Speed Graphic Shutter Checking?

[Jim Galli]

I think the OP is on the right wavelength (at least to my limited intelligence) with the idea of measuring the exact time in a straight line that it takes for the chosen width opening in the curtain to travel past that line.

With a movie camera if I have a 15 degree opening traveling at 250 revolutions per second (I used high speed movie cameras to gather scientific test information) I divide 15 into 360 = 24 times 250 (frames per second) = 6000 and the inverse is my speed. 1/6000th second exposure.

You'd be doing the same thing with a laser measuring the time it takes the slit to pass by. It works the same as the adjustable angle in a rotating shutter.

[jp]

As an experiment today, I took five minutes to use an LED and oscilloscope as discussed earlier. With the lens wide open and an LED torch pointing through the lens, the signal was about 200mV, but clearly showed that the 1/250th second was a shade slow at 4.2ms (should have been 4.0).

So this is a viable option. Note that (also as discussed) if the lens is stopped down not only will the signal get smaller by 50% per stop (though a brighter light will help) but the shutter will get faster. I didn't measure the rise- and fall-time of the signal - it was a very quick test - but it was under a hundred microseconds for each. The LED should have a response time in microseconds or faster.

Neil

If you are using a red LED, it probably has a quick response time as it is built very simple. if you are using a white LED, it probably has phosphors that hurt response time.

[Dan Fromm]

Note that (also as discussed) if the lens is stopped down not only will the signal get smaller by 50% per stop (though a brighter light will help) but the shutter will get faster.

Neil, pardon my denseness, but you've lost me again. Twice, in fact.

I can't see the earlier discussion you referenced. Please direct me to it.

And I can't see how changing the lens' aperture will affect a curtain shutter's slit width and traverse speed. I've always thought that these two controlled exposure time and are completely disconnected from the lens.

[HT Finley]

I have though about leaf shutters too. But I believe they're concerned the amount of time that the shutter is resting at full open with the open and closure time itself largely neglected. But truth is, that the shutter is actually like the diaphragm, except t goes through the range of f/infinity to f/1 billion, ten thousanth, f/256, 128,16, and such until it reached the actual f stop the diaphragm is. Then reverses back to infinity. In other words, measuring to the inward sides of the rise and fall times, and ignoring the actual rise and fall times. Both shutters are imperfect. Consider the heavy Graphic FP shutter (compared to a 35). The top of the frame opening is bound to be overexposed compared to the bottom of the frame, because it has no inertia at the top. But I'm not quite as picky as this post. I just want my shutter within Ektachrome/ Kodachrome requirements. 1/4 stop, maybe? That shouldn't be too much to ask. First a known linearity of the test method is needed. I'm sure it would be nice to have a scope with a remembered waveform. But I figure most of us guys are liable to be tinkering with cutting up mice and using sound programs and other such ideas.

[Jim Graves]

It takes longer to read this ... and the archived threads ... than it does to put a roll back on the camera and shoot & develop the film ....... which is what you are going to have to do anyway.

I have tried probably 6-7 different versions of shutter timers (including the Calumet) and found them acceptably accurate at low speeds (<1/125 sec) ... but lacking at higher speeds. And, in the end, I still had to run film through the camera to see what I had. Now the timers just sit in the drawer when I get a new shutter.

[Dan Fromm]

It takes longer to read this ... and the archived threads ... than it does to put a roll back on the camera and shoot & develop the film ....... which is what you are going to have to do anyway.

I have tried probably 6-7 different versions of shutter timers (including the Calumet) and found them acceptably accurate at low speeds (<1/125 sec) ... but lacking at higher speeds. And, in the end, I still had to run film through the camera to see what I had. Now the timers just sit in the drawer when I get a new shutter.

Jim, I agree completely on the first point.

Y'r second point puzzles me. Why do you think that erratic measured shutter speeds, if that's what your problem has been, are due to an erratic shutter timer instead of an erratic shutter or variations in your measurement procedure?

If your concern is that leaf shutters that the timer says run slow at high speeds still give perfectly good exposure, think about shutter efficiency. That is, because leaf shutters are only partially open for most of the open-close cycle at high speeds, they pass more light that one would expect from the time between fully open and fully shut.

To get back on topic, which is how best to test a Speed Graphic's focal plane shutter, these beasts are much more efficient than leaf shutters at high speeds.

Remember, shutter speed testers don't measure how much light the shutter passes. They measure the time from just starting to open to fully closed.

Finley, you wrote:

I just want my shutter within Ektachrome/ Kodachrome requirements. 1/4 stop, maybe?

This is idiotic, and not because you mentioned Kodachrome even though he last Kodachrome line shut down 12/31/2011 and K'chrome hasn't been offered for LF for more than half a century.

Your wish is idiotic because you want your shutter to be perfect. Shutters aren't perfect, but they can be consistent. That's what you need. That's what the rest of us who test instead of making silly noises check for and rely on.

[Tin Can]

And just for chuckles, tomorrow I hope to test the flapper on my Graflex RB Series B 2x3. This thing is very, very clean. I never shot it and found it today in the shed.

It has a well done BiPost flash sync installed and a small Heiland flash bracket. But no Heiland.

I don't wind these up to 1/1000 as I have had 3 flap away into display items. 2X3 versions seem very delicate and the most difficult to fix.

I know these were designed to use very long duration flash bulbs so the bulb would provide light during the complete slit movement across the emulsion.

I have flash bulbs, but none are long burn. I am going to try slow shutter speeds, big slit with Studio Strobes or LED.

This won't tell me anything about shutter speed, but it may show something about sync issues.

Suggestions Dan? Anyone?

[Jim Galli]

Dan, sometimes people engage a problem for the joy of solving it. I recall one silly person who was devising rediculous solutions for crazy long lenses on a 2X3 format camera? Remember him?

[Tin Can]

It's gets worse, I have read and forgotten everything I could find on Dan's 2X3 adventures.

[barnacle]

Neil, pardon my denseness, but you've lost me again. Twice, in fact.

I can't see the earlier discussion you referenced. Please direct me to it.

And I can't see how changing the lens' aperture will affect a curtain shutter's slit width and traverse speed. I've always thought that these two controlled exposure time and are completely disconnected from the lens.

Ack. Posting while half asleep - I conflated what I posted earlier in the thread and what I intended to/thought I had posted... I fear I have also lost myself

Sorry about that.

You are quite correct: for a moving slit shutter, the aperture of the lens makes no difference to the exposure time. The position of the sensor *may* make a difference depending on the acceleration profile of the shutter blind.

What I did yesterday was just a quick proof-of-concept using a single green LED as the sensor and a lens shutter. In this case a wider aperture *may* have a slightly different duration than a smaller (there's a bigger hole to expose) but the position of the sensor should make no difference. The aperture will change the amplitude of the detected signal.

As someone else pointed out, a WHITE led is unlikely to work in this approach: they are usually UV emitters surrounded by phosphors selected to glow white. I chose green as I had a bag of them on my desk and I would have had to walk into the store-room to find the bag of red LEDs - but I should do a test to see which has the higher output. I also have some two-terminal phototransistors somewhere around the place, but those require a suitable resistor and power supply to operated - though they should be significantly more sensitive.

TL;DR: Using a cheap green LED and a light source I was able to demonstrate a cheap usable timing measurement system.

Neil