All what stuff? Can you please make it a habit to quote the post that you are commenting on? And indicate that you have actually read any links suggested to you by saying what you do and do not understand in each? Lordy.I don't understand all that stuff.
Ir is light. What's the problem?I don't understand all that stuff. Can IR be focused? Or are its properties too different?
It all depends on which wavelength of IR you are interested in. In the 'old days' of film cameras, many of them had an alternative focus / distance setting so that you could use IR film 'blind'. So, in principle, it's fine - especially when you realize that many solid state sensors are so sensitive to IR that they have an IR filter stuck on the front of them. A bit more loss in the lens shouldn't affect results too much.I don't understand all that stuff. Can IR be focused? Or are its properties too different?
Thank you. This is what I wanted to understand. Wasn't sure if IR had different properties from visible light or if any material could focus as optical glass can, but outside the visible spectrum.IR can be focussed, just like other light, but a lens for IR imaging must transmit IR light. Most materials used for visible light block the far IR. That is why the lens for IR must be made from specially selected materials.
Since the refractive index, and so the focal length of a lens, is a function of wavelength, the focal point for IR will be in a slightly different place to that for visible light.
If you want a good focussing action over a wide bandwidth then you could do worse than using a paraboloid reflector with a metallic surface. The biggest optical and IR telescopes all use this method and so do radio telescopes, of course. Despite passing through most materials, X Rays can also be focussed with a metallic reflector - the only difference is that reflection only works at very oblique angles. An X Ray scope works this way (a highly 'offset' reflector)if any material could focus as optical glass can, but outside the visible spectrum.