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Author Topic: Catalina and m101 on Friday night  (Read 1052 times)

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Offline Dave.M

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Catalina and m101 on Friday night
« on: 14:44:40, 19 January, 2016 »
Unfortunately it was cloudy on Saturday despite the forecast so this is the closest I got.
William Optics 71ED and canon 1100d camera.  8x180 secs at iso 1600 + darks and flats. Still getting stray light in somewhere though. :no:

Offline Roger B

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Re: Catalina and m101 on Friday night
« Reply #1 on: 16:51:32, 21 January, 2016 »
The stray light could be though the view finder

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Offline Dave.M

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Re: Catalina and m101 on Friday night
« Reply #2 on: 17:06:19, 21 January, 2016 »
No got that covered!

Offline Darkstarshado

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Re: Catalina and m101 on Friday night
« Reply #3 on: 19:53:21, 21 January, 2016 »
Could a combination of a LP gradient and bad flats.  What does the stack look like without the flats?
If you use DSS, be aware that the histogram curve of each of the 3 colours in the flats needs to be (ideally) near the middle and certainly not cropped at the left or right as DSS corrects each colour separately, using the corresponding colour in the flat.  Took me a while to get that right when using a LP filter!
Just my tuppence worth and something worth checking.   ;)
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Offline Einari

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Re: Catalina and m101 on Friday night
« Reply #4 on: 20:16:45, 21 January, 2016 »
Could be LP indeed.
Btw, you use bias with your flats ?
And, must add that GradientXterminator could help here.
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Offline Dave.M

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Re: Catalina and m101 on Friday night
« Reply #5 on: 14:53:09, 22 January, 2016 »
Thanks for the comments. The individual frames all show he same effects. Must admit I don't use bias frames.  Do use a lp filter although not on these ones. Always need to change the colour balance with this. Can't understand why I get it with both scopes (refractor and reflector)  and both cameras 1100d & 60Da.

Offline Einari

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Re: Catalina and m101 on Friday night
« Reply #6 on: 17:04:07, 22 January, 2016 »
Then it's LP. Use LP filter and take bias frames and processing is easier.
Tapio

Celestron C8, C9.25" & Hyperstar, iOptron CEM60-EC, TS 80 triplet,  Coronado PST, SXV-694,  ASI120MM/ASI174MC Cool

Offline chris.bailey

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Re: Catalina and m101 on Friday night
« Reply #7 on: 17:29:02, 22 January, 2016 »
If you use flats you need to use Bias And/Or Flat Darks or the math doesn't work - (Light-Bias or Dark)/Flat-Bias or Flat Dark)

Being simple for single pixel if Signal=1,000, Flat=400 and Bias=100 Bias subtracting the Signal and Flat to get true values gives 1,000/400=2.5 which is different to (1,000+100)/(400+100)=2.2 i.e. the uncalibrated Signal and Flat both include Bias. The difference between the results will vary according to the level of the signal so the flats will not work correctly. For a cooled CCD short duration Flat, Dark signal is negligible but on Kodak CCD's, if the Flat is anything but a few seconds (Ha filter) then you should really do Flat Darks (i.e. Darks of the same duration as the Flats).
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Offline Dave.M

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Re: Catalina and m101 on Friday night
« Reply #8 on: 18:34:18, 22 January, 2016 »
Thanks. Will give it a go.

 

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