5,600k correction for low light

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asdv
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Joined: Jun 27 2003

Chuck me out if I'm in the wrong forum.

Anyone know about using the 5,600k correction in camera menu instead of using the optical internal 5,600k filter, to gain advantage in low light ?

I can guess it might not be a good idea but I don't really know why.

Alan Roberts
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Joined: May 3 1999

It depends on the camera design.

Cameras are specified with (about) P3200 illuminant, sensitivity and noise are quoted for that. If you move outside and use an optical filter to rebalance, then the camera gains and noise don't change. But if you re-balance to the daylight without a filter, the blue gain goes down and red gain goes up, so noise near black takes on a pink hue. Also, you're using some of the highlight handling capability (up to a stop) to provide the extra gain needed in red, so you lose exposure range.

If you use the D56 mode, the camera r/b gains are changed by prescribed amounts to achieve what you did manually, with the same effect. Normally you can get away with it, and it saves messing about with filters. But if you're operating in low light and need extra gain, the pink shift in noise may be a problem; when working with extreme contrast you might notice the reduction in exposure range, this might appear as a colour cast in clipped highlights if you've used a prescription gamma that copes with it.

Does that make sense? I generally advise against it, use filters like you would with film.

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asdv
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Joined: Jun 27 2003

Yes I think I'm there. You're forcing the camera/sensor away from it's optimal range plus it leaves you prone to further problems.

I was thinking Varicam, Digibeta and DSR450 designs. But the DSR450 has no internal optical filters so maybe it's fundamentally different.

But how does it compare as a last resort and when the only alternative is to switch in some overall gain (when some image is better than nothing) ?

Alan Roberts
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If you have no alternative, fine, go ahead. Presumably the noise is olow enough not to be a problem, and nobody's dived into the menus to scrape the last bit of contrast handling. So there should be enough in-hand to do it.

The important thing is that you understand what's going on.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Joined: Jul 18 2003
asdv wrote:
But how does it compare as a last resort and when the only alternative is to switch in some overall gain (when some image is better than nothing) ?

Don't know about the 450, but with a DSR500 it works quite well in practice, and can often get one out of a hole especially around dusk. If the lights good, then for all the reasons Alan says (excessive gain in the red channel v that in blue) you should use an orange filter in daylight and balance through that, but in fading light when you need as much as possible it's a valid thing to do. Sometimes the camera may not take it and give an error message if the colour temperature is too high - a trick then is to use a little bit of blue balanced headlight to bring the reference back within range. The resulting picture will then obviously go a little cold, but normally given the reasons for wanting to do this, that's often not too bad a thing.

Alan Roberts
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There you go, the theory and the practice, all together :)

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

asdv
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Joined: Jun 27 2003

Excellent. Thank you both very much.

Alan Roberts
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Joined: May 3 1999

It's a pleasure, what we're here for :)

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.