Generally speaking, the Moon has an albedo about that of black
coal. But it does have a surface littered with different mineral
structures and deposit and thus, much dependant uppon the the
incident angle of Sun rays, the Moon does show subtle variations
in colour across its surface. These colours are usually quenched
in the overall overwhelming glare of the Moon. Although the
albedo is like that of coal, the contrast to the surrounding sky
is too much for the human eye to discern the faint play of
colours which we see best - if at all - when the Moon is low in
the sky where Earth's atmosphere weakens the glare of the Moon.
But camera sensors have a different perception of light and
brightness so, could we use Hygh Dynamic Range (HDR) techniques to
bring forward colours on the Moon?
The anwer is yes - -
- sometimes - - - if you excersise great care and have a good
deal of luck too..........
HDR doesn't work too well in lunar photography because even the
tiniest blur due to less than perfect seeing and even the
smallest effects of field rotation will be magnified in HDR
images. Therefore, very good seeing and stacking of a number of
series of images with varying exposure times are prerequisites
to successful attempts at lunar HDR photograhy.
And then, they
are prerequisites but not guarantees. One can never decide that
tonight I will do some HDR photography of the Moon. One can only
decide that tonight I shall TRY to do that.
My successes are
limited so far. They can be counted on some three fingers, but
on the night between 20 and 21 March 2011, where the Moon was at
closest approach to Earth and everybody were pointing their
cameras at the Moon, I decided to try to get something different
to show. Thus, with a Meade LXD-75 equatorial mount, a Pentax
K200D DSLR, a
Tamron Adaptall-2 SP 300mm f/5.6 lens
(Model 54B) and an SP F-series 2X teleconverter i
took series of some 6-8 images at 1/125s, 1/250s and 1/400s at
ISO 500. These series were individually stacked in Registax, the
stacks then carefully aligned, cropped and merged as an HDR
image in PhotoImpact. It further took a good deal of work in
curves and levels and applying some
pseudo LRGB techique before
colours finally emerged.
Now, move your
cursor over the image (single exposure at 1/125s) to see the
effect of stacking and click on image to see the final outcome.
Do note, that no coulours have been added to or painted on this
image - only enhanced using
standard enhancement techniques.
One might argue that the HDR Moon is un-natural and not worth
the effort, but that is not an appropriate view. The goal is not
to produce a harshly coloured Moon but to bring forward that
subtle detail that can otherwise be so difficult to record,
especially on the Full Moon. What you see is rather like a
colour coded contour map of the Moon - only, the colours came
from the Moon itself!
And, finally, it was
simply great fun to make that image!!!