key hub is not aligned with the center of rotation (red axle) - that moves the roller in and out of the camera (in this diagram, up and down) by tiny amounts. That changes the distance between the edge of the roller touching the lens (the three different black phantom lines at the bottom), and the fixed point where the red axle connects to the RF lever (red central line through the red circle), by small fractions of a mm.

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[Cam_Han]

On 7/27/2023 at 12:54 AM, jaapv said:

As it is an eccentric it will alter the position of the arm in relation to the helicoid of the lens.

Thanks for the explanation

[Cam_Han]

On 7/27/2023 at 3:17 PM, adan said:

Exactly - because all the magic takes place on the hidden side of the roller, where it connects to the lever.

Sometimes a picture is worth 1000 words.

This schematic shows the camera's RF roller we all know and love, with some X-ray vision (and slight exaggeration).

The roller is two parts - a central hub or "fat axle" - with the hex-key hole in the center. And the outer rim that is free to slide around the central axle (to minimize and equalize wear).

The entire roller (rim and hub) is attached to the rangefinder's lever on another axle (red circles) - which is off-center on the hub (i.e. ec-centric)

When you insert the hex key (or in older Ms, a slotted tool) and twist the whole roller on its red axle (note the orientation of the hexagon), it may appear to simply turn around the center of the hexagon. But it doesn't - it turns around the red axle's center, behind the scenes!

Since the center of the hex-key hub is not aligned with the center of rotation (red axle) - that moves the roller in and out of the camera (in this diagram, up and down) by tiny amounts. That changes the distance between the edge of the roller touching the lens (the three different black phantom lines at the bottom), and the fixed point where the red axle connects to the RF lever (red central line through the red circle), by small fractions of a mm.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Wow that is amazing! Thank you!