filters for tungsten halogen lights question

Discussion in 'Digital Cameras' started by S Thomas, Jan 22, 2005.

  1. S Thomas

    S Thomas Guest

    I have set up two 500w tungsten halogen security type lights, in order to
    take digi photos of my collection. I bought a 'tent' thingy, the idea being
    that the tent diffuses the light so as to take decent pics without any
    background. It works fine, except that the pictures have a yellowy/brown
    cast. Is there any kind of filter or coating I can put on the lights to get
    rid of this cast? Or am I doomed to spend a heap of cash on spiffy


    El Terry
    S Thomas, Jan 22, 2005
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  2. S Thomas

    turbo Guest

    If its digital use 'white balance' to correct it.. Some details of your
    camera set up would help a lot though..
    turbo, Jan 22, 2005
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  3. S Thomas

    Ken Weitzel Guest

    Mxsmanic wrote:


    Wait a second... that presumes that gain can only
    be increased - never reduced.

    If you're taking a pic in a room with (can't turn 'em
    off) some red accent lamps, for instance, your pic
    will surely have a reddish cast to it.

    Have to fix it. So you (the camera)could increase the
    gain on the blue and green channels, and noise would
    certainly increase. Or, it could reduce the gain on
    the red channel, and noise would certainly decrease.

    Ken Weitzel, Jan 22, 2005
  4. S Thomas

    JPS Guest

    In message <cst5v3$2bt$>,
    You have to figure out how to get the proper color balance from your
    camera. There is really no need to use filters for this; warm halogen
    light is actually good for many digital camera; as good or better than
    white sunlight. Some cameras tend to under-expose in Halogen. Since
    you are shooting still objects, try positive exposure compensation as
    well, and compare results.

    Without mention of your camera, or the software you are using, it's hard
    to say how to correct the color cast.
    JPS, Jan 22, 2005
  5. S Thomas

    JPS Guest

    In message <>,
    Not necessarily! Most digitals are least sensitive to red light, and
    you get a more balanced S/N ratio when shooting under warm light. Many
    people report weak blue channels, but that is partly because cameras
    tend to under-expose with warm light, but boosting the exposure can get
    you a stronger blue channel, without clipping the red channel, because
    the red channel is usually least sensitive.

    The native color balance of most digitals is that white objects in white
    light come out Cyan or Green-Cyan. This is not daylight film, where
    white is white.

    Ideally, one could balance RGB in the light source, and use a balance
    that maximizes capture in each RAW channel. This would give the highest
    S/N at any given ISO, the cleanest shadows, and full usage of the bit
    JPS, Jan 22, 2005
  6. S Thomas

    JPS Guest

    In message <[email protected]>,
    Actually, lighting with a bias towards red is actually better at
    equalizing the channels for a greyscale subject with most digitals.
    Almost all CFA/sensor combos are least sensitive to red.
    JPS, Jan 22, 2005
  7. S Thomas

    JPS Guest

    In message <DLwId.17474$>,
    I have never heard of any digital camera that had a native white color
    balance. If you look at the list of multiplication factors in DCRAW.c
    for the red and blue channels, used to get daylight reference, the red
    channel is usually 1/2 to almost stop less sensitive than the green, and
    the blue varies from slightly more sensitive than green to 1/2 stop less
    sensitive. Cyan or cyan-green is the native color balance of most
    cameras. so a red or magenta-red light source is optimum for white/grey
    objects, if you want maximum saturation of each channel. So, sometimes
    filters will help, sometimes they can hurt, sometimes they will help one
    channel, but hurt another.
    JPS, Jan 22, 2005
  8. S Thomas

    JPS Guest

    In message <f8DId.17942$>,
    You'd probably have to A/B with and without filters, on the same screen,
    to see any differences. The main difference, theoretically, is that a
    filter will have different levels of attenuation at the extreme ends of
    the spectrum covered by each color filter in the bayer array, whereas
    software or firmware color correction will scale both ends of each
    spectrum the same amount.
    JPS, Jan 23, 2005
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