| Author | Message | ||
     Rick_oleson Tinkerer Username: Rick_oleson Post Number: 1075 Registered: 07-2006 Rating: N/A |
In skimming over the above discussion, I see a lot about the shutter but not much about how you know that it is running, for example at 1/220 at the 1/500 setting. How are you testing the shutter? The reason that I ask is that a leaf shutter is never intended to be open for only 1/500 second at the 1/500 second setting. Because of the way the leaves open from the center to the edge and then reverse, in order for the shutter to pass the light equivalent of 1/500 second, the center has to be open much longer than that while the blades are still obstructing most of the outer area of the lens. The outer edge is cleared for only an infinitesimal moment as the blades reverse direction. So if, for example, you are testing with a digital shutter tester with the sensor in the center of the lens, 1/220 second might actually be perfectly in spec for the 1/500 speed. At slower speeds this still happens but it is an unmeasurably small effect in relation to the longer time that the blades are held fully open. Another effect of this behavior is that the effective shutter speed at the fast end varies as a function of aperture selected: at f/3.5 you do get an accurate 1/500 equivalent, but at f/22 the entire working aperture is exposed for the whole 1/220. |