I can easily see the image quality being dependent on the pinhole diameter, wave length and selected focal length, but I would still think the focal length is dependent only on the distance between the pinhole and the film plane.
Originally Posted by keithwms
In other words, if you construct a pinhole camera without the ability to move the film plane relative to the pinhole, you will end up with a fixed focal length camera (i.e. a with a fixed angle of view for the image size of the camera.) I do believe you are correct in that for a fixed geometry pinhole camera you would need to adjust the pinhole size dependent on the wavelength of light you wish to emphasize, or else be willing to sacrifice some image quality.