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From: smh@mhuxl.UUCP (henning)
Newsgroups: net.rec.photo
Subject: Re: Shutter Speeds for Focal-Plane & Leaf Shutters
Message-ID: <453@mhuxl.UUCP>
Date: Sat, 11-Jan-86 15:10:10 EST
Article-I.D.: mhuxl.453
Posted: Sat Jan 11 15:10:10 1986
Date-Received: Sun, 12-Jan-86 00:37:28 EST
References: <24800003@gypsy.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 32

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From the keys of Steve Henning, AT&T Bell Labs, Reading, PA mhuxl!smh

> What about cameras with leaf-type shutters, as opposed to focal-plane?
> Since the total time that the shutter is open is considerably less,
> it would seem that you could get away with a slower speed and have 
> less vibration than with a focal-plane shutter.
> 
> Another suggestion: if your focal-plane shutter moves vertically 
> across the film (as in my Nikkormat), you can probably use 1/125 and
> get stable results.  At least, you can most likely use one stop 
> slower speed than with an equivalent horizontal moving shutter.
> 
> A final question: With a leaf shutter, why isn't the center of the 
> negative overexposed, and the edges underexposed, since the shutter
> leaves the center of the negative open for a longer time than the 
> edges?

All three statements are wrong.  1) A grain of film, or any feature on the
film receives light from the lens for the same time with a focal-plane
shutter as with a leaf shutter set at the same speed.  The difference is
that all grains receive the light at the same time with a leaf shutter, but
with a focal-plane shutter the film on one edge receives its light about
1/80th of a second before the other edge of the film.
2) Again, a vertical shutter exposes the light from the lens to the film
for the same length of time as a horizontal shutter set at the same speed
so the blur is the same for the same shutter speed.
3) The leaf shutter is placed at a point where the rays of light do not
correspond to their position in a picture.  That happens to be the place
where your focal-plane-shutter lenses have their aperture.  Otherwise
as you closed down your lens, the outside of your picture would disappear
rather than dimming the entire picture.