Coolpix 950 infra red characteristics

Discussion in 'Digital Photography' started by Tobit, Sep 26, 2003.

  1. Tobit

    Tobit Guest

    I am currently carrying out tests into the use of digital cameras for infra
    red reflectography/ photography, for the examination of historic paintings.
    I am currently using a Coolpix 950 for the low resolution tests. I need some
    tec. details about the 950 and Nikon have been v unhelpful. So I've got a
    couple of questions for the group.

    1. The Coolpix 950 has a 2.5mm IR filter mounted in front of the CCD. Does
    anyone know the technical specification for the this IR filter so that I can
    assess how much this is effecting our results. (i.e. what wavelength does it
    absorbe/ pass)

    2. Does anyone know the highest frequency at which the CCD is sensitive to
    IR radiation. I understand that a number of CCDs are cease to register at
    above 1000nm. Is this the case for the one used in the Coolpix 950 ?

    Many thanks for your help

    Tobit Curteis
    ___________

    Cambridge
    UK
     
    Tobit, Sep 26, 2003
    #1
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  2. snip

    There's an illustrated web article describing how to remove this filter plus
    other info, which I downloaded some time ago.

    Do a search for "Removing the IR Blocking Filter in the NikonĀ® 950 and 990"
     
    Malcolm Stewart, Sep 26, 2003
    #2
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  3. Can't help there I'm afraid, but a word of warning, if you manage to get
    hold of figures for a later Coolpix, don't assume they'll be the same.
    The 950 is considerably more sensitive to IR than both the 995 and 4500.
     
    Willy Eckerslyke, Sep 26, 2003
    #3
  4. Tobit

    Ian Stirling Guest

    I think you mean lowest frequency.
    Anyway, IIRC, no silicon based detector have fallen off very significantly
    at 1000nm.
    For example, looking at the ICX249AL, a sony CCD designed for mono imaging,
    with enhanced IR sensitivity, it's down at 5% of it's max sensitivity (620nm)
    at 1000nm. (rising with a little sag almost linearly from there to 620nm)

    Your best results will be with black and white cameras, or at least removing
    the IR cut filter, and then using external bandpass filters.
    If you can totally exclude visible light, then using a IR source should
    work if it's bright enough.
     
    Ian Stirling, Sep 26, 2003
    #4
  5. Tobit

    Tobit Guest

    Removal of the blocking filter on the CCD and use of a bandpass filter at
    approx. 780nm gives very clear and bright mono images, suggesting a
    reasonable sensitivity in near infra red. I am interested in comparing our
    results to those achieved with infra red reflectography , hence the query
    about the CCD sensitivity. Where did you get the info about the Sony CCD ?

    --
    Tobit Curteis
    ___________

    Cambridge
    UK
    thing??"
     
    Tobit, Sep 29, 2003
    #5
  6. Tobit

    Ian Stirling Guest

    http://products.sel.sony.com/semi/PDF/ICX249AL.pdf

    At 780nm, nearly all silicon detectors will show significant response.
    The above chip is at 45%, some sensors (for example the one in my cheapest
    webcam without the filters, the OV7610) peaks at 800nm, and is still above
    10% out at 1200nm. (it's overall sensitivity is lousy though, and may be
    absolutely less sensitive than the CCD).



    --
    http://inquisitor.i.am/ | mailto: | Ian Stirling.
    ---------------------------+-------------------------+--------------------------
    "Melchett : Unhappily Blackadder, the Lord High Executioner is dead
    Blackadder : Oh woe! Murdered of course.
    Melchett : No, oddly enough no. They usually are but this one just got
    careless one night and signed his name on the wrong dotted line.
    They came for him while he slept." - Blackadder II
     
    Ian Stirling, Sep 30, 2003
    #6
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