Re: Leaf shutters

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Don, You have been told wrong. If what you say were true, the amount of "vigneting" would vary between f/16 and f/8 with a focal plane shutter! A different condition you might say? Then consider this tripod experiment:

Experiment: Assume a correct exposure is f/5.6 @ 1/100th sec., but instead you shoot three times as a multiple (triple) exposure. All exposures are at 1/100th sec., but the first is at f/16 (1/4 the required light), the second at f/8 (1/2 the required light) the third at f/16 again (1/4 the required light again) for a total correct exposure. We have now simulated the effects of opening and closing of a leaf shutter, we just broke it into 3 segments. Do you expect that "vigneting" due to this type of exposure will be observed? Of course not!

---------------------------------------------------------------
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I don't like them myself. They're pretty bad.
I grieve over them long winter evenings."
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----- Original Message ----- From: "Don Roberts" <droberts@xxxxxxxxxx>


I hate to disagree with so eminent and learned personage, Andy, but it was always my understanding that the design of a leaf shutter guaranteed that the center would receive more light than the edges. Just picture the way it works. It opens from the center to the edges and then reverses the process. The center has to receive more light. The difference in the amount is insignificant though for a properly functioning shutter. There is less difference at slow shutter speeds than high speeds. The blades moved at a constant rate; if they were able to move faster from the center and slow down toward the edges, the disparity could be resolved. 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. Or so I have been told many times in my early days in photography.
Somebody correct me if I am wrong.  Politely, please.

ADavidhazy wrote:
Stephen,

The center of a photograph is not any more exposed than the edges due to the left shutter. Lens design has a lot to do with the degree to which the non uniformity of exposure from edge to edge or corner to corner of a photograph is apparent. Something called the "cosine to the 4th power" is a factor at work. It has to do with the angle at which light rays arrive at the lens and the image surface ... and the distance they have
to travel to get to the image plane.

Some really wide angle cameras had a whirling fan installed in front of the lens to physically dodge the image forming rays allowing more to go to the edges than the center of the image. Others used a greyscale mask to try to accomplish the same thing. Some new lenses have included in their design a function that makes the aperture appear to get larger to light rays arriving at an angle than those that arrive more from directly
in front of the lens.

Stephen Ylvisaker wrote:

When shooting using a camera with a leaf shutter, do any of you have a way to counteract the leaf shutter effect? I mean, it's certainly not what I would call vignetting, but it is very apparent the center of the picture is the brightest point. And, I know it could be taken care of in the "printing" process by burning the center down a little bit. But, is there an "in-camera" method to counteract the effect?


greyfell@xxxxxxxxxxx
"...decide...whether or not the goal is worth the risks involved. If it is, stop worrying....", and "Worry retards reaction and makes clear-cut decisions impossible." - Amelia Earhart, aviatrix.


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