Shutter Speed Testing 16mm and Spy Cameras (In Which The Back Cannot Be Removed)

ic-racer

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Shutter speed testing cameras in which the film back cannot be removed presents somewhat of a challenge. Frequently a reflective surface is placed at the film plane and a light is reflected off that surface through the lens and the light emminating from the lens is picked up by a sensor in front of the camera.
 
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ic-racer

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An Autocollimator, projects an image through the lens of a camera and the light reflected back is witnessed via the eyepiece.

It is not much trouble to simply connect the sensor of a shutter tester to the eyepiece of the device to measure shutter speed.

 
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ic-racer

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A reflective plate, made of polished brass, is placed in the film channel of the camera.

 
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xkaes

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Very interesting stuff.

The good news is that the shutters on these "simple" cameras are usually pretty robust.

One way to test a submini shutter -- without any special technique -- is to compare the results to a known good shutter. Let's say you have a reliable 35mm camera. Takes shots of a gray card with the 35mm camera at the same speeds (and f-stop) as the submini. Then do the same with the submini -- using the same film. Develop both films the same and see if the densities are the same. You can use a densitometer if you have one, but your eyeball should suffice.
 
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ic-racer

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The camera is placed under the Autocollimator with the beam directed at the shutter opening.

Releasing the shutter triggers the shutter speed tester.

Typical results from one of my Minolta 16 cameras that has never been serviced:

#751555

1/30 = 1/20 + 0.5EV
1/60 = 1/40 + 0.6EV
1/125 = 1/80 + 0.7EV
1/250 = 1/263 - 0.1EV
1/500 = 1/305 + 0.7EV

 
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4season

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Clever! I had figured out the trick of collimating the Mamiya-16 Super on my own, but not how to measure shutter speeds.

In lieu of scoring a purpose-built autocollimator, I may fabricate one using a modified film back on my Canon F-1 or Nikon F. In Let's Try! Repair and Maintenance of Cameras, Michio Ozeki provides details of such a project. Not a new idea, I recall seeing film backs for sale which were missing their pressure plates, and which had a film-sized cutout, and never knew what they were for. But now I know.
 
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ic-racer

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Yes, it shouldn't be too hard to make an autocollimator.

I don't know if you know, but the Minolta 16QT has a hole in the back (hole in the pressure plate too).


I was looking at old reflector telescopes as a starting point. In fact this one is on ebay for $10 (center picsture). It might make a good starting point. Replace the little flat mirror with a 50/50% semi-silvered mirror and replace the main mirror with a convex lens.

 
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