| Author | Message | ||
     Tony Duell Rating: N/A |
If you consider a 'perfect' leaf shutter, then the light-time curve at the film would be a rectangular pulse. It would open instantaneously, and close instantaneously. A real shutter will have a light-time curve with sloping edges (maybe not even straight). One possibility would be to measure the total amount of light coming through when you operate the shutter, and then use that to calculate the equivalent time for a perfect shutter. In other words, calculate the integral of the light-time curve, compare that to the area of a rectangle. I think (I am doing this in my head) that if the opening and closing edges are straight, then this is the same as taking the time between the half-intensity points on the opening and closing edges BUT -- and it's a big but -- you'll find that this time varies with the lens aperture. It has to (think about what the shutter actually does). I've yet to find a camera which makes any correction for this. And I am pretty sure that many of the cheaper shutter testers (which are still not that cheap!) just measure the time while 'some' light is hitting the sensor. Since the threshold, and the intensity of ambient light, is not known, this will presumably not be very meaningful at the higher speeds. |