View Full Version : shutter calibration specs

Don Boyd
26-Feb-2004, 14:28
I have just picked up a recently purchased, used 300mm Nikkor after having it cleaned, lubed and the shutter speeds adjusted. I did not have a chance to talk with the technician but his note says that "all speeds are within factory specs." The speed chart lists the following "marked speeds" and their correlating actual speeds. Where differences exist, do they sound typical and are they indeed, "within factory specs?" (I'm not sure that a table would format correctly on this site, so I will list the Marked speed first, then the actual speed.) Thanks

400/300, 250/215, 125/120, 60/60, 30/40 15/20, 8/10, 4/5, 2/2, 1/1

Joseph Dickerson
26-Feb-2004, 15:29

I'd say those numbers are typical. Mine seem to run very close to what yours are. It is my understanding that you really shouldn't use the top speed on most leaf shutters anyway.

The speeds might be able to be brought closer to the marked speed but it's really not neccesary as long as they are repeatable (read consistant) and you know what they actually are.

To this end I check mine frequently with an inexpensive shutter speed checker to see if anything has slipped noticeably and annually have my repairman do a check for actual speeds.

Steve Baggett
26-Feb-2004, 18:19
Leaf shutters have "rise time" and a "fall time" and an "open time" for each speed, due to the finite mass of the shutter blades. The rise-time and fall-time are essentially constant and represent the time where the shutter is partially opened on its way to full open and when it is partially closed on its way to fully closed, respectively. As you approach the fastest speeds, the rise-time plus the fall-time approaches the actual open-time, and can be as much as 1/500 of a second on a Copal-0. This fraction is immaterial for slower speeds but is a substantial percentage of the faster shutter speeds. For example, my Copal-0 shutters are all within 1/6-fstop of the selected speed until you get to 1/250 and 1/500. The 1/500 settings always record (on my Calumet shutter tester) about 1/250 and the 1/250 settings always record around 1/170. This means that the rise+fall time for the shutter blades is around 1/500 second (2 milliseconds). The Calumet tester uses some kind of photo-detector and so it "starts the clock" as soon as the shutter is part-way open and probably overstates the speed for the faster settings somewhat. According to Stroebel, leaf shutters are supposed to be calibrated so that the marked speeds correspond to the time between the half-open and half-closed positions. I guess the important thing is simply to be within 1/3 f-stop of the marked setting.