Using gray/white card to determine white balance, does it matter where I stand when I take reading photo?

Question

If I want to use a white card to determine the white balance, and I'm taking a picture of something that is a short distance away from me, does it matter if I don't walk back to where I'm going to stand when I take the final photo, when I take the photo for white balance?

Let me rephrase that.

Suppose I can walk up to the subject, place my white card on/against it. What if I don't bother walking all the way back to where I'm going to stand when I take my actual photo, when I take the photo I'm going to use for white balance.

Does it matter?

I understand that if I'm so close that I'm actively blocking or influencing light, then it matters, but if I can avoid that, I'm thinking this won't matter a bit.

I also assume that if I capture the image from a different angle than my final one, then it might matter, but again, if I can avoid that...

Am I right in my assumptions?

Answer 1

the only relevant thing is that the same light which falls on your main subject falls on your card. The field of view, distance and so on don't enter in the equation. but you have to be sure that by standing near the subject you don't influence in any way the light, which is not always easy since our eyes are very quick to adapt to variation and they interpret what they know to be of a given colour. So you can do that, but be always self conscious of your positioning. in any case small variations are not something to be worried about, since your subject is not a priori a small planar surface but is much larger than the card to start with. basically avoid to project your shadow or to "reflect" too much light onto the card and you'll be fine.