Message text written by INTERNET:[email protected] >That's a very useful formula! Not that it would be of practical value, because I'm just using visible light, but does that mean that the pinhole size would change with different wavelenght of light?<
Yes, the pinhole effect is driven by the wavelength of the incident light and of course visible light is a mixture of wavelengths although the effects of such a mixture are not noticeable in a device like this! > I'm not sure where you got 0.047*. Does this figure have something to do with the 550nm wavelength of visible light?< Yes, it comes from that 'representative' wavelength of visible light, from the fact that the basic formula is related to the radius of the hole (not the diameter) and from the various conversions to millimetres. There are two or three 'focusing' effects associated with light passing through apertures and the main pinhole effect occurs between the two best known so it is a bit of a mix of effects in its own right. So if you were doing tests in a laboratory you would also see focusing at other distances than the ones predicted by that formula but the best one for pin hole cameras (and shadow sharpeners) is that one. It is all discussed in various works and was also I believe covered in a Scientific American in 1981. Patrick ------------------------------------------------------------------------- E-Mail: [EMAIL PROTECTED] Web: http://ourworld.compuserve.com/homepages/Patrick_Powers/ Lat: N 51d. 49m. 09s: Long: W 00d. 21m. 53s -
