Custom White Balance

Was wondering if someone could help me with this...

I often set a custom white balance with the help of a white/gray card. My question is, if I change the shutter speed, ISO, or aperature, do I need to create a new custom white balance? I'm suspecting that I do since the ambient/flash mixture will change.

A similar question is if I change the distance from camera to subject, do I need to create a new custom white balance?

Thanks for your response.

While white balance can affect exposure, unless you are allowing in mixed lighting sources with drastically different camera settings, you shouldnt need to reset a custom WB. What I mean is, if you have settings of 1/200th, iso100 and F9 which completely kills the strong tungsten light and then switch to 1/60th, iso 1600 and F2.8, youll now have mixed lighting (all of this assuming your using strobes).

If you are using solely ambient light, then no, adjusting your WB isnt needed.

Also, for number two, same answer, no need to reset it.

If there is only a single source of light, you never have to readjust even if that light changes brightness.
If there are multiple sources of light, if they are all constant sources and the subject position relative to Source A vs Source B changes, then you will need to adjust WB if you truly care about accuracy of color rendition. Often, for snapshooting purposes, the brain is forgiving enough to well tolerate minor changes in WB.
If there are multiple sources of light, if there are a mix of some are intermittent sources and constant sources, you would adjust to the most dominant source (e.g. if flash is more powerful than tungsten source, you balance to flash). Often, for snapshooting purposes, the brain is forgiving enough to well tolerate minor changes caused by the less dominant source.

Wilt wrote in post #13697746
If there is only a single source of light, you never have to readjust even if that light changes brightness.

If you're referring to changing the camera's exposure settings, I agree.

But actual changes in the brighness of most light sources are accompanied by a change in color temperature. Certainly tungsten lights change when they are dimmed. Many (most?) strobes and flash units will change color temp somewhat when you adjust the power. Even sunlight on a clear day changes color temp from dawn to mid-day to dusk. And certainly if a cloud moves in, the color temp will change.

In fact, about the only way to change the brightness of a light source without changing its color temp is to move it closer or further away.

Thanks guys! Appreciate the expert adivce!

Curtis N wrote in post #13698100
If you're referring to changing the camera's exposure settings, I agree.

But actual changes in the brighness of most light sources are accompanied by a change in color temperature. Certainly tungsten lights change when they are dimmed. Many (most?) strobes and flash units will change color temp somewhat when you adjust the power. Even sunlight on a clear day changes color temp from dawn to mid-day to dusk. And certainly if a cloud moves in, the color temp will change.

In fact, about the only way to change the brightness of a light source without changing its color temp is to move it closer or further away.

Curtis,
I don't know about your experience, but I seldom am in a situation where dimmers are used while we/the client is present, although I am not saying it doesn't happen. Certainly some tungsten lights can be turned off completely, which effectively reduces the light but with no effect on WB.
Tungsten dimmed will certainly change WB, most CFLs cannot be dimmed, and the sun is 'dimmed' by clouds and we all know how that cools the WB value.

John E wrote in post #13697307
I'm suspecting that I do since the ambient/flash mixture will change.

This is a really problematic area for me; I got into a situation like that a few weeks ago and it was awful: I had no gels for the flash and every shot had a different balance of the two lights, which were nowhere close to each other.

However, the problems go beyond just getting the best WB for each shot. Depending on the light placement, you will have different WBs within the shot and you can't fix that with any WB adjustment. You need to fix the light, either by gelling the flashes to better match the ambient or placing them so that they contribute more evenly to the scene.