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Originally Posted by Itchy
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OK. It's just that when I did my helix with my 300D, that colour turned out much bluer than yours: (I think you are right about the red noise)
http://users.bigpond.net.au/itchysas...30finalweb.jpg
Yes, "subframes" refer to your original individual exposures.
I use ImagePlus to do the basic processing. I shoot in RAW and convert to pre bayer CFA (Colour Filter Array). IP does the calibration (darks, flats and bias) including an auto matched dark. I then covert the CFA frames to colour before I align and stack. IP gives a range of stacking options. With a large number of subframes the sigma average seems to work really well. Once stacked I use IP's digital development process to do the initial stretch and then move to Photoshop to do the levels & curves, etc.
One thing that I have noticed is that ImagesPlus seems to enhance the blue in an image a little more that my manual attempts, so perhaps that is a factor in my centre of the helix being so blue.
Cheers |
Geeday Itchy,
First may I say that is a great image you have of the Helix, really shows the outer nebula well.
Might I also say, that everything else I say might be totally wrong! :-) I'm just a guy who enjoys astronomy and producing images to show other people - so what I say here, is just my humble thoughts.
I think the green colour is lacking in your image because your individual exposures are too short to detect that colour. meaning; there are too few "green photons" to collect in that short exposure time.
My exposures are individually longer (which gives an improved signal to noise ratio than shorter images) and also bear in mind my 'scope collects around 40% more light than yours and at 1/f-stop faster (I think). These factors attribute to collecting a lot more of those green channel photons.
Finally, I will say that most of my raw images also are "too blue" when I first stack them. But I work on the basis that the EOS produces images which have too much blue and therefore you must either add one colour or increase two colours to balance the colour. But this also depends on the amount of sky pollution for that night since pollutions tends to produce more yellow(brown) glows on my images, so the colour handling is slightly different.
BTW: I'm not sure what CFAs or Sigma Averages are.
something to do with the auto-stacking software?
PS. Last night I managed 40 minute exposure of NGC300 after that major storm we had (near Newcastle), then it started to cloud in again.
Regards
Paul