Film and 1000-2000 nm Broadband Antireflection Coatings 1000-2000 nm

Discussion in 'Camera Building, Repairs & Modification' started by Mustafa Umut Sarac, Feb 16, 2013.

  1. Mustafa Umut Sarac

    Mustafa Umut Sarac Member

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    I have a catalog for ordering lens elements and coatings. There are 3 AR Coatings. 350-700 , 800-1100 , 1000-2000.

    If I order 12 dollars 1000-2000 nm antireflection coating , does that coating blocks other wavelenghts ?

    If it does block , do ordinary BW Film sees that wavelenght portion and what images would look like ?

    Mustafa Umut Sarac
    Istanbul
     
  2. polyglot

    polyglot Member

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    No. The coating blocks reflections by wave-cancellation inside the coating layer because it's 1/4 wavelength thick. The reflected ray from one side of the coating is 1/2 wave out of phase with the reflected ray from the other side and they cancel.

    If the wavelength is wrong, they don't cancel. If the wavelength is twice as long, it will constructively interfere and you've just built a more-efficient mirror!

    1000-2000nm is deep IR. Visible is 350-700nm, which means the 1000-2000nm coating will do nothing or maybe make reflections worse. You need the 350-700 version if you want it to work in the visible band.

    Capturing 2000nm (2um) IR requires a cooled sensor and optics. You're not going to do it with chemical film - if it were sensitive to those wavelengths then it would expose itself as soon as it (or the container or camera its in) reached room temperature.