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The test phase
of the Hutech XTi is over, and some real astro imaging can begin!
We start with this set of images, taken this week from our mag
4 - 6 skies (depending on direction) here in Payson. I was very
curious as to whether the Halpha Pass Filter would perform with
todays glow from high pressure sodium lamps. Careful processing
of the 70 minutes of RGB data yielded a fine constellation shot,
with some red but little blue nebulosity. (Because the sky fog
subtracted it) When combined with 60 minutes of the red data
from the filter, the results were more representative of a dark
sky shot.
Image Description:
This image encompasses
the most spectacular portion of the Winter Milkyway. On the bottom
is the constellation of Orion, brimming with red hydrogen nebulosity.
The large "C" shaped arc is Barnards Loop, and above
it a huge red circular nebula known as the "Lambda Orionis
Nebula". Inside Barnards Loop is the three belt stars and
the "Zeta Orionis" nebulosity complex, which contains
the Horsehead Nebula. Of VERY special note is the red
strip of nebulosity on the far right edge of the image, going
up and down. This nebula, in Eridanus I had never photographed
until now. It is the right side of Barnards Loop that has been
blown off by the fierce stellar winds of the belt stars region.
To the left of Orion
along the edge is the bright small nebula the "Rosette Nebula".
Just above it is the "S Monoceros" nebulosity complex,
which includes "Hubbles Variable Nebula"
Two regions of nebulosity
are along the upper half of the image. On the upper right of
the frame is the huge "California Nebula" in Perseus.
Just below it is the brilliant star cluster the " Seven
Sisters" or "Pleiades". On the upper left is a
region of red nebulous patches inside the constellation of Auriga.
This includes IC405 and hordes of star clusters.
A snaking and branching
chain of dark nebula flow down from the top center of the frame,
and engulf the Lambda Orionis nebula. Most of these have Barnard
number designations.
Image Processing:
Once such a strong light
pollution gradient is removed from an image, the star magnitude
limits across the frame varies considerably. In regions of high
light pollution, there are few stars. To correct for this, I
used gradient contrast masks in Photoshop. You create an adjustment
layer in Photoshop for Levels. Then using the gradient tool,
create a gradient from black to white on the adjustment layer
mask, so that the white is over the areas of diminished stars
and the black over the darker skies areas. You then increase
the contrast of the frame by bringing in the top and bottom sliders
in the Levels control. This when combined with the mask brings
up the stars and contrast more in the diminished areas, and evens
out the entire image to appear like a shot from a dark sky site.
The red light shot,
with the Lumicon filter was added to the RGB image by splitting
the image into separate channels, and combining the red light
data onto the R channel with Screen at 100%, and to the B channel
at 10%. Backgrounds were readjusted to original values and the
three channels were then recombined for the final image.
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