> No, or maybe. Leaving aside matters of absorption or reflection (that's why > only half makes it through), even if the light were somehow recycled to again > attempt to pass through the filter, only half of the remaining light would be > able to pass through the filter at any one time, ad infinitum. Well, maybe not half ... the parts of the light that didn't make it through the first time are less likely to succeed on subsequent occasions. The question is not as daft as it sounds. If the filter works by absorption then obviously the light has ceased to be. If by reflection - it can be wavelength specific. Each time the light tried to get back through it would have less and less chance ... What is light anyway and how do you know when you only have half of it? There is absolutely no such thing as a perfect ND filter for a start. When you measure the light you introduce yet more problem ... light is (was before dumbing down) by definition visible. But instruments measure the energy and respond ... well, try to respond ... Try to measure dark. _______________________________________________________________________ Freeserve AnyTime, only £13.99 per month with one month's FREE trial! For more information visit http://www.freeserve.com/time/ or call free on 0800 970 8890
