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.
Don
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.
... I think
Andy
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?
Stephen
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.
