When I have to do a custom white balance, which of course is only when
shooting jpegs, I just use the grey card or a white card for that
matter. If I don't like the results, I use the -3 +3 adjustments. It
doesn't really mater what the Kelvin temp might be if the shots look
good. The only time I shoot jpegs is for virtual tours. But many of
these involve complex lighting: windows, tungsten, sometimes even some
fluorescent. But the data is irrelevant. Only the results matter.
Paul
On May 9, 2009, at 8:13 PM, Matthew Miller wrote:
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 [email protected] <http://mattdm.org/
>
The Definitive Pentax P-TTL Flash Model Guide: <http://pttl.mattdm.org/
>
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