Re:cds cells and such

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Fri, 15 Nov 1996 01:49:05 -0500
>From: P3D romney <romney@xxxxxxxxxxxxxxx>
>
>Correction...I guess, as I said,  I really am not a  solid state expert,
>or I am suffering memory loss.  Sorry. I checked tonight and the Albrecht
>digital shutter tester uses an IR  photo diode or a photo transistor, not a
>cds cell. . You can get them at Radio Shack. As per accuracy of readout
>with a 10khz clock at 1/1000 sec. , it can be no greater than 10% since the
>digital display can only read 9.9ms, 10.0 ms 10.1 ms...etc..Nothing in
>between. See? The real trouble with shutter speed measurement is the
>brighter the light you use... the slower the shutter appears to be. This is
>on leaf shutters. This is because with bright light the digital timer
>begins to count when the blades are barely open and only stops when they
>are nearly closed. In dimmer light it might not gate until the blades were
>nearly open...Long ago they let shutters be 1/3 slow and still pass
>standards. Most 1/1000 second cameras were really about 1/700 sec. then. A
>1/500 sec Compur Rapid is really 1/400 sec, and the 1/150 sec Realist
>shutter would have been called !/200 sec. if sold  by a less reputable
>manufacturer than David White. Hope that helps...ED.
>

If you're building your own circuit you can design the digital readout to
show higher levels of accuracy. As to reading the timing of the shutter, you
could use a laser pointer as the light source and aimed so that the
measurment device only counts when the laser beam itself strikes the sensor.
Positioning of the laser and sensor would then be critical to accurate
measurement but if you're trying for a greater accuracy anyway, this makes
sense. I'm guessing but I think perfectly centered on the lens would be the
most accurate.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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