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 Post subject: Follow the bear...
PostPosted: Sat May 12, 2012 8:25 am 
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Posts: 8022
Location: UK
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Bear's tail 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.

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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.

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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.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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 Post subject: Re: Follow the bear...
PostPosted: Sat May 12, 2012 10:11 am 
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Hi popo,

Could they be very faint noctilucent clouds distorted by the camera's tracking? I didn't see any from last night's results but I was imaging near the zenith until midnight and then switched over to the north east horizon until moonrise so I wasn't really looking in the best place. I used to see them most often in the east shortly before dawn when flying back from the States but if they are around they should also show after sunset in the west.

Off-topic but did you get anything useful out of that freezer experiment?

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: Follow the bear...
PostPosted: Sat May 12, 2012 10:48 am 
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Joined: Sun May 25, 2008 12:48 pm
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Location: UK
I saw this effect one two occasions, one in the general vicinity of Virgo as pictured, and later in the night around Arcturus. The pattern is practically the same hence I don't think it's cloud.

My shooting sequence was something like:
30s Virgo, normal
3x2m Virgo, normal
3x4m Virgo, weird
30s Plough, weird
7x4m Plough, normal (how did I miss two for the earlier stack?)
90s Plough, normal
3x4m Arcturus, weird

Given one of the Plough shots was weird I think rules out cloud or external factors. I did wonder if it could be flare, but again that seems less likely now. Maybe the camera is playing up?

On the freezer experiment, yes the cooled camera gave less noise. On a 2 minute exposure, I'd rate the advantage as less than a stop worth of noise brightness, bearing in mind of course the sensor would be heating up during those two minutes. Didn't measure it more scientifically beyond that. The normal temp noise was quite uniform. The chilled noise had banding, which I guess could be present but masked at normal temps.

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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