Infrared (IR) cameras can focus IR radiation similarly to how visible light cameras focus visible light, but they require specialized lenses made from materials like germanium or zinc sulfide that transmit IR light. Standard glass lenses block far IR wavelengths, necessitating the use of these specific materials for effective focusing. The focal point for IR differs slightly from that of visible light due to variations in refractive index based on wavelength. Additionally, paraboloid reflectors are recommended for wide bandwidth focusing, eliminating chromatic aberration.
PREREQUISITESOptical engineers, infrared camera manufacturers, and anyone involved in the design and application of infrared imaging technology will benefit from this discussion.
Baluncore said:
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.LightningInAJar said:I don't understand all that stuff.
Ir is light. What's the problem?LightningInAJar said: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.LightningInAJar said: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.Baluncore said: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)LightningInAJar said:if any material could focus as optical glass can, but outside the visible spectrum.