On Fri, May 08, 2009 at 10:14:51AM -0400, Doug Brewer wrote: >> G-M means "Green - Magenta". The other one is "Blue - Amber". When you set >> manual white balance, you choose a Kelvin value, and then can set both of >> these two axes between -3 and +3. (The same adjustment grid that you use to >> tweak the pre-set white balance.) The question is: -3 to +3 *what*? > now, see, I had considered that this might have been the case, then tried > to over-complicate it.
:) > I guess the way to figure "-3 to +3 what?" would be to establish the zero > point (what is the Kelvin value of zero in this instance?) then look to see > what the Kelvin values are at +1, -1, etc, and the interval would establish > what they (Pentax) consider the units. > Make sense? Yeah, it makes sense, but for two things. First, the kelvin value displayed doesn't actually change -- the G-M/B-A grid is over to the right of that value and appears completely independent. And that's the second thing: the Kelvin scale measures along a blue-red axis. The green-magenta axis isn't related to that, so it makes sense that the Kelvin values aren't changed by it. But the blue-amber axis, by virtue of including blue, seems like it must have a complicated relationship with the Kelvin number. And I guess that's the third thing: it's hard to measure the actual impact of changes here. I suppose the test is to shoot a gray card with the custom white balance set to the card itself, and then see what divergence I get by changing the scale on *that* screen around. But even then, that's only part of the puzzle, and it seems like it should be the *harder* part, when I haven't even solved the easier part. Namely, once one has set the white balance with the gray card, there's no way to get a display of what Kelvin value that represents -- let alone the other offsets. I could buy an expensive color meter, of course, but that seems really weird to have to do when the camera clearly has one _built in_. Why can't it just display its readings? -- Matthew Miller mat...@mattdm.org <http://mattdm.org/> The Definitive Pentax P-TTL Flash Model Guide: <http://pttl.mattdm.org/> -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
