Mine isn't a storage scope either. If you have a normal scope, you could turn up the crt persistence knob and it would keep the shutter waveform on the screen long enough for you to measure the pulse (e.g., it took 4+1/2 squares). Adjust the time/division to be appropriate for the shutter speed. Sweep trigger wouldn't be important, but could make it nice and neat for the shutter pulse to start at the beginning of the screen.Originally Posted by rdenney
As do I. They are finicky, and to get a clear reading, the light source must be without any pulse at all, and it must also be just bright enough to reach the trigger threshold on the tester. If it is too bright, the readings will be inconsistent, and even the pulsing of an AC-mains-powered incandescent lamp will trigger it untimely. Of course, one still had to convert the reading of tenths of milliseconds (or whatever it was) into fractions of a second, and still had to calculate the exposure error. I ended up using a battery-powered flashlight placed about two feet in front of the bare shutter under test, and I wrote a spreadsheet to turn the numbers into something more useful. Using it was not completely like hitting the EASY button.
They are also expensive now. For that money, I can get stuff that does just as well, shows me the waveform, and provides good toy value for other hobbies as well. But that is even less like hitting the EASY button.
Rick "obviously not always interested in the easy way" Denney
Hope you can stay out of the dog house with this new equipment coming your way.
More on this subject: I have obtained a DPScope, which is an inexpensive digital oscilloscope that connects to a USB port. It's a funky little kit, not without it's foibles (mostly as a result of its serial/USB converter), but once I made it work, it is good for this application.
The scope will record, as a storage scope, one screen's worth of information, including 200 samples on that screen. The screen is a typical o-scope display, with 20 divisions horizontal and vertical. It is possible to set each division to 0.5 microseconds, resulting in the ability to record an event 1 microsecond long at a sampling rate of 20 million samples/second. The vertical resolution is similar, being able to measure input voltage to 0.5% of scale, with the vertical divisions ranging from 5 millivolts to 1 volt. The bandwith is about 1 MHz, which is fine for this application and for audio measurements.
The circuit that I used is very simple. The positive lead from a AA battery single-cell holder is connected to a 4.7KOhm resistor. That connection is where the positive lead of the scope is connected. The other end of the resistor is connected to the collector of an IR phototransistor, Radio Shack part number 276-145. The negative lead to the scope is also connected at this location. The emitter of the phototransistor is connected to the negative battery terminal, through a switch.
This phototransistor is actually a TIL414, which has a rise time of 8 microseconds and a fall time of 6 microseconds. I wrapped black photo tape around the LED to make a soda straw about 3/4" long.
With the leads connected as above, the voltage measured will be the battery voltage at full light, and zero in dim room light. Full light came from a desk lamp with a 100-watt bulb.
The tester is sensitive enough to measure the 1/400 speed on a Compur 00, without removing the 47mm Super Angulon cells (lens at f/5.6).
I set DPScope to trigger on the rising voltage, with the trigger voltage at about .02 V.
I have attached a screen capture of the scope output for the measurement of the 1/1000 shutter speed on a Speed Graphic 3x4 shutter. Given the fast rise time, the somewhat more leisurely increase in voltage is the time required for the leading and trailing edges of the curtain opening to pass in front of the sensor. The phototransistor may have reached saturation before it was fully exposed. If I measure from the trigger point to the first point at which the voltage starts to drop, even slightly, I get a measurement of 2 milliseconds, or 1/500.
The 1/400 shutter speed on that Compur 00 measured 1/300 using this method. This is exactly what I got using the "sound card shutter tester" I bought from ebay, and plugged into a good E-MU external USB sound card. Thus, I do not believe that the fact that the sound card filters out DC prevents it from making reasonable measurements, even up to the 1/500 shutter speed. I measured speeds of 1/450 for one of my Compur 0 shutters at the marked 1/500 shutter speed using the sound card.
Thus, I do not believe that a sound card will undermine the accuracy of these home-made testers. If there are inaccuracies, they are outside the electronics of the tester.
The only conclusion I can come to is that the size of the curtain opening on the Speed Graphic is based on an assumption of the curtain speed at the full winding load of the spring, which would cause the curtain to move faster than for the next curtain opening. Friction may be preventing this. That's the only way I can explain how a narrower slit for 1/1000 provides nearly the same shutter speed as the more open slit for 1/250.
Rick "figuring only about three of us are interested in this at this level" Denney
So now put some film in it and shoot the same scene at 1/1000 and 1/250 and see if you're right.
Rick; that's super cool!
Three and one-quarter. Interesting! I read your post and then went back to sleep.
I just attach my Nikon D300 to the back of my Graflex via an adapter, points the camera at an even surface, and compare the histograms from the Nikon shutter with the Graflex shutter. Easy, reliable.
Hi,
This is my first post here. Actually, my reason for finding and joining the site is because I have just stripped and rebuilt a Speed graphic. I tested the shutter and found it to be all over the place. I then serviced it as per the original service manual that you can find on the net and reassembled it following the 'just enough spring tension to close the shutter when inverted' calibration procedure.
It works... but I have exactly the same experience that you describe in your original post. Up to about 1/300 s the speed seems to increase as I crank up the tension or use a smaller slit. They don't match the speeds printed on the plate on the camera too well - but no matter.They are quite consistent and I can laminate up a table...
The problem is that after this speed the shutter gets no faster. Speeds with a spring tension of "6" are hardly any faster than "3". The spring certainly feels tighter, the shutter makes more noise, it seems to hit the stops harder...but measures much the same speed.
How do I know my shutter tester is accurate? Hmmm.. it is home built. I mentioned the problem to my 'other half' who (rather mockingly, I thought) said 'I suppose you need to build a tester to test the tester, now'. Well... she was right. I'm right in the middle of testing my tester with the shutter tester tester (!) - but preliminary results seem to indicate that, whilst my shutter tester overestimates the shutter speed by an error margin which increases as the shutter speed increases (about 25% at 1/1000s) - it does work and should certainly be able to distinguish between 1/250s and 1/1000s.
So... looks like the shutter really does go no faster than 1/300 s :-(
Anyway... at least you have a fourth person interested ;-)
You can amend that count to five. I've got to do the same with mine eventually, and I'm riveted by this conversation. So, any of you folks feel like preparing a more in-depth (with PICTURES!) guide to it?
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