by Crestie Crazy
, on Flickr
Random sky around Ursa Major or big dipper. Looks like I just missed M101 so I'll have a go at that tonight, weather allowing.
Canon 450D filter moved, Zeiss 50mm makro planar at f/2, >850nm IR filter. Astrotrac. 5x4 minute exposures.
Pixel peeping, I'm seeing what appears to be astigmatism or coma towards the corners. Previously I have tested this in visible light and it was well corrected. I guess working in the IR region is pushing the lens outside its comfort zone.
Above is the same shot, but with the levels right up. Interesting I notice there's some concentric rings visible. Wonder what that is, either an optical effect or perhaps a side effect of PixInsight's DBE function. I also notice there's a very faint trail that escaped the processing, and the dust spot to the left that's been annyoing me ever since I had the camera initially converted. I really need to clean that but hadn't previously as it was trapped under the filter, but now I removed the filter I can only blame my laziness that's still there.
And finally, I also had some weirdness I've never seen before and am at a loss to explain.
This is a straight converted output of a different part of the sky. Instead of the even glow of background noise, what is happening there? I did wonder if the bright region near the bottom/left was some really weird kind of lens flare, but that wouldn't explain the dark regions at the bottom. I saw this effect in two different parts of the sky so I'm not sure it's an external issue (not clouds or anything like that), but something to do with the kit. Camera seems to work fine otherwise.