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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 -- 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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