filters for tungsten halogen lights question

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

  1. S Thomas

    S Thomas Guest

    Hi
    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
    lighting?

    Cheers

    El Terry
     
    S Thomas, Jan 22, 2005
    #1
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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..
    "S Thomas" <> wrote in message
    news:cst5v3$2bt$...
    > Hi
    > 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 lighting?
    >
    > Cheers
    >
    > El Terry
    >
     
    turbo, Jan 22, 2005
    #2
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  3. S Thomas

    Mxsmanic Guest

    S Thomas writes:

    > 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
    > lighting?


    You can use a filter on the camera to correct the color cast, such as an
    80A. This works for both digital and film. On a digital camera, be
    sure to use the automatic or manual white balance as well, after
    mounting the filter.

    On a digital camera, you can also use white balance adjustment alone,
    without a filter, although the results won't be as good as images shot
    through a filter. With film, you can use tungsten-balanced film, which
    is already designed for tungsten lighting and doesn't require a filter
    (but such film is relatively hard to find and is often quite slow).

    As a last resort, you can correct the cast in Photoshop in the resulting
    images, but this doesn't provide results as clean as the methods above.
    The best results come from a filter on the camera or tungsten-balanced
    film.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jan 22, 2005
    #3
  4. Mxsmanic wrote:
    > S Thomas writes:
    >
    >> 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 lighting?

    >
    > You can use a filter on the camera to correct the color cast, such as
    > an 80A. This works for both digital and film. On a digital camera,
    > be sure to use the automatic or manual white balance as well, after
    > mounting the filter.
    >
    > On a digital camera, you can also use white balance adjustment alone,
    > without a filter, although the results won't be as good as images shot
    > through a filter.


    That would depend on several factors. Do you know this from personal
    experience or other evidence?

    I wonder if there is a real difference and if it is the same for all
    cameras? I have not done any serious testing, but some casual results from
    my current digital indicates that the difference is not great, if at all.
    But then I have not really checked. My results indicate that given a chance
    with the right subject or manual setting of white balance either sun or
    tungsten lighting results in very good results.

    > With film, you can use tungsten-balanced film,
    > which is already designed for tungsten lighting and doesn't require a
    > filter (but such film is relatively hard to find and is often quite
    > slow).
    >
    > As a last resort, you can correct the cast in Photoshop in the
    > resulting images, but this doesn't provide results as clean as the
    > methods above. The best results come from a filter on the camera or
    > tungsten-balanced film.


    --
    Joseph Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Jan 22, 2005
    #4
  5. S Thomas

    Mxsmanic Guest

    Joseph Meehan writes:

    > That would depend on several factors. Do you know this from personal
    > experience or other evidence?


    It's an engineering reality. White balance works by changing the gain
    on the red, blue, and green channels, which invariably increases noise.
    A filter works by removing the colors in the original scene that produce
    the color cast, and does not increase noise.

    For both film and digital photography, the best results come from
    filtering the light from the scene before it reaches the film or image
    sensor.

    > I wonder if there is a real difference and if it is the same for all
    > cameras?


    Since it is a basic principle of photography, it applies to all cameras.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jan 22, 2005
    #5
  6. S Thomas

    Ken Weitzel Guest

    Mxsmanic wrote:

    <snip>

    > It's an engineering reality. White balance works by changing the gain
    > on the red, blue, and green channels, which invariably increases noise.
    > A filter works by removing the colors in the original scene that produce
    > the color cast, and does not increase noise.


    Hi...

    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
     
    Ken Weitzel, Jan 22, 2005
    #6
  7. S Thomas

    Marvin Guest

    S Thomas wrote:
    > Hi
    > 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
    > lighting?
    >
    > Cheers
    >
    > El Terry
    >
    >


    Years ago, Sylvania sold a "Sun Gun" that had a tungsten halogon lamp on a mount designed to connect to a camera. I still
    have mine, and use it occasionally. The name implies that a sunlight setting should work. I don't get any kind of color
    cast when I use it. I generally bounce the light off a white ceiling; direct lighting would be harsh.

