copal shutter with slow speeds at 1/400 and 1/250greenspun.com : LUSENET : Large format photography : One Thread
I'm thinking of buying a used lens in a copal 1 shutter. The lens is pristine and I've got some great pictures with it. I don't usually do this but I tested the shutter with a camlogix sh-t2. The slower speeds are perfect but at 1/250 and 1/400 the shutter is slow by a stop. I don't think it is me or the setup because my other shutters are testing right. I don't think I'm likely to use 1/250 or 1/400 anyway.
My question is : Is this a warning that I might have further problems with the shutter or should I just forget the faster speeds that I never use anyway? I should add that while the lens is not overpriced, it's not a bargain either.
-- jerry brodkey (email@example.com), April 04, 2002
I thought they ALL were slow at those speeds. I'm more surprised to hear that you have a couple that aren't. I wouldn't let that stop me from buying it, although I likely wouldn't be above using that as bargaining leverage to try to make a little better bargain. I'm usually thinking of how to do it with flash if I need high speeds. I'll grab a Nikon or Mamiya to chase trains with.
-- Jim Galli (firstname.lastname@example.org), April 04, 2002.
The shutter speed on leaf shutters is generally calibrated to the time the shutter is fully opened and does not include the time during opening and during closing when the shutter is partially opened. According the documentation that came with my Calumet shutter tester, most #0 and #1 leaf shutters take roughly a millisecond (0.001 secs) for the shutter blades to travel from fully closed to fully opened and the same (0.001 secs) to go from fully opened to fully closed, for a total of 0.002 secs, which happens to be 1/500 second. These times are usually independent of the shutter speed. Therefore, when shooting at 1/250 a second (0.004s), there is an additional 0.002 seconds added to the time adding a 1/2 stop difference in time, assuming the shutter tester reads the duration of the "light" (as the Calumet does). It's even worse at 1/500 second wherein the "tested" time will be double that, i.e., 1/250 second (0.002+0.002). At the slower shutter speeds, this "lag" is relatively smaller and does not significantly affect the measured speed.
-- Steve Baggett (email@example.com), April 05, 2002.
I second what Jim says - I, too, thought that they were all slow at those speeds. I've tested Mamiya RB67 leaf shutters, a Schneider and a Rodenstock in Copal 3 and a Leica 35mm focal plane: the only thing that was spot-on through 90% of the range was the Leica body.
If you know what the lag is (and can remember to apply the necessary compensation!) I wouldn't worry about it overmuch.
-- Neil Miller (firstname.lastname@example.org), April 05, 2002.
I rarely worry about shutter speeds, as long as I know what they are. My primary concern is with consistency. How consistent is the shutter? So long as you know the actual (versus the stated) shutter speed, then you can make adjustments using the aperture. Thereafter, you need only be concerned that the shutter reproduce that same speed repeatably.
I bought a Calumet shutter speed tester, and learned a lot about the performance of my shutters. I understand the effect on efficiency of the time that it takes for the shutter to completely open, and the relationship this has with the measurements I obtain with my tester. But, I rationalize that most of my photographs are taken at smaller apertures, so this dynamic shouldn't have much effect. I think the relevant consideration is how much time it takes for the shutter blades to expand up to aperture.
-- neil poulsen (email@example.com), April 05, 2002.
Thanks for all your answers. I'm not sure that the time it takes for the shutter to open is really significant. If it is about a millisecond TXT already begins to show reciprocity failure at 1/1000 second. Also the shutter not being fully open will probably add some light cutoff acting like a diaphragm.In any case my shutter tester has a bias switch so that it can be set to only record when the shutter is fully or almost fully open. I just tested a brand new copal #1 shutter and it well within a 1/2 stop at 1/400. Again, many thanks, Jerry
-- jerry brodkey (firstname.lastname@example.org), April 05, 2002.