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Re: [OM] I blew my moon shot

Subject: Re: [OM] I blew my moon shot
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 24 Mar 2011 10:13:11 -0500
For digital photography, getting a proper exposure of the moon is really
dirt easy:

Use the flashing highlights function in the image review. If moon is not
flashing, adjust exposure brighter and try again. Once you have a flashing
moon, adjust the exposure downward and try again until the moon no longer
flashes. There you go. Any brighter and you lose the texture of the moon
surface. Any lower and you lose non-lunar detail.

With film photography, it is highly recommended to spot meter the moon
itself. Adjust exposure so it is about two stops above middle exposure. Or
with the OM-3 or OM-4 series cameras press the highlight button. Doesn't get
any easier than that!

One caution about digital photography and photographing the moon. When the
moon is still low on the horizon the color will skew warm. The problem is
probably more specific to Olympus and Panasonic cameras, but the yellows
will clip even though you think you have headroom. They trick is to
expose-to-the-right, minus one stop. DO NOT go closer than one-stop to
clipping. You need that headroom! That's why the flahing highlights minus
one stop work. The flashing highlights actually kick in within that last
stop of latitude, so you'll actually end up with a bit more margin than if
you went specifically on the scientific numbers.

Again, this is very specific to Olympus and Panasonic digital cameras
because of the way the two green pixels are processed during the merge.
PanyOlympus uses four pixels to determine the RGB value, whereas nearly all
other cameras use only three. Where they calculate value at the junction of
a single green, single blue and single red sensor, PanyOlympus uses the
junction of four neighboring pixels. Normally, this is no big deal (other
than the loss of resolution inherent in four vs three pixels for each
resulting pixel location), but the way the merge occurs, there is a loss of
headroom in the yellows. Yellows and oranges will clip. It is a mistaken
belief that because there are 2X the green pixels on the sensor that all
cameras use 2 green, 1 blue and 1 red pixel in the algorithm to determine a
single pixel. That is really only true with Olympus, Panasonic and some
Kodak sensored cameras. Nearly ALL other cameras use one 1 green, 1 blue and
1 red pixel. It's an intersection thing. If you roll your own conversion
with DCRAW, you can override this and create your own method if you choose.

AG
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