    It is not the same product as the Sun Gun at http://www.frezzi.com/mini-sun.htm.
     
    Marvin, Jan 22, 2005
    #7
  8. Mxsmanic wrote:
    > Joseph Meehan writes:
    >
    >> That would depend on several factors. Do you know this from personal
    >> experience or other evidence?

    >
    > It's an engineering reality. White balance works by changing the gain
    > on the red, blue, and green channels, which invariably increases
    > noise.


    I assume that to be correct, but that assumes the standard balance is
    daylight, and tungsten is an adjustment. Even your comment (changing) the
    gain does not indicate increase or perhaps decrease. It may well be that
    the neutral is between the two or even tungsten. It also does not address
    the question of materiality, so we adjust X amount what is the threshold of
    increased noise? Maybe 2X Is THIS noise been found to be a problem?

    Frankly I don't know, but I have not observed any, then again, I have
    not looked for it. So for casual use, with the two cameras I have owned, it
    has not been material for casual use.

    > A filter works by removing the colors in the original scene
    > that produce the color cast, and does not increase noise.


    However for critical use, that extra layer of glass can degrade the
    image. Over all I would say that it does not normally degrade the image in
    any material way for casual use, but it sure can for critical use, and that
    I have seen in my own work.

    Don't get me wrong. This may be a problem, I don't know, I was just
    trying to ask you if you really knew for studies or personal observation or
    if you were speaking from a theoretical position.

    >
    > For both film and digital photography, the best results come from
    > filtering the light from the scene before it reaches the film or image
    > sensor.
    >
    >> I wonder if there is a real difference and if it is the same for all
    >> cameras?

    >
    > Since it is a basic principle of photography, it applies to all
    > cameras.


    --
    Joseph Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Jan 22, 2005
    #8
  9. S Thomas

    Guest

    In message <cst5v3$2bt$>,
    "S Thomas" <> wrote:

    >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
    >lighting?


    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.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jan 22, 2005
    #9
  10. S Thomas

    Guest

    In message <>,
    Mxsmanic <> wrote:

    >On a digital camera, you can also use white balance adjustment alone,
    >without a filter, although the results won't be as good as images shot
    >through a filter.


    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
    depth.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jan 22, 2005
    #10
  11. S Thomas

    Guest

    In message <ZouId.141217$8l.137759@pd7tw1no>,
    Ken Weitzel <> 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.


    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.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jan 22, 2005
    #11
  12. S Thomas

    Guest

    In message <DLwId.17474$>,
    "Joseph Meehan" <> wrote:

    >I assume that to be correct, but that assumes the standard balance is
    >daylight, and tungsten is an adjustment. Even your comment (changing) the
    >gain does not indicate increase or perhaps decrease. It may well be that
    >the neutral is between the two or even tungsten.


    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.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jan 22, 2005
    #12
  13. S Thomas

    Mxsmanic Guest

    Ken Weitzel writes:

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


    Correcting color balance by reducing gain only significantly reduces the
    overall sensitivity of the sensor. It can be done, of course, but most
    cameras don't do it, and in any case, it would then be equivalent to
    using a filter (no better, but no worse).

    > 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.


    By increasing gain on one channel while reducing it on another, you
    maintain overall sensitivity to light, which is very convenient. It
    does produce more noise, though. Reducing gain alone is possible, but
    then you have to adjust the effective ISO and exposure.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jan 22, 2005
    #13
  14. S Thomas

    Mxsmanic Guest

    Joseph Meehan writes:

    > I assume that to be correct, but that assumes the standard balance is
    > daylight ...


    Daylight has a much flatter spectrum than tungsten light.

    > However for critical use, that extra layer of glass can degrade the
    > image.


    I doubt that most lenses or sensors/films would see the difference with
    a good filter.

    And if it's critical use, you sure won't be boosting the gain on any
    channels.

