Sodium vapor light sources, either high-pressure or low-pressure, are not continuous spectrum. No amount of simple filtering will allow color matching, unless you employ a custom color notching dichroic filter. Even with the custom dichroic filter on the flash, accurate color balance will be difficult to impossible.

Worst-case scenario is this type of sodium vapor bulb:


(Image attributed to "Gebruiker:Gerben49" of the Netherlands.)

Yes, I've shot under that kind of light and yes, I converted to gray scale. Not much else you can do.

Under some circumstances, like for formal group pictures, you can use multiple flash and HSS/FP mode for flash and camera, and set a very high shutter speed to try to reduce the ambient light as much as possible. That approach probably would not be appreciated during a game, however.

Originally Posted by ziggy53 Sodium vapor light sources, either high-pressure or low-pressure, are not continuous spectrum. No amount of simple filtering will allow color matching, unless you employ a custom color notching dichroic filter. Even with the custom dichroic filter on the flash, accurate color balance will be difficult to impossible.

I think that's what they are. So yeah, your suggestion is pretty much all that one can do - either white balance for ambient and, in case of action, run a high iso; or drop ambeint so it's suppressed by two-three stops and run with flash.

Thanks.

How I choose a gel.

I set the camera to auto white balance and shoot a piece of white card stock that fills the frame. Be sure to expose to the right. That is, on the histogram be sure the data falls to the right(white) and not somewhere in the middle. This frame can be used as the recerence frame for a custom white balance. Swith to custom white balance. Also chimp that cwb reference shot. On the lcd does it appear orange? Yellow? Green? Lay the card stock on a table and drop a few gels onto it that approximate the hue seen on the reference shot. Try to match it. My best match is usually by using the next denser colored gel than the one that matches.

You may have to mix two colors to get a match in a gym.

Originally Posted by jeffreaux2 How I choose a gel. I set the camera to auto white balance and shoot a piece of white card stock that fills the frame. Be sure to expose to the right. That is, on the histogram be sure the data falls to the right(white) and not somewhere in the middle. This frame can be used as the recerence frame for a custom white balance. Swith to custom white balance. Also chimp that cwb reference shot. On the lcd does it appear orange? Yellow? Green? Lay the card stock on a table and drop a few gels onto it that approximate the hue seen on the reference shot. Try to match it. My best match is usually by using the next denser colored gel than the one that matches. You may have to mix two colors to get a match in a gym.

OK .. something's not taking root in my brain here. If I shoot AWB on a frame-filled white object, won't the resulting picture appear white under AWB?

What I'm not understanding, here, is where the colour cast for matching the gels would enter into the equation...

Originally Posted by Moving Pictures OK .. something's not taking root in my brain here. If I shoot AWB on a frame-filled white object, won't the resulting picture appear white under AWB? What I'm not understanding, here, is where the colour cast for matching the gels would enter into the equation...

If I follow the procedure to capture a reference frame for white balance per Canon's book ( I believe it says use AWB?) then the resulting frame will have a cast.

For Canon custom WB, at least on the 7D and as I remember it the on the 10D, it doesn't matter what white balance you choose when you shoot the test frame, custom white balance works off of the raw image. After you shoot the test image, you go to the menus (not on the LCD on top) and select custom white balance. It asks which image to base the while balance on. If it it thinks the image it good enough it will as you to press OK on the screen.

Then to use that custom white balance setting you select custom white balance on the LCD on the top of the camera.

As Ziggy mentioned if there are two different color light sources illuminating the image, you still may end up with a color cast in the jpeg but you should be close.

Originally Posted by Dan7312 For Canon custom WB, at least on the 7D and as I remember it the on the 10D, it doesn't matter what white balance you choose when you shoot the test frame, custom white balance works off of the raw image.

Yep. So when I shot white at the gym the other day (a chunk o blank paper), it was yellow under a flourescent white balance.

The previous suggestion was to use AWB, tho, and I'd figure that if you park AWB on a white object, it should come up ... white.

I'll go check it out sometime, see what happens.

The method I use is fairly solid.

Much better than guessing.