Re: pinhole photography/ calculating focal length

Colyn Goodson (
Wed, 09 Jul 1997 03:26:21 -0700

Bozhidar Dimitrov wrote:
> Adam ( wrote:
> : >"Geoffrey V. Brown" <> writes: > 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.
> : >I do this often with a Pentax Spotmatic with a body cap with a pinhole in it.
> : >It is about equal to a 45mm lens, and I would guess that it will be about
> : >the same on a T-90.
> It will depend on the camera register (distance between lens mount and
> film). I thought about this some more last night, and I think that a
> pinhole has no specific focal length. One definition of f is a distant
> image is rendered the same size as through a pinhole f mm away from the
> film. SO moving the pinhole back and forth (while adjusting the size of
> the opening [for best results]) is like a zoom lens with an infinite range.
> I think...
> Boz Dimitrov
>>The only way to change focal length is to move the pinhole closer to or farther away from the film plane......