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lighting & cameras

Discussion in 'Lighting and Electrics' started by benintights, Mar 4, 2004.

  1. benintights

    benintights Member

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    Hi,

    At our theatre/church we have cameras that display live shots of action occuring on stage. Recently we upgraded to better cameras, but being "better," they also turned out to be extremely sensative to lighting. Our theatre has a mix of ellipsoidals, parcans, and fresnels. Usually the center stage looks extremely bright on film, with the sides dim (for the live show no one could even tell the difference). When we enlarge the iris or turn up the gain on our cameras, the speaker on CS looks so bright he could pass as a ghost. Any ideas on what type of fixure or method would equalize the lighting across the stage?

    Thanks, :)
    benintights
     
  2. Nephilim

    Nephilim Active Member

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    If it's a standard CCTV or industrial camera, low-light or not, it's going to pick up unevenly. Your eyes are the best judge. If you were lighting for a camera shoot, that's a different question. But since you're lighting for a live audience, screw the camera.
     
  3. wemeck

    wemeck Active Member

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    I assume you are talking about video equipment. If so then depending on what type of gear you have you may have to white balance the cameras. If we are talking low-end equipment you might want to use a filiter to tone down the intensity.
     
  4. Nephilim

    Nephilim Active Member

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    That's true, an ND filter could help you out. Neutral Density; it's a grey filter that lowers the overall intensity letting have a better aperture.
     
  5. RonaldBeal

    RonaldBeal Active Member

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    The human eye has an amazing ability to "auto iris" between extremely different contrast ratios, based on what it is looking at. Video cameras, on the other hand aren't as smart. Different cameras have different dynamic ranges (usually measured in F-stops.)
    The heart of the problem is the Center Stage area IS BRIGHTER than the sides. Even though you may not notice it live, it is indeed the case. If you can find a used spot meter on Ebay (or even a used incident light meter) you can get a quantative measurement of how much of a discrepancy there is. Consumer cameras usually have 3-4 stops of dynamic range. Prosumer cameras: 4-5 stops, Pro cameras 6-7 stops, Film as hi as 12 stops.
    I think adding an ND filter will end up giving the same results as turning down the gain, you will still lower the over all level, but still won't reduce the contrast ratio. There are several filter options available though. A center weighted graduated ND. This is essentially a filter that is darker in the center, and gets lighter towards the edges. the down side is the camera must be fixed with the CS area in the center of the shot (where the darkest part of the filter is)
    A second option is using a low contrast filter. (these look sort of like a black net/grid) These can reduce the over all contrast of a scene by up to a full stop, however they also soften the image a little bit.
    Finally, (and in my opinion, the best solution,) is to normalize the lighting levels. Bring down the levels of the CS area to be closer to the side levels. If needed, gel the CS fixtures with a 1/4 or 1/2 CTB to correct for the lower color temp. You can also gel the fixtures with ND, so you can still bring the fixtures to full, with out blowing your contrast ratio. (ND .3 = 1 stop, ND .6 = 2stops, ND .9 =3 stops, etc...)
    As for the comment " But since you're lighting for a live audience, screw the camera." I believe you can get good quality images for the camera with out compromising the live shots. (the reality is if you match contrast ratios more closley, it will look better on camera, and the audience will not notice anything different.) It is a little more work, but the practice and experience is invaluable, and if you are a lighting person who can make an event look good live AND on video, and your competition can't, you've become significantly more marketable.
    Hope this helps
     
  6. dj_illusions

    dj_illusions Active Member

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    Someone taught me once that to white ballance, you put a white piece of paper, just your average printer paper and a light behind it, but not very bright and run the white ballance on the camera. Try to set the light so the paper looks the colour of the persons skin is appearing in the camera, and it should eliminate this problem!!

    We run into this alllll the time with video projection, and I have done this a few times and found it to be the most effective method!
     
  7. RonaldBeal

    RonaldBeal Active Member

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    A minor correction to Jeremy's description of how to white balance. Most cameras (video and digital still cameras) have a manual white balance, as well as several presets and auto. White balancing essentially tells the camera what "white' should be, and then the cameras electronics adjust the red, blue and green sensitivity levels accordingly. Auto white balance has the camera "guesses" based on some algorithims the cameras mfg came up with, (based on average light and subject conditions.) The most common presets: Indoors (a lightbulb symbol) , Sunlight (a sun symbol), Overcast outdoors (a symbol with clouds), and flourescent (a horizontal rectangle supposed to look a flourescent light tube). Some cameras may have other presets.
    Finally there is the manual white balance setting. to properly manual white balance you should zoom in and focus on a white card or paper lit by the same lights lighting your key subject (I.E. Center Stage podium.) Then you hit the manual white balance button and the camera adjusts accordingly. The paper or card should look white.

    Common mistakes white balancing:

    1: Not using the same kind of light as your key lights: If your key light is a discharge lamp (like many arc follow spots) and you white balance to an incandescent ellipsoidal, your images will look very blue. Likewise if you balance to the arc, and your key light is incandescent, the video will be yellow.

    2: Mixing lights of different color temps. I.E. using arcs and incandescents both to keylight the subject. the solution to this is to color correct one of the fixtures (usually the arcs with a full CTO: Lee 205)

    3: Balancing to a paper that isn't white. If you use a yellow paper, the camera will subtract yellow from the images and everythhing will appear blue. Another related problem is reflected color. If you are using the proper light on a white paper, but the paper is next to a yellow wall, that wall may reflect yellow onto the paper, altering your white balance. If you get a chance, play with white balancing on different surfaces to see the results.

    4: Balancing to a light with colored gel. If you use a ParCan with a red gel, you probably want the subject to look red. If you balance to that light with the gel still in, your camera will try to make red look white. Pull the gel, balance, then re-gel.

    5: Balancing without filters. If you use filters on the camera, balance with the same filters you will be using, otherwise the filters will tint the image (unless that is a particular effect you want. The exception is with some polarizing filters. You should balance, then put the polarizer on.

    Ultimatly, the fixtures you describe, (pars, fresnels and ellipsoidals) are all incandescent and have a color temperature of 3200K. Using the "indoor" or "incandescent" white balance preset should work. The exception to this is if there are large windows letting lots of sunlight in. Sunlight color temp varies from 2000K to 10000K depending on time of day and cloud cover. In that case you are best off manually white balancing each time you use the cameras.

    Hope this helps
     
  8. dj_illusions

    dj_illusions Active Member

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    Great information there... sorry mine was very vauge.... never really had much to do with video camera's and stuff, that was just something id picked up along the way lol
     
  9. Nephilim

    Nephilim Active Member

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    Wahey, a veritable video god. I'll be picking your brains :D

    The thing is ronald, the camera they've installed is a monitoring camera only (as far as I can tell), and as such the image on it does not matter nearly as much as what the human eye sees on stage. Still, fantastic advice :)
     
  10. benintights

    benintights Member

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    Great information, thanks guys. The other thing I really need to ask though is what type of lighting will be effective more for the live-video and stage. You all gave great tips on eqalizing the light from the view of the cameraman --now, from the view of the lighting technician?

    Appreciate the help.
    benintights
     

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