1 nov 2007 kl. 19.49 skrev Don Roberts:
...Just picture the way it works. It opens from the center to the edges and then reverses the process.
Agreed.
The center has to receive more light.
Not necessarily. In most shuttered lenses, the shutter is placed in between the lens elements, in a position where the light is totally unfocussed, and so would the image of the shutter blades on the film plane. So, for any moment of the shutter´s cycle, the star shaped opening would be so unsharp on the film that it would show up as a uniform shade of grey, and so the illumination would in fact be even across the field (as far as the shutter influences it).
Another effect that might be mixed up with this is the interaction between a leaf shutter and the iris diaphragm placed close to it inside the lens. For small f/stops, much of the opening and closing of the shutter is "cut off", resulting in a shorter effective shutter time than a fully open lens would give at the same setting. I seem to recall that S:t Ansel did mention this somewhere... and that it is called "shutter effficiency".
... It was virtually impossible to make a leaf shutter that would function at high speeds which was a reason for the development of the focal plane shutter.
Certainly; to complete their work at very short time settings, the shutter leaves would have to move at an extremely high speed, then reverse their direction and return at a similar speed. Especially for larger or faster lenses (where the shutter diameter would be larger), this would place impossibly high stress on the material in the leaves. But this is unrelated to the effects we discuss here.
Somebody correct me if I am wrong. Politely, please.
Well, I do hope you take it that way; no intent of being impolite.... :-)
Per Öfverbeck http://ofverbeck.se "In a world without walls or fences, who needs Windows or Gates?"
