noob RAW color temperature questions

[Reef Bass]

I shoot under 20,000K MHs so maybe those of you with lower color temperature bulbs don't experience this to the same degree that I do. And probably my background in software development makes this issue more annoying for me than others.

In theory, setting the white balance in raw images can be as easy as entering the color temperature of your lights.

However, I notice that sometimes when I do that, the resulting colors do not appear as accurate as I would expect. Generally they are a bit yellow, or as though I were trying to set the color temperature too high.

Anyone else experience this? Do you just ignore the color temp value and adjust slider until the image looks right? I know one can use the eyedropper too but what if there isn't any white in the pic to use as a reference?

Also, I notice in the Camera Raw window when opening RAW images, the initial color temp value varies, usually between 5 and 7000K. What determines this initial value? Is there any significance to it?

The various sliders seem to be prepopulated with initial values. Are those determined by my camera's profile?

Thanks for your patience with my questions and for any insight you may be able to provide.

 

[Genetics]

Bulb temperature is not 100% correct. If the image is too yellow try a lower kelvin value to get the correct color. The initial color temperature is similar to that of outdoor sunlight.

 

[Reef Bass]

What I'm hearing is "ignore the value, use the slider". I guess what bothers me about that after using the slider to make the pic look reasonably color accurate, the value being used seems so far off my light's color temp that I feel I must be doing something wrong or have made a mistake or the software isn't working properly. For example, the image looks accurate at slider position 10kK and my lights are 20kK. I guess I just need to get over that?

I know older MH bulbs loose intensity, but do they also change color temp? Mine are only about 6 months old, so I don't think they've changed a whole lot yet.

Yes, I recognize the value range of the initial color temp as roughly that of sunlight. Just wondering why it's not constant. I mean, if the raw file contains unmanipulated image sensor data, why is the initial color temp variable? Probably a question for a Canon or Adobe user forum. Nevermind...

Thanks Genetics.

 

[BlueCorn]

Actually, the initial value that you see depends on the camera's setting. If you're set to "auto" the camera makes it's best guess and that's why you see the starting point change. Don't get too hung up on the actual value shown on the slider. Your goal is to make it look right.

 

[Reef Bass]

Thanks Doug. I seemed to need permission to ignore the value. I'm not trusting myself enough yet.

Your comment about auto mode makes sense. That's probably where I noticed the variability, particularly 'cuz I'm usually shooting in Av.

 

[TitusvileSurfer]

Av is a great chioce, but I think Doug meant "auto whitebalance". I don't think shooting in Av should matter one way or the other?

 

[Reef Bass]

Thanks for making that distinction TS. Having been shooting entirely in RAW, I haven't played with white balance settings on the camera. I just looked and it is indeed set at AWB.

It's like you guys know what you're talking about.

 

[BlueCorn]

 

[ogre1231]

You can try using a gray card as a reference. A whibal card work very well too. The gray card basically produces a constant color reflection that you can use photoshop to edit after the photo has been taken. The whibal card you use to set the custom white balance in your camera. Very easy to use and very useful.

 

[Reef Bass]

I tried several times to set a custom white balance using a white object inserted into my tank and while the procedure was straight forward, I still wasn't happy with color accuracy afterwards. I find shooting in RAW much easier as it eliminates the need for all that and the resuls are much better as white balance can be easily set in software.

I just noticed that was your first post! Congratulations and welcome.

 

[nickb]

If you take a photo of the white/18% gray card under your tank lighting, you can use that to set the WB adjustment for RAW processing.

 

[Slakker]

The way your eyes see 20k and the way the camera/computer see 20k will be different, so it's only safe to assume that the white balance correction wouldn't necessarily be an exact science.

 

[Reef Bass]

What? You mean there's not a real human eye in my camera evaluating the light and describing the image to the ram card??? I'm sending it back!

:lol:

Thanks for your suggestion nickb and your comment Slakker. I appreciate them and am enjoying the learning I am doing.

Ken