[PhotosbyChuck]

Originally Posted by r_fredrick_smith

The only difference I can see in your example is difference is brightness.

Then you're missing the fact that the outer bands have significantly (roughly 5%) more red in them than the inner bands. Sample your own RAWs processed with the same color temps to be sure. All I had were the JPGs you posted.

Originally Posted by r_fredrick_smith

It does not change the fact that anyone using a good gray card for their CWB reference shot will get good color balance that is highly usable.

I said as much above. We don't disagree. "Good" is relative. Is a +/- 5% variance in red and a +/- 3% variance in green good? For most things.

Originally Posted by r_fredrick_smith

I really never said anything about reflectance and CWB as far as I can recall.

Originally Posted by r_fredrick_smith

But on another note, when I tested the Expodisc I found that I got almost identical CWB settings as when using the gray card. So that should suggest that reflectance is not the real issue (in most cases) --- the Expodisc does not depend on reflectance from a card (as you know).

Ah...I see part of why you're not following the reflectance comment. I just mean the light bouncing off of the card to be metered by the camera. It's called 18% because 18% of the visible light hitting the target is reflected. Back in the film days, someone figured out that 18% reflectance was the midpoint between white and black. To get the most of the film's lattitude, exposure could be set to a surface with a neutral 18% reflectance.

Ever use grass for this..it works pretty darn well for exposure -- about as well as a grey card. Just don't try it for CWB! So for the card to be "18%" it has a reflectance value of 18%. For it to be grey, the light across the spectrum must be reflected at exactly the same 18% without any variance. This is what I mean when I say that the card's reflectance value is for exposure settings rather than color balance.

Originally Posted by r_fredrick_smith

So to be honest, I'm still not sure I understand what point you're making. When I look at what you said here:

The first sentence doesn't seem to refer to anything that I said. From the way I read your statement your are talking about several different gray cards. I've never heard of a warm or cool gray card. You can have a warm card that is a shade of cyan, or blue or green and you can use these to get different results that could take middle gray as a starting point. All gray cards (if they are really gray cards) are by definition neither warm or cool --- they are neutral (equal values of RGB). So do you see where my confusion over your remarks stems? Are you saying something else, and I'm just missing it.

Here's an interesting test (I'd do it myself, but I just have 1 grey target):

1) Set your Macbeth card on top of the Photovision target. So we can see both "18% grays" very close to each other.
2) Meter the scene and then shoot 3 photos, changing only CWB
2a) CWB using the Macbeth 18% area
2b) CWB using the Photogivion 18% area
2c) CWB using the Expodisc
3) Process the RAW images without further adjustment other than the CWB

Sample the greys in all photos. Does the average RGB sampling of the Macbeth 18% gray target match that of the Photovision? They are likely to be a bit different. If they are, they're not really both grey -- and then you already own a warmer or cooler "grey" card -- you just didn't know it.

Note: I switched to grey for this post. I think I like it better!