There will also be a diffraction effect because of the difference of path length across the pinhole and the wavelength of light. I can't remember the answer but you have to integrate the light arriving at a point from across the pinhole and it makes a difference as it is circular. I will try to do the integration shortly but if I remember correctly there is a term (theta)/sin(theta) in it somewhere. Chris Web Page http://www.chrisweb.pwp.blueyonder.co.uk/ |> -----Original Message----- |> From: owner-photoforum@listserver.isc.rit.edu |> [mailto:owner-photoforum@listserver.isc.rit.edu]On Behalf Of Chris |> Sent: 22 August 2003 19:53 |> To: List for Photo/Imaging Educators - Professionals - Students |> Subject: RE: Minimizing pinhole image falloff |> |> |> At a guess I would say the fall off was proportional to Sin(Theta) where |> theta is the angle of the ray away from the normal. There is no focal |> length for a pinhole. The brilliance of the image is proportional to the |> area of the pinhole. So the brightness at angle theta from the |> normal will |> be proportional to A.Sin(Theta)/d^2 where d is the distance of |> the element |> from the pinhole. |> |> Don't quote me I'm a beginner! |> |> Chris |> Web Page |> http://www.chrisweb.pwp.blueyonder.co.uk/ |> |> |> -----Original Message----- |> |> From: owner-photoforum@listserver.isc.rit.edu |> |> [mailto:owner-photoforum@listserver.isc.rit.edu]On Behalf Of Gregory |> |> Fraser |> |> Sent: 19 August 2003 16:19 |> |> To: List for Photo/Imaging Educators - Professionals - Students |> |> Subject: Minimizing pinhole image falloff |> |> |> |> |> |> I went to a web site that had a calculator for the image circle |> |> diameter of pinhole setups. I calculated that a focal length of |> |> 3 inches would give me an image circle that would cover 4x5 inch |> |> film. I forget the pinhole diameter. Then I remembered how |> |> drastic the falloff is at the edges of pinhole images so I |> |> thought perhaps by increasing the focal length, I would have |> |> more of the brighter central part of the image and that would |> |> reduce the effects of falloff. 'But wait,' I yelled, 'if this |> |> were the case wouldn't Guy have been able to find a hotel room |> |> long enough to prevent the falloff he experienced in Montreal? |> |> Certainly someone as intimate with pinholes as Guy would know |> |> about that.' |> |> |> |> So, does the light falloff of a pinhole camera image follow an |> |> inverse square rule? Will it always be an issue no matter how |> |> big your shoebox, cigar tube or Quaker Oats box is? |> |> |> |> Greg Fraser |> |> |> |> |> |> |>
