Digital's sensitivity to near Infrared...

Discussion in 'Digital Photography' started by Leendert Combee, Nov 9, 2003.

  1. Some time ago there were some threads here and on alt.photography on
    the subject of making near-infrared photos with a digital camera: the
    ccd is sensitive to near-ir (what about cmos?) so in the absence of an
    IR blocking filter in (many/some?) digital cameras all it takes is a
    light blocking filter and one can take near-ir images. I was excited
    by the idea, tested my camera by pointing a remote to it and noted the
    bright flare on the lcd. Bought a light blocking filter and it all
    works very well. So far so good.

    But that made me thinking: if the ccd is sensitive to ir, then in a
    normal shooting mode in particular the red channel is going to pick up
    a good deal of near-ir which is going to distort the color balance in
    a fundamentally non-correctably way...? Especially for example foliage
    in a late evening sun? I noticed that on a normal sunny day there are
    about 5-6 stops of difference between the normal image and the near-ir
    image. This is very significant (maybe not for the p&s crowd, but for
    serious photographers it is something to think about). Should I now
    get a IR-blocking filter for better colour rendition? That may mess up
    again the colorbalance settings. Is there a trend towards build-in IR
    blocking filters in Digicams?

    Anyone any comments - I have rarely seen this subject discussed. I do
    not know of any website or even the manufacturers spec documents that
    list the presence of such filters.

    Leendert Combee
    www.geocities.com/nn_photo
    Leendert Combee, Nov 9, 2003
    #1
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  2. Leendert Combee

    gr Guest

    "Leendert Combee" <> wrote
    > But that made me thinking: if the ccd is sensitive to ir, then in a
    > normal shooting mode in particular the red channel is going to pick up
    > a good deal of near-ir


    Not necessarily just the red channel. The blue channel sometimes picks up IR
    as well. Remember, the color filters they put over the sensors block visible
    light, not infrared.

    > which is going to distort the color balance in
    > a fundamentally non-correctably way...? Especially for example foliage
    > in a late evening sun? I noticed that on a normal sunny day there are
    > about 5-6 stops of difference between the normal image and the near-ir
    > image.


    Are you sure it's only 5-6 stops? Most cameras fall in the 7-11 stops of
    difference range. But even so...

    > This is very significant (maybe not for the p&s crowd, but for
    > serious photographers it is something to think about). Should I now
    > get a IR-blocking filter for better colour rendition? That may mess up
    > again the colorbalance settings. Is there a trend towards build-in IR
    > blocking filters in Digicams?


    Don't worry about it. A digital camera only has about 6 stops of dynamic
    range anyway. The IR is completely lost in the visible light which massively
    over-exposes it.

    However, if you removed the IR blocking filter from the camera's CCD, then
    you'd have a concern.
    gr, Nov 9, 2003
    #2
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  3. Leendert Combee

    Ron Andrews Guest

    Here's a quick test to see if near IR sensitivity is affecting the
    color reproduction of your digital camera. Shoot a picture of a subject that
    reflects in the long red to near IR region. Heavenly blue morning glories,
    blue hydrangeas, and purple clematis are classic problems. If the blue
    flowers reproduce purple or if the purple clematis reproduces red violet
    rather than deep purple, then you have a problem. Since these flowers are
    out of season in most places, you could try shooting green pool tables. Many
    of them use a fabric dye that reflects in the long red region. If it shows
    up brown, you have a problem.

    --
    Ron Andrews
    http://members.hostedscripts.com/antispam.html
    Ron Andrews, Nov 10, 2003
    #3
  4. Leendert Combee

    jam Guest

    Leendert,

    When I first got wind of digital IR photography, I too worried about
    IR contamination. I no longer worry. Furthermore, I've come to the
    conclusion, after some testing, that IR-blocking filters do more harm
    than good. Practically speaking, digital IR contamination is only an
    issue when the scene includes objects at or near incansdescent
    temperatures. Few scenes do. For a longer discussion, see

    www.cliffshade.com/dpfwiw/ir.htm#contamination

    Of necessity, all digital cameras with silicon-based image receivers
    have internal IR cut filters (IIRCFs). Silicon sensors are as
    sensitive to NIR as they are to visible light, if not moreso. There
    has indeed been a trend toward ever more restrictive IIRCFs.
    Unfortunately, that makes for poorer and poorer IR performance with
    marginal gains in visible light performance. (My pet theory is that
    the filters have been made more restrictive primarily to benefit
    in-camera white balance algorithms.) My trusty Bronze Age Oly C-2020Z
    has great NIR sensitivity, but I have yet to find a compelling
    instance of IR contamination that doesn't involve a hot object, and
    I've been looking hard. I have no complaints with its white balance.
    --
    Jeremy McCreary
    Denver, CO
    www.cliffshade.com/dpfwiw/
    -------------------------------------------


