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  • Question about matching the lens to the detector

    From adamstrange8w7@gmail.com@21:1/5 to All on Tue Aug 4 10:08:22 2020
    I am designing an infrared lens to work at 10 microns. I have a detector with a 12 micron pitch and a system maximum aperture of 95 mm. What would be the optimum focal length for this lens?
    I realize that it is best to have two pixels across the Airy disk, which would mean this system should a focal length of 80 mm.

    However, the customer wants the resolution equivalent of a diffraction-limited system with a focal length of 200 mm, which of course is not happening with this aperture and this detector pitch, but I was wondering if there is some optimum value for a
    mismatch between the lens and a detector? Some focal length which would allow the unresolved details of the scene to best be extracted?

    The system will be taking several images of the scene, and they could, theoretically, be combined to increase the level of detail.

    Thanks in advance for your replies.

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  • From Phil Hobbs@21:1/5 to adamstrange8w7@gmail.com on Wed Aug 5 06:48:14 2020
    On 2020-08-04 13:08, adamstrange8w7@gmail.com wrote:
    I am designing an infrared lens to work at 10 microns. I have a
    detector with a 12 micron pitch and a system maximum aperture of 95
    mm. What would be the optimum focal length for this lens? I realize
    that it is best to have two pixels across the Airy disk, which would
    mean this system should a focal length of 80 mm.

    At some point the FOV has to come into the equation. Otherwise you can oversample the image as much as you want.


    However, the customer wants the resolution equivalent of a diffraction-limited system with a focal length of 200 mm, which of
    course is not happening with this aperture and this detector pitch.

    Why not? The FL just determines what the angular subtense of each pixel
    is. The image-side numerical aperture is what determines the maximum
    available resolution for a given wavelength.

    but I was wondering if there is some optimum value for a mismatch
    between the lens and a detector? Some focal length which would allow
    the unresolved details of the scene to best be extracted?

    Professional astronomers with relatively deep pockets often use four
    pixels per cycle at Nyquist. Amateurs have to trade off the diameter
    and FOV of the scope (which determine the image NA) vs. the available
    budget.


    The system will be taking several images of the scene, and they
    could, theoretically, be combined to increase the level of detail.

    Thanks in advance for your replies.


    Cheers

    Phil Hobbs
    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

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