View Full Version : leaf type shutters

doreen leo
14-Sep-2001, 17:10
Why do many leaf type shutters only have speeds up to 1/125? Why/why not? Does the speed of a leaf type shutter change if the aperture or f/# changes? Why /why not? Does ambient temperature have anything to do with shutter speeds? Why/why not?

Bob Salomon
14-Sep-2001, 17:41
Large leaf shutter and self-cocking shutters have lower speeds. Usually due to the force needed to reach higher speeds at the size of the maximum shutter opening is not possible.

0 and 1 shutters are 1/400 or 1/500 so they do reach faster speeds.

Some leaf shutters like the Rollei Linear motor PQS can reach 1/1000 at all apertures while the high speed shutters on some other cameras like the Graphic and the old Minolta 35mm rangefinder could hit 1/1000 at small apertures only.

Dave Schneidr
14-Sep-2001, 17:44
I'm sure there are more qualified respondents on this list, but let me give you a layman's answer.

Imagine that any individual leaf of the shutter travels half the diameter of the opening while the shutter opens, then stops, and travals half the diameter again to close. I large shutters like a number 3, that is quite a distance to travel at such speeds. It is simply not possible to create a mechanical spring device that will move that much mass at the required speed to be reliable and accurate.

The other thing to consider is that the shutter is partially open during it's travel time. That is why you see adjustment factors for large leaf shutters when using the lens at wide apertures. You could imagine 1/125 second exposure at f 5.6 to actually be a series of 1/2000 second exposures at f90, f64, etc, until you reach wide open and then the same series of exposures as the shutter closes.

As a final point, how often do you need shutter speeds faster than 1/125 second when using your Copal 3 shutter?

Charlie Stracl
14-Sep-2001, 19:41
1. Bigger shutters have slower speeds; the mechanics of moving larger leafs with greater mass is part of the reason; another factor, perhaps more imporant, is bigger shutters are often used on longer focal length lenses, where smaller stops are usually used to give reasonable depth of field, so faster shutter speeds aren't of much use.

2. The speed doesn't change as the aperture is changed, but the efficiency does. That is, the shutter is opened to full f-stop aperature size for a bigger percentage of the time.

3. Ambient temperature does have an effect on the shuter speed. If lubricated, colder temperatures can slow the shutter, and higher speeds can speed it, as the lubricant moves less or more freely; tolerances change with temperature, which can vary friction even in an unlubricated shutter, which can change speed; I suspect, but do not know for a fact, that the spring constant of the springs in the shutter can change with temperature, thus changing the spring force, and effecting the shutter speed.

So with all these potential problems, why use them?

They are generally very reliable, and offer "good enough" accuracy for most photography.

Flash sync is available at all speeds.

They are practical for LF work, where focal plane shutters are less practical.

They are much quieter than focal plane shutters.

Jim Galli
15-Sep-2001, 00:37
People that have the means to test almost ALWAYS find that those higher advertised speeds are optimistic.......sort of like horsepower about 1969. Ford had 271, so Chevy had to have 285 etc. The answer to your second question as regards shutters in common use in view cameras is NO. The blades fully open to their limit of travel each time the shutter is fired whether you have a tiny aperture or not. J

Michael S. Briggs
15-Sep-2001, 12:25
People more familar with 35 mm cameras are sometimes surprised by the slower fastest speed of leaf shutters. The shutters of 35 mm cameras achieve the fastest speeds by exposing the film through a slit: the closing blades of the shutter start to move before the opening blades have finshed their motion. If you look at the fastest focal plane shutter speed at which the shutter blades are fully open for an instant, which is the flash synchronization speed, and compare that with the fastest speed for which a leaf shutter is fully open, which is the fastest speed of the leaf shutter, than the two speeds are much closer. For example, on the low end of the range, the flash synch speed of a Leica M6 is only 1/50 of a second, while on the high end of the range a Nikon FM2n has a synch speed of 1/250. This comparison shows that the mechanics of accelerating the shutter blades aren't really that different between the two technologies.