    > Don't get me wrong. This may be a problem, I don't know, I was just
    > trying to ask you if you really knew for studies or personal observation or
    > if you were speaking from a theoretical position.


    It's a mathematical inevitability. I don't know if it's a serious
    problem or not--that would depend on the circumstances and the camera.
    But if you want the best possible results, you should probably use a
    filter.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jan 22, 2005
    #14
  15. Mxsmanic wrote:
    > Joseph Meehan writes:
    >
    >> I assume that to be correct, but that assumes the standard balance is
    >> daylight ...

    >
    > Daylight has a much flatter spectrum than tungsten light.


    True, and the whole issue of spectrum really makes balancing
    difficult -- no lets say interesting. But it the curve does not really
    change the balance by itself.

    >
    >> However for critical use, that extra layer of glass can degrade the
    >> image.

    >
    > I doubt that most lenses or sensors/films would see the difference
    > with a good filter.


    I agree.

    >
    > And if it's critical use, you sure won't be boosting the gain on any
    > channels


    I'll take your word for it. I have little to no practical experience or
    solid information yet with that area.
    ..
    >
    >> Don't get me wrong. This may be a problem, I don't know, I was just
    >> trying to ask you if you really knew for studies or personal
    >> observation or if you were speaking from a theoretical position.

    >
    > It's a mathematical inevitability.


    Is it? I would guess if sensors are by design daylight balanced, that
    would be true, but are they? I don't know. It would seem from other
    responses they are not. Do you know?

    > I don't know if it's a serious
    > problem or not--that would depend on the circumstances and the camera.
    > But if you want the best possible results, you should probably use a
    > filter.


    I would give it a tossup based on what I know and what I must guess from
    lack of hard facts.

    --
    Joseph Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Jan 22, 2005
    #15
  16. S Thomas

    Mxsmanic Guest

    Joseph Meehan writes:

    > Is it? I would guess if sensors are by design daylight balanced, that
    > would be true, but are they? I don't know. It would seem from other
    > responses they are not. Do you know?


    Silicon has a broad spectral sensitivity that peaks in the infrared.
    Individual CCDs have variable sensitivities depending on their design
    but it is also fairly broad and I think it can be made fairly flat as
    well.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jan 22, 2005
    #16
  17. Mxsmanic wrote:
    > Joseph Meehan writes:
    >
    >> Is it? I would guess if sensors are by design daylight balanced,
    >> that would be true, but are they? I don't know. It would seem from
    >> other responses they are not. Do you know?

    >
    > Silicon has a broad spectral sensitivity that peaks in the infrared.
    > Individual CCDs have variable sensitivities depending on their design
    > but it is also fairly broad and I think it can be made fairly flat as
    > well.


    I believe it is a question of what negative effect (likely noise) might
    come about by adjusting white balance electronically v.s. using filters AND
    what type of lighting (generally daylight or tungsten) will produce the most
    of those negative effects.

    It seems we really don't have an answer to that question, but we have
    come up with a better idea of what that question may be and some of the
    factors we need to research to start adding to our knowledge in this area.

    It also seems that no one (certainly not me) has done any practical
    testing, to determine if the effect is sufficient to even worry about.

    I think it would be an interesting study, and if I were bored enough or
    I thought there was some serious reward for doing it I might, but I think I
    will leave that for someone else. Maybe someone with the right skills, and
    equipment to do it right.

    In any case it appears a little early to be saying that adjustments or
    filters are preferred at this time or even that there will be an real
    difference.


    --
    Joseph Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Jan 23, 2005
    #17
  18. S Thomas

    Guest

    In message <f8DId.17942$>,
    "Joseph Meehan" <> wrote:

    >I think it would be an interesting study, and if I were bored enough or
    >I thought there was some serious reward for doing it I might, but I think I
    >will leave that for someone else. Maybe someone with the right skills, and
    >equipment to do it right.


    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.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jan 23, 2005
    #18
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