Re: pinhole photography/ calculating focal length

Fernando Martinez (fmg1@mx2.redestb.es)
Fri, 11 Jul 1997 23:13:02 GMT

On Mon, 07 Jul 1997 08:37:44 -0400, "Geoffrey V. Brown"
<geoffb@zerozine.com> wrote:

>Well, I've got some extra film and want to mess around with some stuff
>this weekend.
>I'm thinking about trying some pinhole photos, but doing them with my
>canon T-90 with the lens removed and a plate in its place. I'm
>wondering how if anyone has any suggestions on how to calculate the
>focal length.

Ive done it with a old medium format camera, and had good results.
You can asume that the focal length is the distance between the plate
(where the pinhole is) and the film plane. You can measure it opening
the camera back and puting the shuter speed in B, open the shuter and
measure it.
Then, if you asume, also, that the aperture is the pinhole diameter,
you can calculate the f number for your camera. You cant vary this f
number ( except, of course, varing the pinhole-to-film distance or the
pinhole diameter) so you must calculate the exposure time for it.

Fernando Martinez

fmg1@mx2.redestb.es