Bayer filter removal

Discussion in 'Digital Photography' started by David Dyer-Bennet, Apr 13, 2007.

  1. David Dyer-Bennet

    bugbear Guest

    Have you tried looking at the sort of kit
    the astronomers use?

    They like "high-sensitivity B&W camera for low-light situations"
    to a high degree :)

    bugbear, Apr 16, 2007
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  2. David Dyer-Bennet

    Martin Brown Guest

    Although there are comparatively few choices for high MP count. And
    they usually need to be tethered to a PSU and a computer. One such is
    the Kodak chip based 4Mpixel camera from Starlight XPress:

    You wouild want on with the two stage Peltier cooler disabled to get
    snesible battery life!

    Martin Brown
    Martin Brown, Apr 16, 2007
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  3. That, or specialized microscopy cameras aimed at things like
    fluorescence microscopy.

    In either case, you're not going to get something that's designed to
    work well in a stand-alone camera; these sorts of systems tend to prefer
    to be tethered to a computer and run off mains power.

    See, for example, and look at some of the
    various cameras under the products/Imaging cameras menu.

    Daniel Silevitch, Apr 16, 2007
  4. Maybe, but I'm *already* using 24/2, 58/1.2, 85/1.8, and 135/2 lenses.
    The 85 could be a stop faster or some such, and I could add a 28/1.4 or
    30/1.4 for various amounts of money (and the 30/1.4 is on the wishlist
    currently). I'm reasonably close to the limits in that direction already.

    IS wouldn't help much; I'm currently limited largely by *subject*
    motion. IS would simplify my shooting some, letting me use my current
    shutter speeds in a wider range of positions (not so much need for
    leaning against things!). But all the IS lenses I'm familiar with are a
    stop or two *slower* than what I'm currently using.
    I'd be happy with 6 megapixels, even 4 would be useful.
    Hadn't thought of the bleaching idea, but as you say it's high-risk.
    I'm not aware of one and nobody has pointed one out yet, no.
    David Dyer-Bennet, Apr 16, 2007
  5. But removing the IR filters probably remains undesirable (for a
    low-visible-light camera) because lenses don't focus IR and the visible
    spectrum close enough together to really want both at once; you really
    have to choose one or the other.
    David Dyer-Bennet, Apr 17, 2007
  6. It is best to use real data when making such estimates,
    rather than cartoon diagrams (although the has great
    explanations--just not enough info is given on the diagram).
    This Kodak data sheet gives more quantitative info:
    See pages 5, 17 (Figure 10), 18 (Figures 12).
    The green filter bandpass is about 75% transmission with a bandpass
    (called the Full Width at Half Maximum) FWHM = 0.07 microns.
    One needs to numerically integrate the area of that bandpass
    function times the IR filter spectrum times
    the solar spectrum (assuming the sun for the light source),
    times the quantum efficiency spectrum and compare that result
    with the same integration without the filters.
    Figure 1 here shows the solar spectrum through the earth's
    To first order the bandwidth of the solar spectrum * quantum
    efficiency ~ 0.35 microns, so if we assume the IR filter
    transmits ~80%, the increase by removing the filters would
    be: 0.35 / (0.07 * .75 *.8) ~ 8.3

    The factor of 50 I cited previously was from a thread where
    different cameras were being discussed and included different
    f/ratios between the lenses the systems used too, and compared
    to a back-side illuminated 95% QE detector, so that 50x
    included more factors than included here.

    So for current cameras, 8x or 3 stops is about what we can
    hope for by removing the Bayer and IR filters in current
    digital cameras, and another stop increase with higher QE

    Roger N. Clark (change username to rnclark), Apr 17, 2007
  7. Not necessarily: For low-light work under incandescent or candlelight or the
    like, the incident spectrum will be heavily tilted to red and IR, and I'd
    think that red and IR wouldn't be as bad for focus discrepancy as IR would
    be in landscape work. But even in landscape work, one is often stopped way
    down, so it might not be that much of a problem.

    But one is going to want to borrow some IR cut filters from the Leica M8
    folks at least some of the time...
    David J. Littleboy, Apr 17, 2007
  8. David Dyer-Bennet

    ASAAR Guest

    Why so dismissive ("cartoon diagrams")? The illustrations were
    actually done quite well and serve the intended purpose, which was
    to explain and educate, not to display precise measurements.

    This is probably of more interest to David. Your reply, that is,
    not Kodak's PDF file. Thanks for the link. The different filters
    show quite different quantum efficiencies than was shown in FSU's
    chart. Kodak's paper is an example where extensive data for their
    KAI-11002 sensor serves a purpose. My reply was intended only to
    provide David with the chart which might help him to decide if his
    estimate of the degree of filter attenuations were "ball park"

    A camera with a 3 stop improvement would have a small but
    significant number of photographers salivating and reaching for
    their credit cards and checkbooks. I'd hope that the use or removal
    of the IR filter would not be decided by the manufacturer but would
    be an easily changed option controlled by the photographer.
    ASAAR, Apr 17, 2007
  9. Hmmm, yes, true, red will predominate pretty heavily, and IR will very
    likely focus closer to red than to blue with pretty much any lens.

