Wayne Shumaker wrote:
>
> At 12:04 PM 2/9/2000 -0500, Dirk wrote:
> >
> >I looked around locally and no one has this magazine. Without a printed
> >circuit board, it would be very hard to build this project.
>
> We build stuff all the time without PC board, we just cut blank copper
> circuit boards with exacto knife and route wires where needed. The
> circuit is straight forward, 1MHz oscillator into some counters that
> are gated by the photo diodes with amplifiers and comparators.
> Basically the two PDs gate a counter. You select different combinations
> to get shutter speed or curtain travel time. I will probably modify the
> circuit to use parts I have readily available. All the photo diodes I
> can find seem to be for infrared sensors.
>
Several years ago, I did this, but on an electronic 'breadboard'. Just
pop in the ICs, plug in some hook-up wire in the right places and you're
off. Well, OK so it ain't quite that simple. Point is, you don't need a
PC board. I've still got the thing breadboarded after all this time.
Mine is just like Wayne describes: a 1 Mhz crystal (giving 1 microsec
resolution) feeding enuf divide-by-10 counters to measure 1 second. Then
I used 5 hex displays so as to display resolution to 10s of microsecs to
be able to measure 1/2000 sec, which would display: 0.00050 if perfectly
accurate. I just used an LED for the ones digit.
I found the OMs to be quite accurate, though I don't have the data right
here. It was tough to accurately measure the 1/2000 speed. I don't
think I really got a good reading at that speed. At the time, my 'large'
format was a Mamiya TLR, with which accurate slide exposures were
problematic. This tester shed light on why: Some of the lenses (leaf
shutter lenses) were off by up to 50% at some shutter speeds. 1/2 stop
is a lot to slide film. I made notes of which lenses/speeds and used
them in the field to get better exposures.
I set up the tester by opening the back and placing the photodiode, with
a 'hood' on, there in the center, perpendicular to the curtain. Then a
light source in front of the lensless camera. Then test. It worked quite
well, though it only measures the 'slit' time. Measuring each curtain
time could be done by adding another photodiode and placing the 2 at
opposite ends of the focal plane opening. Then one could watch pulses
on a scope to measure both curtain times, or add another counter circuit
and switch the results to the display so you could see the exact travel
time of each curtain, as measured by the photodiodes. Of course, access
to the electronic signals which kick off each curtain would be more
exact.
George
> Wayne
>
>
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