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Electronic shutter testing?

 
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RichS



Joined: 18 Oct 2001
Posts: 1467
Location: South of Rochester, NY

PostPosted: Sat Mar 09, 2002 6:14 am    Post subject: Reply with quote

Okay, I'm back withg some more odd questions
I recently went to Calumet (the web site) looking for something, and there on the front page was an electronic shutter tester for a very good amount. I couldn't resist, and I don't regret it. It has already served me well after only two day's use. But it raises some questions...
After testing all my shutters, I found them all to be slow but not overly erratic. Taking a chance on the first one, I shot some graphite into the works and the shutter came right up to speed. Did the same to the rest of them and they all came up to speed. I'm happy, almost... There seems to be a problem with speeds over 1/100th or so. The shutter does get faster but the tester doesn't. I verified the tester's accuracy on a 35mm electronic shutter up to 1/1000, and they do agree to about 1%. But not on leaf shutters. Not even on the much newer Mamiya C330 shutters which I know perform very well.
The 'manual' that comes with the tester tries to explain "shutter efficiency" with leaf shutters and says that most have a 1 millisecond travel time. That would be a total of 2 ms to open & close (that's 1/500 alone). And that the shutters are rated for a fully open time. In the example for this they explain .004 second when tested at 1/500. .004=1/250, the difference being the travel time. And this would explain the slow time I get when testing 1/400 on my shutters. They clock in between .007 to .004 (not all get to 1/400). Does anyone have actual experience in testing shutters this way and is there any reliable way to test the fast speeds?
The other question is about fast shutters... After lubricating mine, now many are a bit fast at the slow end. Some come in at 1/3 second for a 1 second setting, getting closer as speeds go up. Can this be adusted? Is it worthwhile? Or should I just mark the fast ones and make up for it with arperture (seems more pratical to me?)?
Well, sorry again for the long post but the subject of leaf shutter testing at the higher speeds interested me a bit and I thought someone else might also be interested, and maybe know some answers
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extraparts



Joined: 10 Feb 2002
Posts: 59
Location: texas

PostPosted: Mon Mar 11, 2002 12:03 am    Post subject: Reply with quote

Yes they can be adjusted. Most of my shutters have 3 groups of speeds. aprox 1 sec to 1/25...1/50 to 1/200 and 1/400.

Each group adjusts seperately. The slow speeds have a retarding gear train with a pin that hits the speed ring. You can loosen one end of the gear train so that you can move it closer or farthar from the speed setting ring.

Having said all that, I just made a card for all my shutters that I keep in my camera case with the correction factor for each shutter at each speed.

The faster speeds are always off at small apatures f32 etc because most of the blade movement takes place over the closed part of the blades. However, you seldomn use those small f stops with fast shutter speeds so why worry.

Unless I have a very contrasty scene, I always "overexpose" by one stop anyway with B&W. Color is a different story.

Neal
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RichS



Joined: 18 Oct 2001
Posts: 1467
Location: South of Rochester, NY

PostPosted: Mon Mar 11, 2002 4:39 am    Post subject: Reply with quote

Oddly enough, after looking for another repair book, I found one I had bought a while back for Grafex shutters. The info should be in there? But taking one apart is something I'd really like to stay away from unless I have a true spare
But writing down the actual speed makes a lot of sense to me...
And after actually seeing the speeds of these shutters, I'm suprised anyone could shoot chrome without having them cleaned and adjusted. Before I lubed it, one of the shutters was running around 1/75 top speed (and I think it ran to 1/400?). They're all close enough now, except for measuring the fastest speed thing I mentioned. I'll have to do the whole setup and test shown in the Calumet booklet to measure shutter efficiency and judge how accurate they really are at top speed.
The main problem I have is theoretical I suppose. If you make an exposure at 1/400 and the center is actually open for 1/150 or so, wouldn't the negative be rather unevenly exposed? Or does it actually work more along the diaphram idea by darkening the whole area? Hmmm, that makes sense now that I think of it? Maybe all is as it should be after all?
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