Rob Studdert wrote:
> On 5 Jan 2001, at 18:27, Shel Belinkoff wrote:
>
> > Lewis Kemper, in an article in the current issue of Camera
> > Arts magazine, states that when bracketing for critical use,
> > such as registering different layers with different exposures
> > in photo editing software, one should bracket by changing the
> > shutter speed because if you varied the aperture the image
> > sizes would vary slightly.
>
> Hi Shel,
>
> The only article that I have read which has any kind of remote similarity is
> that of the Leica M TEST REPORTS BY ERWIN PUTS for the Noctilux-M
> 1:1.0/50mm which can be found on his web site at http://www.imx.nl
> The paper refers to focus shift but not to a change in image size.
>
> Cheers,
>
> Rob Studdert
On a microscopic level, I can this happening.
Draw a simple lens () () to represent the glass, a triple line to represent the film
emulsion and base | | | , and place
lines representing the diaphragm between the lens elements. Ray tracing from a point
well off center in front of the lens,
and representing the lines entering the lens and converging on a point near the edge
of the film, you will see that at
differing apertures the light rays from the lens that pass near the edge of the
diaphragm hit the film at different angles
with different apertures, increasing as you near the edge of the film. This would
cause a progressively larger image as a
wider area of silver particles was exposed as the aperture decreased in diameter.
We're talking microns or less here.
Not noticeable in any normal image viewing or manipulation, but when you scan several
negatives or slides and try to
overlay them on the computer, you will find a one or two pixel "fringe" between images
otherwise in perfect registration
at the center.
This is mind work, not real life experimentation, so thinking about the process from
start to finish may not represent an
actual experiment. Especially given any latitude in film flatness in camera or
scanner, scanning deviations, etc..
Arguments?
--
JoMac, Imagineering Head
Image * I * Nation, the creative division of RMG Services NW
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