Prosch Duplex brass lens timing issue

[Theerikjohnson]

I recently inherited a lovely Rochester Optical Co. Elite 5x8 with a Prosch Duplex. I've tried to check the shutter times using a couple of different methods: the "Arduino shutter speed tester (http://arduino.cc/forum/index.php/topic,8110.0.html) and a sound card method using the IR emitter and collector from the arduino technique. Both are indicating that the shutter at each speed opens twice, or has a bounce. The total time that it is open on it fastest setting is about 1/30th of a second. The diagram in audacity shows two approxamitely equal peaks.

Has anyone experienced bounce with these shutters? Or am I maybe using it wrong?

Thanks you looking.

[Steven Tribe]

Welcome!

I suppose it couldn't be because the two "traces" indicate opening and closing - and the time open is the distance between the two peaks?

[Theerikjohnson]

Thanks for the thought. What I'm describing as peaks are really two plateaus with a valley between them. The shutter is all the way open at the start of the plateau and closes at the end of it, then a valley, then another plateau. This is in line with the IR collector only recieving a signal when the shutter is open.

Any other ideas? Has anyone taken one of these apart?
And thanks for the welcome.

[Jody_S]

Thanks for the thought. What I'm describing as peaks are really two plateaus with a valley between them. The shutter is all the way open at the start of the plateau and closes at the end of it, then a valley, then another plateau. This is in line with the IR collector only recieving a signal when the shutter is open.

Any other ideas? Has anyone taken one of these apart?
And thanks for the welcome.

Can you place your sensor off-center in the shutter when testing? If there is indeed a bounce, and it's not visible to the naked eye, it is perhaps just the center of the opening that springs open for an instant on the higher speed settings. Or, set the shutter on a lower speed setting and measure again. If the bounce remains and shows a similar time, they you know what it is.

I've patched up a dozen or so shutters from that era, none to date have done this for me, but I have yet to build a shutter speed tester. I know how to do it, I just don't particularly care to know to the millisecond how my shutters are behaving. But I have been looking for an excuse to buy an Arduino board. I started out my working life as a programmer on some similar hardware, of course it cost thousands per board at the time.

[Theerikjohnson]

Another good thought. I did try the sensor of center to the shutter for most of the tests, but I'm not sure the it would make much of difference. A glance at patent diagrams on the old google show that the shutter is just two leafs that open and close like a my drapes. It's not an iris where it would open at the center first. Not sure if that's what you mean?

I only have four choices for shutter speeds with the spring selector and they are all pretty close anyways. The two peaks are about equal size. And for the second to be a bounce it makes sense that the second peak would be a bit smaller and consistent with all speeds, as you suggest, Jody. I'll keep thinking on this.

Jody, you should get an arduino just for the fun of it. I've had a blast with many projects and I'm just self-taught. The shutter speed tester cost me $2 for the emitter and collector, as I already had the arduino. So much fun.

[premortho]

I bought a Probst shutter off the bay a couple of years ago. A Probst Triplex. I bought it to see how it worked. It dragged real badly. I cleaned it as much as I could without total disassembly...still dragged. It was stuck open. I decided to take it apart to clean it better, and as I broke the case screws loose, bingo, it shut. I then cycled it through it's speeds and it worked fine.

[CCHarrison]

A March 28, 1891 issue of Anthony's Photogrpahic Bulletin mentions issues of shutter bounce with the Duplex. See image

Dan

91846

[Steven Tribe]

Incredible!
There are no new problems.
How on earth did he measure that accurately in 1891 - some kind of revolving disc?

[CCHarrison]

Steven, you can check out the testing here http://books.google.com/books?id=SpgPAQAAIAAJ&pg=PA175&dq=prosch+rapid+shutter&hl=en&sa=X&ei=mNpNUZGxAefi4AO48YD4Cw&ved=0CDwQ6AEwAA#v=onepage&q=blake&f=false starts at page 144..

Best
Dan

[Steven Tribe]

Photographing falling silver balls in sunlight and measuring the "track" lengths on the plate - well I never!
The balls have to reach terminal velocity.

[Jody_S]

Photographing falling silver balls in sunlight and measuring the "track" lengths on the plate - well I never!
The balls have to reach terminal velocity.

It's a very simple physics problem to do this if you know the height from which it's dropped, in fact it would work better dropped just above the lens because the classic acceleration formula doesn't account for friction.

[Theerikjohnson]

Thanks all. Good info. I knew I came to the right place.