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ASTRO: Hercules Cluster ABELL 2151



 
 
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Old February 13th 08, 06:32 PM posted to alt.binaries.pictures.astro
Rick Johnson[_3_]
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Default ASTRO: Hercules Cluster ABELL 2151

I took this at the height of my filter wheel problem. In fact it was
the last thing I did before I discovered the problem. Later that night
the wheel really acted up to the point it was obvious, images were 40%
one filter 40% another with a center black band between filters. Still
the wheel was returning to seek errors as it should have and did after
my first repair tightened things too much. I guess a little error it
tells you about but one too big to fix it doesn't.

Anyway I had to throw away a lot of frames so this doesn't go as deep as
planned. No flats could be used as the wheel position can't be
duplicated. I've tried. Pseudo flats correct big problems but do
nothing for the myriad of dust donuts of all sizes. I spent many a
night dealing with them individually on the 15 frames I did clean up.
Still the treatment had to be severe and now if I get up about 4 a.m. I
can retake it. So why I went through all this I don't know. Probably
the clouds talked me into it. Since fixing the wheel I've had only 6
nights suitable for imaging in 6 months, all with a quarter moon or more
to deal with.

This cluster was one of my first deep attempts after getting the 14".
But only in black and white as I didn't have good color software -- or
black and white for that matter! Unfortunately I was using the Meade
electric focus unit that couldn't hold the camera without tilting under
its weight. Only the center column was usable making for a rather
square shot actually taller than wide when I cropped out the areas
ruined by the sag in the focuser. This was the shot that told me it had
to go. I'm sure it's fine with a light camera, just not something as
heavy as the STL line. Or with a big chip, it vignetted the STL-11000
chip rather severely. More than the flats could handle, partly because
the sag depended on where in the sky it was pointed so the vignetting
wasn't constant and never matched the flats unless you took them in the
same part of the sky as you imaged.

I thought of using the new color data with that old photo but found even
though the good portion of that image looked fine there was no way to
line up stars on the top with those on the bottom. The sag changed the
scale from the upper left being least to lower right the biggest scale.
The difference was about 4 pixels and very obvious. So this is all
new data. Until I retake it, this will have to do. I had to go light
on the color as otherwise the flat problem was really obvious. Still it
appears to be a rather weakly colored field.

14" LX200R @ F/10, L=6x10', RGB=3x10', STL-11000XM, Paramount ME

Rick
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Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

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