| Author | Message | ||
     rick oleson Rating: N/A |
Hi Charlie: The f/stops will be consistent, but at the highest speed or two the speed will not be the same for all f/stops. Due to the travel time of the blades, in order to get (say, for instance) the equivalent of 1/500 second worth of light to the film at full aperture, the total time from when the center begins to open until it's completely closed again might be, say, 1/250 second, with very little light coming through at the beginning and end of the time and only having a really full open condition for that instant as the blades reach their farthest open point and begin to close again. When the lens is wide open, this varying light intensity can be calculated out and adjusted to give the equivalent of a perfect 1/500. But, if the lens was stopped down to f/16, the full area of that small f/16 opening has been exposed very early in the process, and most of the time the blades spend opening and reclosing is lost because they are hidden behind the aperture blades. In this case, the shutter has been fully open at f/16 for the full 1/250 second or very close to it. At intermediate aperture settings, you get a compromise between these two extremes, so that the same, perfectly adjusted shutter gives a different effective speed for each aperture chosen. There is no way to adjust this out, it's just a fact of life with a leaf shutter that there will be roughly a one stop difference in shutter speed from the largest to the smallest aperture at the fastest speed setting. At slower speeds this effect goes away, as the time spent with the blades stopped in the full open position far exceeds the time spent in a continuously changing condition... the slower the speed relative to the shutter's fastest speed, the more nearly ideal the speeds become. : ) = |