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How to test cutoff frequency of IR filter on camera?

  1. Nov 7, 2013 #1
    Modern cell phones seems to come with IR filters on their cameras. I want to do an experiment to figure out what wavelengths these filters allow to pass and which they block. How would I go about doing this?
    Also, what sort of equipment would I need? I am a university student so I have access to a nicely supplied physics lab. Thanks.
     
  2. jcsd
  3. Nov 8, 2013 #2

    UltrafastPED

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    Remove the filter; using a broad-spectrum source (e.g., a tungsten lamp) take a spectrum.
    Now insert the filter and take another spectrum.

    This will show you the attenuation for all wavelengths, and those which are blocked completely.

    Your lab should have a well-calibrated light source and a spectrometer. If the equipment is modern it will be fiber coupled; if it is older there will be gratings inside, and you will have to use some optics to collimate the light into the spectrometer slit.
     
  4. Nov 8, 2013 #3

    Andy Resnick

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    Alternatively, use the output of a monochromator to illuminate the sensor, compare the monochromator output intensity with the image intensity to (approximately) determine the cutoff wavelength.

    You shouldn't have to go much beyond 700nm- no fancy IR equipment is needed. Same on the UV side- you should not have to go much below 400nm.
     
  5. Nov 8, 2013 #4

    UltrafastPED

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    We pop the filters off from cheap web cams so that they can pick up near infrared (700-850 nm or so) in our laser lab. But if you plan to put it back, you may prefer the non-destructive route.
     
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