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Thread: How to set uniWB with the A900

  1. #1
    Senior Member douglasf13's Avatar
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    Dec 2008
    Los Angeles, California, USA
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    How to set uniWB with the A900

    I got a couple of requests for this, so I decided to start a new thread

    Setting uniWB with the A900 (and A700) is quite easy. You essentially assign a blown out white balance setting to one of your three custom WB slots. Here is how:

    Setup the camera to take a custom WB as per manual. When you fire the camera, overexpose the shot as much as possible. ie. Aim it at a bright light source with a very wide aperture and slow shutter speed (i used iso 800,) so that the camera fully blows out the whole image. The type of light doesn't matter.

    You should get around 3500k G9**. The camera will tell you that there is an error, but ignore that and set the new WB to one of your 3 slots. Now, all of your RAW shots will appear green with this uniWB (obviously you don't want to use uniWB with jpeg,) but it will give you an accurate portrayal of the camera's actual RAW histogram, rather than the camera jpeg histogram, and you'll find that the green channel is nearly always the first to blow, which makes sense because of the R,G,B,G bayer filters.

    Also, it seems these may be the best jpeg settings to get your camera lcd neutral:
    - aRGB
    - neutral CS
    - contrast -3
    - saturation -1
    - brightness -3

    Now, another caveat to this is that you'll have to play with your RAW converter of choice to take advantage of your exposures with uniWB, because most converters add lots of adjustments on import. I have to set the tone curve in C1 from "film like" to "linear," or things appear blown out. With ACR, (according to a kiklop of dyxum) flatten the tone curve, set brightness and contrast to zero and add -0.35 EV (hidden baseline exposure correction) for a900 files to get close.

    I hope this long post makes sense, and feel free to ask me questions. Good luck!

    **do not just dial in a white balance setting with manual WB. It provides a different result that isn't uniWB, so do it the way I described

  2. #2

    Re: How to set uniWB with the A900

    thanks Douglas,

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