Josh Koffman wrote, in part: >What if you used a prism instead of a filter? Then place the >photodetectors at the correct output angle. I'm puzzled by all this talk of prisms. A diffraction grating works much better, at least in all the (physics) applications I've worked with. Regarding another comment someone made, you *can* use a diffraction grating with a diffuse source, you just need to send the light through a slit and maybe some additional optics. Michael V Thank you for reading my little posting. _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads