Precision and Mechanical Shutter Speed Measurement

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They're using a Barnack body for the demo, but it's applicable to all focal plane rolling shutters.

It's meant as an entertainment piece, and I enjoyed it...

 

[robbie3]

My youngest son sent me this video yesterday, he knew I'd like it.

It was really interesting and I was very impressed by the quality and mechanical ingenuity of the early Leica body.

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In the era of cathode-tube TV sets, many of us used to check fast shutter speeds using the scanning rate of a TV screen (US: 60 scans a second; 50 scans for some countries). Same principle.

Of course, that needed the back door to be open (as in the video's test with a M body), so not quite as easy with a Barnack Leica.

Simple math - looking through the shutter opening at the TV, at 1/60th or longer, we would see the entire TV screen lit up.

At 1/125, we would see only half the TV screen illuminated; at 1/1000th, we would see only a narrow strip of activated phosphors glowing (1/16th the height of the screen); and so on for 1/250th and 1/500th.

Some folks used an audio turntable (at 78 rpm) with a white line taped on it, which worked for the slower speeds. Photograph the spinning turntable, and then see on the negative how much the line has blurred out during the exposure. At 1 second, the blur should cover 468 degrees (1.3 revolutions), and at 1/1000 sec, .47 degrees.

[Michael-IIIf]

I'm not surprised by the analogue stroboscope but I'm very impressed to learn about the team at https://www.camerarescue.org I'm checking out their website now.

What a find.

[M11 for me]

Absolutely great video. 

Isn't there one thing missing? 

What did they do now to increase or decrease the shutter speed after they found out the its working too slow or too fast?

[Anbaric]

Here is how the British Intelligence Objectives Sub-Committee reported Leitz's technique after their factory visit in 1946:

'The timing of the fast range of the shutter is carried out with the aid of a stroboscope of somewhat antique design. By means of this the 1/200, 1/500 and the 1/1000 speeds are checked. The stroboscope consists of a revolving drum placed horizontally, with 33 horizontal slits in its surface, illuminated from inside by a lamp of approximately 20 watts. The drum is driven by a belt from an electric motor which may be controlled by a rheostat. The drum is also coupled to a speedometer in order that its speed may be set. The correct speed for the drum to rotate at was 280 r.p.m. The camera is held on a wooden block in such a manner that the light from the rotating drum falls on the blinds of the focalplane shutter. The shutter is then fired and a series of stroboscopic lines are seen in the aperture. If the shutter is correctly set these lines appear vertically but if the shutter is incorrectly set the lines will curl down either to the left or to the right according to whether the shutter is set too slow or too fast. The checking of the lower speeds was only carried out on the 1/20 second and 1/4 second settings by means of a revolving series of lights. The various speeds of the shutter were not accurate to the measurements on the shutter control knob and this fact was acknowledged by the Leitz executives. who pointed out, however, that the results obtained were quite good enough for all general requirements. A metronome was used in checking the one second escapement.'

Edited February 28, 2023 by Anbaric