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Mitchell type movement mirror timing

Aapo Lettinen

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Hi you all :)


I'm trying to figure out the exact timing of the mirror vs. the registration pins in camera using Mitchell type of movement and 170° shutter angle.

My camera is a Russian made Soyuz US3N so it is not a exact copy but close enough to some mitchells.


Generally, when are the reg pins supposed to engage in Mitchell movement and when they should retract compared to the mirror edge?


I have to be able to time this myself every now and then because of lubricating etc. so can't ship it to a camera tech. The movement should be in factory specs so no need to adjust it, so...


Are the pins supposed to engage just a tiny bit before the shutter opens so that the pins retract a moment before the shutter closes for film transport and the claws start to transport film a tiny bit before the shutter is fully closed, or...


...are they supposed to engage at the exact moment the shutter opens so that the shutter can fully close before film transport begins but the tiny moment the shutter opens may have some instability when the pins are centering the film, or...


...is the timing in the video about right? to me it looks like it is just a tiny bit off and the pins should engage just a tiny bit quicker after the shutter has passed to ensure the stability of the start of the exposure. but am I then risking instability at the end of the exposure?

This is pretty difficult trial and error to time because of the wormgear like gears used in the camera but I can live with a little off timing :rolleyes:





I also asked this at Motion Picture Technology group on Facebook, let's see what they think... :lol:

Edited by aapo lettinen
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The pins do look at bit early.

Can't you adjust the timing by loosening the mirror shutter and turning it anticlockwise a little ?


You could test it by shooting white dots on a black background on a short length of B&W 'stills' film and examining that.


John S :rolleyes:

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Since there might be a very slight movement as the pins engage but shouldn't be any when they retract I would shift the timing to allow the mirror shutter to cover the gate a little earlier to give some time for registration. But really, as long as the pull down phase of the claw is being covered you should be alright. I always used to check with film that had been marked with a sharpie squiggle to make sure that when I inched the camera over I couldn't see any motion when looking through the front.

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Thanks! I try to shift the mirror to a little earlier and see how it goes :)

I can hear a tiny noise and see the film move couple of hundreds of mm when the pins engage so there is clearly some pin registration going on, better to be sure that it is centered before shutter opens :)


I am using a battery drill as a motor at the moment, we am figuring out a rheostat motor solution with Olex but I can already do tests with the battery drill to adjust takeup tension etc and could also shoot tests with it when oct19 adapters arrive :D

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