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Author Topic: Is it possible to go below 2800K?  (Read 2382 times)

dreed

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Is it possible to go below 2800K?
« on: September 30, 2016, 11:58:32 am »

Recently I purchased a red LED flashlight to do some night time shooting of animals without disturbing them with the light. Unfortunately it turns out that the red light from the LED flashlight is too red for LR (or ACR) to be able to handle. If I move the white balance down to 2800K, I still have a predominately red image. This is in contrast to using (say) red cellophane in front of a normal torch which has a correctable temperature.

I suppose there are a couple of questions here, such as..
- is it possible to go below 2800K with other raw processing tools?
- why does ACR/LR set 2800K as the minimum?
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scyth

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Re: Is it possible to go below 2800K?
« Reply #1 on: September 30, 2016, 12:17:54 pm »

Recently I purchased a red LED flashlight to do some night time shooting of animals without disturbing them with the light. Unfortunately it turns out that the red light from the LED flashlight is too red for LR (or ACR) to be able to handle. If I move the white balance down to 2800K, I still have a predominately red image. This is in contrast to using (say) red cellophane in front of a normal torch which has a correctable temperature.

I suppose there are a couple of questions here, such as..
- is it possible to go below 2800K with other raw processing tools?
- why does ACR/LR set 2800K as the minimum?

read DNG PE manual = http://wwwimages.adobe.com/content/dam/Adobe/en/products/photoshop/pdfs/cs6/DNGProfile_EditorDocumentation.pdf = "Tutorial 4: Infrared-Modified Cameras and Unusual Lighting"

> why does ACR/LR set 2800K as the minimum?

just for convenience of ACR/LR UI for mass users... as noted for special cases you can modify profiles (the matrices that control how actually WB is calculated)
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fdisilvestro

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Re: Is it possible to go below 2800K?
« Reply #2 on: September 30, 2016, 06:44:49 pm »

I think your issue is related to the spectrum and not to white balance. Red LEDs have a very narrow spectrum and the only thing you achieve by changing WB is reducing the exposure.

scyth

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Re: Is it possible to go below 2800K?
« Reply #3 on: October 01, 2016, 01:08:33 am »

I think your issue is related to the spectrum and not to white balance. Red LEDs have a very narrow spectrum and the only thing you achieve by changing WB is reducing the exposure.

that is certainly true because WB is ~ per channel exposure correction (albeit in ACR/LR after demosaick) ... however he might hope that there are still some data in the other channels (may be his camera has CFA that allows enough light from that Red LED into "blue" and "green" sensels) so general exposure push after WB brings "red" channel down + decent dose of NR
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dreed

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Re: Is it possible to go below 2800K?
« Reply #4 on: October 01, 2016, 07:22:51 am »

It turns out that with a red LED torch, the emitted spectrum is so narrow that the best that can be done is to make in a B&W photo.

Red cellophane (or plastic) appears to have a much broader spectrum!
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rdonson

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Re: Is it possible to go below 2800K?
« Reply #5 on: October 01, 2016, 10:38:45 am »

Did you try shooting a gray card and creating a custom white balance in camera?
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Ron

sniper

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Re: Is it possible to go below 2800K?
« Reply #6 on: October 02, 2016, 10:16:00 am »

I don't think a custom WB will help, the problem as other have stated is red leds more or less only give out red light, there simply isnt enough of the other colours to ballance it out, a better bet might be to work in black and white, that was a popular solution to shooting under the old sodium lights of years ago with film (which had a similar problem)
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Jack Hogan

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Re: Is it possible to go below 2800K?
« Reply #7 on: October 02, 2016, 11:53:25 am »

Recently I purchased a red LED flashlight to do some night time shooting of animals without disturbing them with the light. Unfortunately it turns out that the red light from the LED flashlight is too red for LR (or ACR) to be able to handle. If I move the white balance down to 2800K, I still have a predominately red image. This is in contrast to using (say) red cellophane in front of a normal torch which has a correctable temperature.

I suppose there are a couple of questions here, such as..
- is it possible to go below 2800K with other raw processing tools?
- why does ACR/LR set 2800K as the minimum?

Have you tried using a gray card and sample white balance off it?

Jack
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