    "Leendert Combee" <> wrote in message
    news:...
    | Some time ago there were some threads here and on alt.photography on
    | the subject of making near-infrared photos with a digital camera:
    the
    | ccd is sensitive to near-ir (what about cmos?) so in the absence of
    an
    | IR blocking filter in (many/some?) digital cameras all it takes is a
    | light blocking filter and one can take near-ir images. I was excited
    | by the idea, tested my camera by pointing a remote to it and noted
    the
    | bright flare on the lcd. Bought a light blocking filter and it all
    | works very well. So far so good.
    |
    | But that made me thinking: if the ccd is sensitive to ir, then in a
    | normal shooting mode in particular the red channel is going to pick
    up
    | a good deal of near-ir which is going to distort the color balance
    in
    | a fundamentally non-correctably way...? Especially for example
    foliage
    | in a late evening sun? I noticed that on a normal sunny day there
    are
    | about 5-6 stops of difference between the normal image and the
    near-ir
    | image. This is very significant (maybe not for the p&s crowd, but
    for
    | serious photographers it is something to think about). Should I now
    | get a IR-blocking filter for better colour rendition? That may mess
    up
    | again the colorbalance settings. Is there a trend towards build-in
    IR
    | blocking filters in Digicams?
    |
    | Anyone any comments - I have rarely seen this subject discussed. I
    do
    | not know of any website or even the manufacturers spec documents
    that
    | list the presence of such filters.
    |
    | Leendert Combee
    | www.geocities.com/nn_photo
    jam, Nov 13, 2003
    #4
  5. Leendert Combee

    jam Guest

    Please see my comments at [] below.
    --
    Jeremy McCreary
    Denver, CO
    www.cliffshade.com/dpfwiw/
    -------------------------------------------
    "gr" <> wrote in message
    news:bomi02$1fb068$-berlin.de...
    | "Leendert Combee" <> wrote
    | > But that made me thinking: if the ccd is sensitive to ir, then in
    a
    | > normal shooting mode in particular the red channel is going to
    pick up
    | > a good deal of near-ir
    |
    | Not necessarily just the red channel. The blue channel sometimes
    picks up IR
    | as well. Remember, the color filters they put over the sensors block
    visible
    | light, not infrared.

    [] The Bayer filters variably pass shortwave NIR in the 700-770 nm
    range but all pass longwave NIR (770-1200 nm) equally. The shortwave
    stuff can mess up white balance in theory, whereas the longwave would
    just lighten the image across the board.

    | > which is going to distort the color balance in
    | > a fundamentally non-correctably way...? Especially for example
    foliage
    | > in a late evening sun? I noticed that on a normal sunny day there
    are
    | > about 5-6 stops of difference between the normal image and the
    near-ir
    | > image.
    |
    | Are you sure it's only 5-6 stops? Most cameras fall in the 7-11
    stops of
    | difference range. But even so...

    [] My Oly C-2020Z and several other 2MP cameras of its era usually
    come in at 5-6 stops, at least with an R72 IR filter, but recent
    cameras are likely to fall in the 7-11 stop range. My next camera will
    hopefully be an Oly E-1, but I'll always keep the 2020 for IR work.

    | > This is very significant (maybe not for the p&s crowd, but for
    | > serious photographers it is something to think about). Should I
    now
    | > get a IR-blocking filter for better colour rendition? That may
    mess up
    | > again the colorbalance settings. Is there a trend towards build-in
    IR
    | > blocking filters in Digicams?
    |
    | Don't worry about it. A digital camera only has about 6 stops of
    dynamic
    | range anyway. The IR is completely lost in the visible light which
    massively
    | over-exposes it.

    [] Agreed, as long as the scene contains nothing near incandescence.

    | However, if you removed the IR blocking filter from the camera's
    CCD, then
    | you'd have a concern.

    [] Some avid digital IR buffs like my friend Don Ellis at
    www.kleptography.com do just that with great results. The surgery's
    not for the faint of heart. The Sony F-707 and its successors have a
    NightShot mode wherein the filter's temporarily removed from the light
    path, but the implementation's somewhat crippled for daytime NIR work
    in order to discourage voyeuristic "x-ray" uses.
    jam, Nov 13, 2003
    #5
  6. Leendert Combee

    jam Guest

    Ron,

    Have you found consumer digital cameras that fail these tests?
    --
    Jeremy McCreary
    Denver, CO
    www.cliffshade.com/dpfwiw/
    -------------------------------------------

    "Ron Andrews" <> wrote in message
    news:_9Drb.79303$...
    | Here's a quick test to see if near IR sensitivity is affecting
    the
    | color reproduction of your digital camera. Shoot a picture of a
    subject that
    | reflects in the long red to near IR region. Heavenly blue morning
    glories,
    | blue hydrangeas, and purple clematis are classic problems. If the
    blue
    | flowers reproduce purple or if the purple clematis reproduces red
    violet
    | rather than deep purple, then you have a problem. Since these
    flowers are
    | out of season in most places, you could try shooting green pool
    tables. Many
    | of them use a fabric dye that reflects in the long red region. If it
    shows
    | up brown, you have a problem.
    |
    | --
    | Ron Andrews
    | http://members.hostedscripts.com/antispam.html
    |
    |
    jam, Nov 14, 2003
    #6
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