Re: image circle relative to focal length/fstop

----- Original Message -----
From: "Thom Mitchell" <tjmitch@ix.netcom.com>

> Would then a thick material create a smaller circle with the same image
> quality (or not) as a thinner material? These may be simple questions but I
> want to be able to control the size of my image circle, either through
> pinhole size or focal length. It now sounds like material thickness could be
> a 3rd variable to play with, and possibly the most productive. Any other
> advice out there? Thanks for the responses so far. Thom

The 2 variables you have are distance pinhole to film/paper and thickness of the
pinhole material. The distance or focal length will cause a slow light fall
off, as given by an esoteric physical/optical law, sort of. A pinhole made on a
thick material would cause a very fast, almost sudden fall off, due to
vignetting (have the impression this is what you're looking for, but I may be
wrong).

As far as specific examples, calculation would have to be made to find them out
or to find possible rules of thumb, but since the requirement is no math, trial
and errors would have to be made to find a possible relation between thickness
of material and fall-off. The relation between focal length and fall-off was
already answered by Tom in a previous message.

There is a 3rd variable and is the ratio pinhole diameter versus thickness of
material, but let's not go there 'cause it would complicate and augment the
empirical tests.

Guillermo
Received on Tue Mar 26 00:08:07 2002