I agree with Rick ... I compared two different testers of this style using shutters that had been professionally tested. Both testers were accurate at slower speeds but both started to go astray at 1/125 and got farther and farther off as the speed increased. I would not trust them above 1/125.
Speeds that most LF photogs care about are the speeds at 1/125th to 1 second. With 4x5 or larger format, speeds faster than this are most often used to exclude the ambient light contribution for daytime flash, for which timing will not be so critical. Someone is sure to chime in with an exception ;-) or start talking about integrated exposures, but for typical situations when stopping down to taking aperture with leaf shutter lenses this can be safely ignored.
However one can quite easily make a very simple shutter tester like this using a much better phototransistor (faster-rise and fall times, a bit more expensive but still under $15). I did and it's sufficiently accurate at these faster speeds. Main issue then becomes setting the right sampling resolution in Audacity, not saturating the sensor by adjusting the light source or aperture, and choosing where to split the rise/fall curves, and interpreting the results.
Does anyone know the accuracy of the Metrolux II 's shutter timer?
I notice there are a couple versions of Audacity. Is a particular version required?
I don't think so.. I just downloaded the latest version from the sourceforge.net Audacity website and used that. It worked fine.Originally Posted by lecarp
FWIW, here are the results of this exercise. Each speed was measured three times, averaged, and then approximated into a fraction. Clearly I need to either spend some $ on CLA's or lay off using higher speeds on most of these.
I guess the old saying is true: Don't bet the farm on shutter speeds above 1/125 with older shutters.
Few years back I purchased a used Universal Counter in the auction site (HP5315A)
for $35 and made a simple interface circuit (it's not that difficult). I use a pocket laser as a light source because it allows me to measure the opening/closing, necessary to get a real speed number.
And of course, depending on the shutter design and the F selected, the effective speed is not a unique number.
My suggestion is not to assume as a fact you shutter is slow based on some dongle you connected to the mic port. That device only will give you an idea all the way to 1/30s the most.
The field is a different story. If after filters correction I still using anything faster that 1/30s for landscape it means I'm using the wrong emulsion/ISO.
I'm curious why you seem to imply that measuring shutter speed using a phototransistor is more accurate with a laser than with a single-point LED light source--in either case you're measuring the length of time between semiconductor turn-on and turn-off by a point light source as seen through a shutter. And in each case you're measuring opening and closing. It's true there is some unknown pulse delay built into the audio chain in a sound card, but that delay is the same for both the start and stop pulses, so the actual time/distance between the pulses (as measured on a video display timeline) still remains the same. Any delay or distortion involved might be a factor in obtaining a reliably consistent turn on/off, but if the light level from the source isn't overdriving the semiconductor (thereby causing major pulse distortion) then the actual time duration between pulses is not difficult to measure.
It's very easy with any good audio editing program to visually measure portions of a second down to at least four decimal places (five is not all that hard, either), more than what's needed here. The limiting factor is mostly related to human difficulties in consistently placing the editing program's timeline cursor on the correct points in the rise and fall "curves" of the light-on/light-off pulses. Because of that, there is an increasing amount of human error introduced at much over 1/250. However, that error only becomes really difficult to manage above 1/500 or so, because that's when the pulse on/off time you're trying to capture is beginning to approach the maximum switching speed of the semiconductor device--in other words, the start pulse and stop pulse get so close together (or at least so close the response of the audio chain becomes a major factor) at very high shutter speeds that they begin to merge, making it very difficult to measure where one stops and the other one starts. The ideal thing to look at and easiest to measure would of course be a perfectly square start & stop pulse, but that's impossible because shutters don't physically open and close instantaneously. That's where "shutter efficiency" factor is important for higher shutter speeds, and also where the aperture used becomes more of a factor.
For simple measurements such as I did, though, I used wide open apertures and ignored efficiency, because it isn't much of a factor at slow and medium speeds. Being able to see on screen the actual opening and closing curve of the shutter's blades is, in my eyes, actually one of the benefits of using the "dongle", as you put it. Hesitating or inconsistent shutter blades are easy to spot, and once you get some practice in consistently placing the cursor on the proper spot on the curve, very consistent and repeatable measurements to four decimal places becomes pretty easy. And four decimal places is a lot better than 1/30 second.
Frequency counters have much the same problem as human eyeballs in interpreting wide pulses, though. Feed a counter a pair of wide pulses with very little time separation between them (ie, a very high shutter speed), and serious errors will result, so pulse shape and repetition rate are important limiting factors, just as they are with a "dongle", a sound card, and the human eye. You have my curiosity going, though, so I think I'll fire up my HP counter and TEK scope and see what I can see.
Shutter testing is an interesting subject, makes me wonder exactly what procedure Nikon and others measure 1/8000 sec and more in some of their shutters. I guess that's where the $5K+ shutter testers come in, as opposed to the $14 deluxe model I used.
The only advantage of the laser is to position the beam in any part of the opening area in the shutter, most common in the center and in the border. The difference divided by two will you a number near to the open / close time.
With the HP Counter ( used as time lapse ) I can set the levels in the comparators (going up and going down) and the only cutoff is the capacitance of the cable entering the counter.
I set the limit for that simple circuit to 1/30s because of the precision. 25% or 1/4 stop is significant for trasparency film. In fact, for those interested in using the phototransistor method, the circuit is redundant. The input in the PC is a pull-up resistor to +5v followed by a highpass capacitor, so all you should need is to connect the phototransistor (or photodiode) directly to the input.
Now, if you suspect sticky blades in the shutter, the Casio ex-fc100 has a mode to record 1000 fps in a very small resolution (and noisy too) but good enough to find any
troubles.
I just went looking for shutter testers, and I found S.K. Grime's Leica shutter tester. This version was not made by Leica, but the concept is so revealing! A drum with slits, running at a constant speed! (slaps forehead)
So of course the question really is, how did they accurately measure speeds before electronic dohickeys were available? Of course, by tripping the shutter against a bright intermittent light source. Like the slit drum.
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