Josh Koffman gmail.com> writes: > > On 2/28/07, Alan B. Pearce rl.ac.uk> wrote: > > Hmm, halogen lamps do the opposite to allow the heat to go out the back > > while sending the visible light out the front ... > > Aren't you talking about dichroic "cold mirrors"? The halogen cycle > doesn't really have anything to do with where the heat goes, just that > there is enough to allow the filament to redeposit on itself. At least > that's what I recall. Help? Yes that's it. The glass must be hot or the halogen cycle won't work. The non-dichroic mirror then produces a second focal point for the hot glass. This can destroy casings and optics so the dichroic mirror had to be invented. Peter P. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist