----- Original Message ----- From: "Richard M. Koolish" <kool...@bbn.com> To: <pinhole-discussion@p at ???????> Sent: Friday, December 14, 2001 7:42 AM Subject: Re: [pinhole-discussion] Jeff Dilcher's photos - questions
> > What the heck is inverse quadratic diminution? Maybe I shouldn't ask! > > I believe you are seeing vignetting. I it seems more pronounced on > > large format cameras with a short focal length. > > > For a flat film plane, the light from a pinhole falls off as the forth > power of the cosine of the angle from the center of the image. One factor > of cosine squared is due to the increasing distance from pinhole to film > and the other factor of cosine squared is due to the fact that when viewed > from an angle, the round pinhole looks like an increasingly smaller > ellipse. That's why the corners get dark in wide angle pictures. On the > other hand, an oatmeal box or other cylinderical camera corrects for these > factors. It will correct for the first factor, but not the second. I believe Larry Bullis came up with a design to correct for the second one.
