I was looking at some diagrams of an electronic shutter speed timer to measure the actual speeds. I was thinking that it might be easy to just modify a digital stopwatch so that a light sensor replaces the start/stop switch. Stopwatches only count 1/100th seconds, but at least one could test out the slower speeds. Any help from you electronics guru's would be appreciated.
Not exactly an answer to your question, but related to this issue anyway. I’ve devised a quick and cheap method to test the slow speeds on my lenses using my desktop computer. Hardware needed: a microphone. Software: a wave editor. Record the sound of the shutter firing at different speeds. Save them as wave files. Inspect them on the wave editor and note the time interval between the 2 peaks (the opening and closing of the shutter). Usually wave editors record times in 1/1000 of a second so you have enough precision for the slow speeds. I was able to get meaningful data up to 1/30, after that it becomes hard to identify where the actual peaks are.
The Calumet shutter tester is pretty much the same design as you are thinking about, although they have a finer granularity and accuracy. Of course, they cost $100. If you could come up with a $20-$50 design, you might have something.
Slow speeds are pretty easy, it's the fast speeds that are a bitch. The link to the tester that Steve Baggett posted is probably the best $100 equipment investment you can make, and the only $100 investment that'll give you peace of mind...
You can always split the cost with a buddy. Unlike a meter or a tripod, a shutter tester isn't the sort of tool I'd need in the field very often.
There are a couple of ways to check the shorter times that are cheap and easy. One is to use a record turn table at 33-1/3rpm. Put a white line on the table and with it running take a picture at each speed. You then measure the angle the line moved and calculate the speed. The other is to photograph your television set. The screen is scanned by the tube about once every 1/30 th second. This allows speeds from 1/60 and above to be tested. You take a picture and count the lines it records. I don't know the exact count but it should be out there on the net somewhere.
I've seen a lot of different designs on the 'net.
I tried to do one, which was a soundcard-based solution. I had two problems. I couldn't find either the phototransistor specified (or any reasonable replacement) or the resistor. I was finally able to get a number of sample resistors, I believe 5k Ohm, which I got with a .1% tolerance.
The phototransistor, however, has plagued me to this day. I've tried a number of scrap ones, but none worked.
I think that eventually, I'll get the right phototransistor and circuitry, and make one that's BASIC-stamp based. I'll want something that works with all shutters, and goes from 10 seconds down to about 1/1000 or shorter.
I'll keep you guys posted if I make any progress. Also, if any of you know of the source of phototransistors, I'd appreciate the info. Thanks.
Jason, an extensive search for a 5k resistor is not necessary - just get the closest higher value you can (5.6k in the E24 series if memory serves). Anything between +/- 50% or more would probably work. Ditto the phototransistor/photodiode - any one with a widely similar response would probably work. Problem, is, most are Infrared, not visible light, sensitive so you need an IR LED too. Any hobby electronics store (Radio Shack/Tandy in the US or Maplin in the UK) should have something suitable. Have a search for light activated switch circuits that use photodiodes and cannibalise the relevant part of the circuit.
I find a microphone plugged in to the PC and software such as SoundCheck which displays the waveform graphically with a time scale on the x-axis works to approx 1/125th second. The waveform can take a bit of deciphering, but by comparing a few at different speeds you can see where the shutter is fully open and when it closes. At these slower speeds, the open/close times will not materially effect the exposure times - or you can extrapolate the middle open/close times fairly accurately. I for one rarely find myself shooting faster than 1/30th second in LF, more likely over a 1/4 second, so this works fine for me.
Cheers,
Thanks for the info, everyone.
If I can get an electronics guru to help me out (and it works) then I will post t here.
Bob,
I was trying to be as exact to the schematics I had as possible. I checked at Radio Shack and they don't have ANY phototransistors, they're all special-order (RSU). I've had a hard time finding any suitable phototransistor.
This project is fairly low in priority, so it doesn't matter that much. When I come by the right parts, I'll buy them.
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