Speed Graphic Focal Plane Shutter

[Barry Kirsten]

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.

Thanks Jack, but I'm puzzled because the types suggested for Q1 are all small signal transistors of the type used in amplifiers and other circuits - I can't see how they can function as light-sensitive devices. I'm obviously missing something here, as it appears from other posts that the circuit works. If anyone can put me straight on this I'd be very happy.

Thanks,

Barry

[Jack Dahlgren]

Thanks Jack, but I'm puzzled because the types suggested for Q1 are all small signal transistors of the type used in amplifiers and other circuits - I can't see how they can function as light-sensitive devices. I'm obviously missing something here, as it appears from other posts that the circuit works. If anyone can put me straight on this I'd be very happy.

Thanks,

Barry

Really? I don't see any mention in the list of what phototransistor is suggested. I think a typical phototransistor should work:
http://parts.digikey.com/1/parts-kws/photo-transistor

And yes, you need a phototransistor or something else to detect the light.

[Barry Kirsten]

Thanks again Jack. Yes, the one you suggested is an NPN phototransistor and probably would do the job.

My confusion arose from the list of suggestions for Q1 given by Steve (see page 6 of this thread) - to quote:

NPN:
2N2222
2N3904
BC548
2N4401
BC238

Thanks for the reassurance that I'm not going mad in my old age.

Baz.

[Leigh]

Ok, here's a few circuits as promised.

Those are some pretty bizarre circuits.

In all three cases the phototransistor is just acting as a switch, not controlling the bipolar in any manner.

- Leigh

[Rider]

When I tested shutter speeds, though, the slower speeds were over half a stop slow and the high speeds weren't.

Might I ask how you test the shutter speed?

[rdenney]

Might I ask how you test the shutter speed?

Please read the whole thread. Many of its 8 pages go into that topic in great detail.

Rick "asked and answered" Denney

[Jay DeFehr]

With all the very impressive electronics expertise demonstrated here, has no one considered replacing the spring driven shutter with an electric motor driven one? Or, put another way, how difficult would it be to build an electronically driven/controlled F/P shutter with capabilities similar to these Graflex units?

I have 3x4 and 2x3 Graflex slrs, but I've never worked on the shutters, or even tested them, except by exposiing film. Very interesting thread!

[rdenney]

With all the very impressive electronics expertise demonstrated here, has no one considered replacing the spring driven shutter with an electric motor driven one? Or, put another way, how difficult would it be to build an electronically driven/controlled F/P shutter with capabilities similar to these Graflex units?

I have 3x4 and 2x3 Graflex slrs, but I've never worked on the shutters, or even tested them, except by exposiing film. Very interesting thread!

The electronics seems more impressive than it actually is. The circuits we designed including very few components that could all be soldered together without any special skill. All the talk resulted in the conclusion that the light source and the interpretation of the graphical output turns out to be more important than the circuit (or the computer software), but there wasn't much complexity in the device.

Now, designing an electric motor to run in place of the spring would be more challenging. And the spring is so freaking simple and reliable that it hardly seems worth the effort.

I had though I'd use my Speed for barrel lenses and the like. But I just ordered a Sinar Copal shutter from KEH, so this experiment may have reached it's logical conclusion for me.

Of course, I'll have to test that Sinar shutter.

Rick "thinking Wally's (do a search) time-readout shutter tester is a good commercial solution that works as well as the Calumet tester" Denney

[Jay DeFehr]

Rick,

You're probably right. I was thinking about a project I've had in mind for some time- an 8x10 SLR, for which there is no ready-made FP shutter, which is about 1/2 the design problem. Another problem is moving a big mirror, but I thought I'd try a beam splitter mirror instead of a moving one, and use a mylar view screen to make up for some of the lost brightness there. I thought I could use a pair of small stepper motors to run the shutter, but maybe a spring mechanism would be simpler, and just as effective, but slow speeds are not the strengths of a FP shutter like the Graflex. Maybe I'll mock something up with foamcore; fixed focus, one shutter speed, and see if I can make it work.

[Rider]

I just ordered a Sinar Copal shutter from KEH,

Can that be installed in a Speed Graphic?