I seem to remember reading several years ago, that shutters only had to be 40% within the marked speed to meet with the required standard, has anyone any idea if this is still the case,or what the current standard is ?
Somewhere I have a Synchro-Compur service manual that has a chart for shutter speed accuracy. As I recall it ranges from ---- ahh let me go and find it ----. Ok, from 1/125'th and slower, +-15%. 1/250'th and above +-20%. That's as per the manual. Whether this is the current "standard" or not I don't know.
Originally Posted by Bentley Boyd
Mr. Bartley's response, quoting factory literature, is of course completely accurate. However, this manufacturing tolerance is for new shutters.
My experience (rather than quotable documentation) is that electronic shutters (as in new 35mm cameras) are right on the money.
Mechanical leaf shutters, as in view cameras and Hasselblads, are activated by more than one set of springs for various speeds. It is not possible to time the length of a one second exposure and translate that error to the 1/125th second setting.
These shutters are almost never too fast. With time, fridgid environment and prolonged inactivity, they tend to slow down. One of my duties as a studio manager in Hollywood was to get out all the lenses every Friday afternoon and repeatedly work their shutters.
If you can afford it, having your shutters serviced and calibrated by a professional is a good idea. A cheaper solution might be a simple digital shutter speed tester from Calumet.
If you have only one shutter, base your film exposure tests upon whatever it is giving you. It doesn't really matter what the actual speed is, as long as it is consistent each time.
Just remember that buying another lens will require more film testing.
Cloth, metal, mechanical, electronic, blade, old or new , expensive or cheap ? All quite different.
A good modern electronic shutter like in a F100 should not have more than max 1/4 stop at the fastest times ( 1/4000) and the very slow times,if at all.
Good mechanical shutters usually have a bit more tolerance, and are (as I was said once) mostly calibrated to work at 1/125sec absolutely correct.
Old or cheap shutters can have considerable tolerances and for slide film this issue can play a role indeed. One should test it with bracketing tobe sure.
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Old leaf shutters will tend to be on the slow side, but not always at the top speed where there might be an extra heavy spring engaged just for that setting. I have one that seems to be about 1/3 stop too fast at 1/400 sec., based on exposures.
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I second the Calumet shutter tester; easy to use, just takes a minute or two per lens, and also will show you the spread of what your shutter fires at, or the precision, which is important. My experience is that many older shutters, like ILEX tend to be off in terms of accuracy, but if you know how much, you can make a simple adjustment.
I just got a Dagor lens in an ILEX, and did a quick test; the 1/50 speed was actually 1/30, and the 1/25 was actually consistently 1/15 second. Very important to know for portraits. For landscapes I tend to use the B setting, as the slower speeds (1 sec.) of older lenses are usually not precise.
I tested about 8 older LF shutters last month on a digital storage scope and found they ran from 15% to 50% (without service)
Judging by my experience with all kinds of old and not-so-old cameras, usually the average mechanical shutter works well within in 1/3 - 1/2 stop from the expected value. I measured it on tons of cameras with a digital storage meter (a Soviet one, made on radio tubes ). The error is usually non-systematic (e.g. 1/30 can be slower, say, 1/25 - but 1/125 is something like 1/150), especially in older leaf shutters. It all can be cured during a good CLA - in leaf shutters by filing down or delicate squeezing out the worn profile on a speed-setting ring. As far as I can remember, 1/3 of stop was a factory tolerance in both GDR and USSR, but the new specimens were usually close to set values. It shouldn't bother anyone, though - except ZS people, maybe.
Cheers from Moscow,
What of aperture accuracy? I can imagine that those
very small openings are not at all accurate; easily off by
as much as some shutters. Any test for that? Dan
Isn't it wonderful that the emulsions we use have almost enough latitude?