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Re: [ATM] 8" Astrograph
> perfect to the Airy Disk situaltion (the grain
> of the film is a lot larger than the Airy Disk for any decent sized
> scope)
> means that SA can be used to an advantage to more fully illuminate >
the grain of the film.
> Bob May
Agreed, in a general sense, but I could add to this that
grain size depends on the film. Lately I have been using
Ilford PanF (B&W, ISO 50). This film is just plain
remarkable! Those who have not yet tried it should do so.
I have some poster-sized blowups from 35 mm PanF that
look flawless. I do not think the grain can be more than
a couple microns, tops. Polaroid Polagraph autodeveloped
film is below 5 microns. These films are both still
available, the latter being a bit of a challenge to find,
admittedly. The "Telescope Optics" book sets a criteria
for a spot size for the wavelength of interest to 25
microns for a photographic system, but I would tend to
drop that down to 10 microns or less these days.
If one then considers the recent lines of "point-and-
shoot" CCD cameras that are 5 MP on a 1/3" surface,
the numbers work out similar, actually: a pixel works
out to be about 3.7 microns. I think the Nikon D70
active surface even works out to be about the size of a
35 mm frame.
Dominic
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