Thanks for everyone's input. I will agree that two of the three Supermatics that I've tested seem to be pretty consistent, although slow. A Supermatic I completely rebuilt on a Medalist II about five years ago, was dead on consistent after the rebuild for the four years that I owned it afterwards. Have not rebuilt the Graphic Supermatics but maybe that is the direction I will go and just keep it with the "speed card" and adjust the aperture accordingly.
Best,
-Tim
Over the years I've had really good luck at finding "trashed" optics in excellent COPAL 3 and ILEX No. 5 shutters for just a few hundred dollars each on auction sites. People seem to overlook the shutters and value their items based on the glass. Also have found both these shutters in NOS condition FS from camera dealers in NYC. I think that it's the younger employees wanting to get film related items off their back shelves or just freeing up space in their back stock rooms.
I'm wondering about the origin of the "30% accuracy" that's mentioned above? Was this the "accuracy" claimed by manufacturers (i.e. Copal) for new shutters, or is it the accuracy typically claimed by repair centers when they adjust the speeds of a used shutter. Not sure.
With the testing that I've done on many shutters, in the large majority of cases, I find that individual speeds of a shutter are consistent to within 1/5th stop. Not infrequently, they are consistent to within 1/10th stop, and infrequently I find that a shutter speed is consistent to within 1/3rd stop. If a shutter speed's inconsistency is greater than 1/3rd stop, I designate the speed setting to be unreliable. And these numbers are conservative, in that they represent the range (max subtract min) of several measurements. So, the typical distance of these numbers from a shutter setting's mean speed is less. Suffice to say that used shutters are highly reliable, if one tests for and knows a given shutter speed's mean. Whether or not a given shutter setting's mean speed is the same as it's nominal (marked) speed is a much different matter. Often not.
Consequently, I determine the mean speed of each setting of all my shutters, and I list the difference in stops of these mean speeds from the shutter speed's nominal that's listed on the shutter speed dial. This enables me to make an aperture correction (in stops of course) for speed inaccuracy when I make an exposure. I put all these aperture corrections for all my shutters on a 4x6" card that I carry with my kit. (See photo.)
In summary, shutter speeds are frequently inaccurate, but they are highly consistent. Knowing and adjusting for shutter speed inaccuracy enables one to obtain very accurate exposures on the negative.
Industry standard.Originally Posted by neil poulsen
Following up on Dan's suggestion, I checked to see whether shutter efficiency and angle off axis had any impact upon apparent tested shutter speeds. These were sampling-type checks, not the exhaustive and repeated 3X testing of every lens at every marked shutter speed done several days ago and reported earlier.
I tested lenses mounted on a Seiko 0, a Copal 0, a Copal 1, a Copal 3, an Ilex Acme 3, an Ilex Acme 4, a Compur 0, and a 100+ year old Compound shutter,
I first checked my Calumet shutter speed /tester. As Dan notes, it has a sharp luminance cutoff but if you exceed the luminance cutoff, then it works repeatedly at all brighter luminance values. I first did some calibrating tests and determined that with my test setup of a bright halogen lamp the Calumet would record the same consistently repeatable shutter speeds when tested wide-open at f/5.6, and then at f/8, f/11, f/16, and f/22.
I then tested the various lenses/shutters at normal LF shooting apertures of f/22 and f/16 and at marked shutter speeds of 1/15 for modern shutters and 1/25 for older ones. These seem consistent with typical LF shooting practice. Slower shutter speeds should show even less variation due to shutter efficiency effect.
All shutters except a 100 year old Compound shutter reported the same consistent speed down to f/22 regardless of aperture. These reported stopped-down speeds were very close to the prior wide-open, on-axis test results of a few days ago. The very old Compound would only activate the Calumet shutter speed tester down to f/16, but why that might be is a question for another day.
Result: There were no discernible differences in the reported shutter speeds when tested at the various apertures at 1/15 and/or 1/25. My tentative conclusion is that shutter efficiency is not a concern at typical small LF shooting apertures and relatively slow shutter speeds. It might be more of a problem with leaf shutters at wide apertures and fast shutter speeds typical of smaller formats.
I also checked to see whether there was any apparent speed difference with the shutter speed tester located at about a 15 degree angle off-axis. I saw only an occasional, minor (i.e., less than 1/4 EV) difference with the sensor located off-axis at small f/16 and f/22 shooting apertures, nothing that would require altering calculated exposure. These may be artifacts in any event. Note, this doesn't test for Cos 4 exposure loss off-axis, but only the apparent shutter speed at that off-axis location.
Joe, thanks for the report.
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