    Since my original reason for asking for this camera was for low-light
    work, being stopped way down is not on my radar :).
    I might need a red-and-infrared-pass filter for optimum results.
    David Dyer-Bennet, Apr 17, 2007
  10. Drooooool!

    Yes, having control of the IR filter would be nice. While IR isn't my
    main interest here, I *do* have some interest in IR and if I happened to
    get good capabilities there at the same time, that would be very nice.
    David Dyer-Bennet, Apr 17, 2007
  11. David Dyer-Bennet

    Martin Brown Guest

    OK. How about a lateral thinking solution then - from low light
    wildlife photography.

    Using a camera with the IR filter removed and then buy a very high
    quality infrared lowpass filter for your flashgun and no-one will ever
    see the flash. Something like Schott RG820 ought to be enough, maybe
    RG850 would be better. Then you can freeze motion reliably and there
    is no visible flash to startle the subjects and with flash you can
    have some half decent depth of field.

    You might even be able to get away with a crude IR pass plastic filter
    like unexposed slide film for a quick trial.

    Martin Brown
    Martin Brown, Apr 17, 2007
  12. Those terms are unknown to Google. Wow! Are those flash models, or
    filter designators?

    Yes, something like that might be a usable solution. It doesn't give
    the ambience of the event as well, which is a drawback, but not a fatal
    Do the converted cameras have a visible-blocking filter in place
    internally? If not I'd need one externally, which would blank out the
    David Dyer-Bennet, Apr 17, 2007
  13. David Dyer-Bennet

    ASAAR Guest

    Filters, apparently. Maybe RG820 was a typo, because that
    produced hits for electronic components, sprinklers and other
    things. But searching for RG850 got many hits for filters and only
    one for a sprinkler, at least on the first page. :) A sampling:
    ASAAR, Apr 17, 2007
  14. [A complimentary Cc of this posting was sent to
    David Dyer-Bennet
    Irrelevant. With any half-decent lens, red and blue will focus at the
    same plane. :-( ;-)

    Hope this helps,
    Ilya Zakharevich, Apr 19, 2007
  15. [A complimentary Cc of this posting was NOT [per weedlist] sent to
    Ilya Zakharevich
    I looked through my records, and can't find this link (I think it was
    Roger who cited it a year or two ago). All I can find is the
    "normalized" QE curves on

    and the absolute data for the peak QE on

    I remember there was a place where the approach of the latter
    reference (tunable LED [laser?] calibrated on a spectrophotometer, or
    somesuch) was used, and they provided the actual curves (not peak
    values, as with this reference)... Unfortunately, I can't find it now...

    Anybody with such a data at hand?

    Ilya Zakharevich, Apr 19, 2007
  16. [A complimentary Cc of this posting was sent to
    Roger N. Clark (change username to rnclark)
    This is in accordance to what I was claiming about 2 years ago, when
    my calculations have shown that digital cameras (of that time) worked
    at about 5-10% "throughput QE". However, these calculations where
    based on (flawed) data Roger put on his website; my current estimates
    of the same number are closer to 14%.

    Which means that no amount of tinkering can bring a gain above about 3
    stops. (In particular, the Bayer filter itself eats about 1.5stops of
    the signal.)

    Hope this helps,
    Ilya Zakharevich, Apr 19, 2007
  17. Yeah, well, reasonably close, certainly.
    David Dyer-Bennet, Apr 20, 2007
  18. Heees BAAAAACK!

    As usual, you come in with sweeping conclusions and broad
    accusations but supply zero evidence either for your case
    or what you are accusing others of.

    What flawed data?

    Last I remember you were arguing for pixels way smaller than
    a micron for which we calculated that a pixel would get
    only a photon or so per pixel in an average exposure.

    I also remember you being adamant about the QE of digital cameras
    being extremely low, well below 1 percent. So now you are claiming
    more reasonable levels. Why the change? I find it interesting
    that you say flawed data but then cite similar numbers from
    my studies.

    Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency

    You might also catch up on a lot of data since you last graced us
    with your presence in this newsgroup; see:

    Also see some of the references, including the more recent
    Kodak sensors which show a wealth of information, and note that
    the data from sensor manufacturers, like Kodak, the astrosurf
    pages by Christian Buil, mine, and others are in agreement.
    So again, what flawed data are you talking about?

    Roger N. Clark (change username to rnclark), Apr 23, 2007
  19. See:

    Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency

    Roger N. Clark (change username to rnclark), Apr 23, 2007
  20. [A complimentary Cc of this posting was sent to
    Roger N. Clark (change username to rnclark)
    Sorry, do not see anything relevant. Do you mean a some particular
    link on this page?
    You mean pp.17-etc? Thanks, these are very interesting (especially
    angular sensitivity curves!). Unfortunately, these are, obviously,
    not in-camera-performance values, thus have "only theoretical
    interest". ;-) E.g., I'm not sure they include IR filter and AA

    The data I meant were measured in-camera...

    Ilya Zakharevich, Apr 23, 2007
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