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Penguin

What's going on with my stacking???

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So over the weekend I had a few goes at imaging objects in the Virgo Cluster, and I can't get anything good out of the results. This is using an unmodified EOS450D through a SkyWatcher 150P on an NEQ5-Pro without guiding. There seem to be two main problems.

1. After stacking in DSS, the resulting image has obvious horizontal banding. I use Darks and Flats taken on the night, with Bias frames that I took a few months ago. I tried stacking with none of these calibration frames and the stack came out much better (with regard to the banding anyway.

2. When I pull these into PixInsight, crop them and then do a DBE with settings I have been advised to use on here and that have worked nicely in the past, they don't do anywhere near as good a job: the extracted background is solid red (I am not used to my initial stacked images being this red either) and the only improvement to the image is the lack of that redness.

I have attached examples of the dark, flat and light frames, along with the final stacks (with and without the calibration frames) and a screenshot from PixInsight showing the full horror that I am trying to work with. Any advice would be hugely appreciated.

--- Alistair.

 

D_0155_ISO1600_120s__20C.CR2

F_0199_ISO100_1-5s__18C.CR2

L_0182_ISO1600_120s__20C.CR2

stacked-with-calibration.TIF

stacked-no-callibration.TIF

PixInsight 1.8 screenshot.png

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I'm curious to know if it is just a typo or if you actually shot your flats at ISO 100 and your lights with ISO 1600.

I had a little play in Photoshop with your data (stacked and calibrated TIF) that you uploaded and I got this. As you say there is a lot of banding and red noise in the image and you have some star trailing.

What are the details of your subs? Sub length, ISO etc.

stacked-with-calibration.jpg

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The ISO and sub lengths are as in the example shots, it's no typo. Again on this forum, I have been told that the ISO for flats does not need to match the other frames since their purpose is the removal of dust bunnies etc and the measurement of vignetting and other effects of the optics rather than anything to do with the sensor. So I have gone to ISO 100 since that evens out the flat field: the LED lighting panel I am using to generate my flats refreshes at something like 50 or 60Hz (mains frequency?) so I need to expose for significantly longer than that to get an even flat image and the easiest way to do that is by lowering the ISO. However, maybe my flats are causing some of these problems?

I will have another look at stacking in PixInsight, I have got used to DSS, where I pretty much just accept the suggestions that it offers. PI seems to demand a bit more knowledge of what is actually happening, which can only be a good thing in the long run!

Thanks for the help thus far.

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I spent several hours running through the stunning lighvortex preprocessing tutorial. Unfortunately, I realise now that I should have adjusted the numbers in the weighting expression, and also, because I had not yet upgraded to 1.8.5, could not use the 'local normalisation' section. Anyway, the result is shown below and is still full of noise and banding, both of which I think must be the result various issues at the scope. I think I need to re-check my alignment and gather new data, rather than continue with this image.

 

pixinsight 1.8.5 screenshot.png

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Hi. The flat frames haven't done as good a job as they could. Maybe the camera had rotated after you took the light frames? Just a guess.

GIMP 2.10: the stack has a nice glow to it. Nice galaxies:)

v.thumb.jpg.d7b9665b21fc1e22ca7b4f10a23ea356.jpg

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I think something like that must have happened. I never move anything between taking lights and flats but maybe the camera got knocked slightly. Thanks for playing with it.

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