I think that is a very valid thing to do - at the end of the exercise it is the actual photographic exposure on the film that really matters - not the theoretically calculated exposure based on a moving slot. So - Photographic testing has to be the benchmark. My problem is that the 'old' anniversary graphic focal plane shutter has 24 seperate shutter speeds to test. So that's a whole box of film to to check each speed just once!Originally Posted by jnanian
Do the equivalent of shooting test strips. One shot with the dark slide 1/4 out, another 1/2 out, and so on.
Steven, I ended up making an orifice in a block of wood. I made the opening with an .040 drill bit, which is near enough 1mm. I then drilled a 1/4" hold in each side, one to hold the photo-transistor (with black tape around it to block extraneous light), and one to open up the snout end a bit. The orifice ended up being about a quarter inch thick, in front of the transistor. I used a 6-volt lantern to provide the light source, and that was pointed straight into the tester, and moved back enough (with the o-scope in free running mode) to drop the voltage a bit, ensuring that the photo-transistor was not saturating. The position of the light changed between tests, which changed how much light was getting down that orifice. That accounts for the different voltage levels between different speeds.
Of course, my main purpose was to make sure that the shutter didn't need further rebuilding or some other repair, while the camera was still sitting on my work bench. And I wanted to make sure that I at least had probabilities in my favor when committing film to the final test.
Rick "who'll probably do a final test with Fujiroid, which is usefully narrow in addition to being quick" Denney
Except as an academic exercise why test all 24 combinations? I can't believe that there can be that many variables- for example there are four[?] slit widths which are constant no matter what the spring tension. Design of the experiment using statistical methods is beyond my experience, but I'd bet a roll of 620 verichrome that less than say 12 tests would cover it- probly 6 ??. With some darkslide trickery as Dan suggests that's only 3 or 4 sheets of film [if that, maybe]. Then there are those combinations that one probly NEVER would use. Take heart!
I don't think it is necessary to test each combination in sequence one at a time. I was just pointing out the complications of the early shutter. One problem, of course, is that because the curtain is a single long curtain with several slots in it - just winding to a different slot always changes the spring tension as well... There are always two variables changing.
Remember, my shutter has had a complete strip down and rebuild by an amateur (me!) so it may or may not now be working well.
A few tests might indicate if it was working correctly - but if you have delusions of using the zone system (!) - what you need is consistency. It doesn't matter if a particular speed is, say, 20% slow - as long as it is ALWAYS 20% slow - so it would be nice to be able to test a particular speed half a dozen times or more to see if it is the same each time.
Also, if the shutter has been used at 1/10 second for the last 20 shots (low tension, shutter cloth all nice and loose...) when you crank it up to 1/500th or 1/1000th - will you get the same speed as when the shutter has been fired a few times on high tension and the shutter is nice and tightly packed? Or visa versa?
Those are tests I'd rather do with a bit of blinking electronics than by shooting and developing film! I think it is at this stage that you either waste a lot of film or sally forth with a shutter that might - or might not, be working properly (and possibly still end up wasting film and photo opportunities!)
Once I've decided the shutter is indeed working properly and is reliable and consistent - yep, I reckon you could then calibrate photographically it with a few sheets of film.
I think that is a very valid thing to do - at the end of the exercise it is the actual photographic exposure on the film that really matters - not the theoretically calculated exposure based on a moving slot. So - Photographic testing has to be the benchmark. My problem is that the 'old' anniversary graphic focal plane shutter has 24 seperate shutter speeds to test. So that's a whole box of film to to check each speed just once!
i see what you are saying steven .. it sounds like a fun exercise
you might consider cutting your film in half and sticking them film holders
that way to save you some $$, it's like doing a test strip, instead of a test print...
with an old camera sometimes the springs aren't as springy and governors don't
slow stuff down like they used to ....
i just say well a 40th is the best the shutter can do at a 60th of a second,
instead of trying to get everything just-perfect. it seems to work OK for me
This repair is beyond me, but I have one of these machines that I bought in fairly decent shape. I was wondering how you go about testing the shutter speed.
How good are you with wiring up simple circuits?
The overall conclusion of this thread might be that the audio program 'Audacity' - combined with a little bit of basic electronics and mounting the phototransistor behind a pinhole and you can get pretty reasonable readings up to 1/1000s.
Very, very minimal wiring and just holding the phototransistor behind the shutter - and you can only get up to about 1/200 sec.
I've just come across this very interesting thread whilst searching for information on shutter speed testers.
I'd particularly like to try Steve's Improved Cascode No. 2 circuit, but am puzzled about how typical small signal NPN transistors like the ones suggested can function as photodiodes. I'm no doubt oblivious to the 'bleedin obvious', but if someone can enlighten me I'd be very interested to know.
Also, what typical output voltages should we expect with the resistor values shown and a 4.5 volt supply?
Thanks,
Barry.
Q1 in the schematic is the phototransistor. It is denoted with the three slashes to the left of it. I'd guess that you would get close to your supply voltage out of the circuit, but you can test it.
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