Have you ever been to a home improvement store and seen a display that compares the color tint of different light bulbs (incandescent, fluorescent, halogen, etc.)? The world is filled with different "colors" of light. Light color can change from sunny days, overcast days, sunrise/sunset, shade, different indoor bulbs, and more. The human eye readily adjusts to the different lights so they all look pretty much neutral to us even though they are different colors. Most cameras are set to a default setting called Auto White Balance (AWB) which tries to adjust to neutralize the different lights just like the human eye does.
I always have my camera set to AWB and for the most part it does pretty well. I do make minor adjustments in Adobe Camera Raw or in Lightroom to get the white balance exactly right, which does end up taking quite a bit of time considering how many pictures I edit. I've been looking for something that would help me get the white balance exactly right in-camera so I could save time and hassle on my editing.
I was excited when I read about the ExpoDisc white balance filter... It seemed to be just what I was looking for! It's a filter that you place over the lens and you take a picture of the light that's falling on your subject (you basically stand where you subject will stand and shoot towards where you would be standing). Then you use that image to set the Custom White Balance setting on your DSLR. There are two versions: the neutral filter and the portrait filter, which has a warmer tone.
I recently purchased the portrait (warming) filter and used it for the first time today.
First I tried it in the shade. As you can see, the white balance of the first image (taken on AWB) is close, but not quite right. But in my opinion, the second photo (taken with the Custon White Balance from the ExpoDisc) is too warm.
Then I tried it with late evening backlight, which is my most common lighting scenario when shooting a photo session. The AWB image is too cool, but again, the ExpoDisc image is too warm.
I should mention that my daughter can be a tricky subject when it comes to white balance because her skin is SO white. It's hard not to make her look ghostly, but warming up her tones too much just looks wrong.
I think the concept of the ExpoDisc is great and now I really want to try the neutral one! I'll let you know what I find out ;)