jalafata wrote:
1. Is this just set up once, or several times with differing lighting situations?
2. Do I use a grey card, or will 97% reflectance photo paper work?
Any advice please? Thanks!
When you make a CWB reference shot you "measure" the color of the ambient light by capturing a frame of a subject with neutral reflective properties (i.e. something white or grey) that's lit by that ambient light. That measurement of the color of the ambient light is, of course, only relevant to shots taken in that ambient light. For instance, the WB "stuff" inside the camera sees a CWB reference frame with a yellow tint, figures that this is a yellowish light (e.g. tungsten), and then subtracts out that amount of yellow from shots that use this reference.
Get a grey card, they're cheap. If you don't have a grey card handy, try using a sheet of white paper, but do note that different types of white paper do have slightly different tints. Some people use the same photo paper they plan to use to print on in their inkjet. It's the "whiteness" of the paper, i.e. the neutrality of it, that's important, not how reflective it is. Grey paper is just white paper with lower reflectivity. As far as CWB is concerned, a grey card looks like a white card in dimmer lighting, assuming they're both equally neutral.
-harry