markarian's chain

[alacant]

Hi everyone. Non-elliptical galaxies -almost. I followed Markarian's Chain -close on 2 hours- up to the meridian. Still getting the ligh-tish strip along one edge. I think my next project will be to perfect gimp's dodge tool... Thanks for looking, clear skies and as always, suggestions for improvement most gratefully received. TIA.

[PeterCPC]

I like that but it's a bit too green I think.

Peter

[geordie85]

Nice image. I love this patch of sky, so many galaxies. It gives me a real sense of the enormity of our universe.

[alacant]

55 minutes ago, PeterCPC said:

too green

Ahhgghh, the colour. I'm hopeless at that. Could anyone do me a big favour and have a go? Here's the histogram. TIA.

 

[geordie85]

I saved your jpeg and simply ran HSVG for Photoshop. Gets rid of green tint automatically

[PeterCPC]

Had a quick go in Paintshop - a bit better I think.

Peter

[Astrosurf]

Nice shot! Can you give us specs about the capture, equipment etc?

[alacant]

1 hour ago, Astrosurf said:

capture, equipment

Hi. NP. It's around 90 minutes of snaps with another 30 or so for dither and all the other stuff. Canon 700d. Thanks for looking. 

[ollypenrice]

Obviously there's a lot to like in this but the background isn't flat and that would be my big priority. There is a big bright patch starting in the middle of the lower edge and sending fingers of brightness outwards. Please forgive the teacher-ish green ink but this is the bit I'm talking about. I'm totally confident that the brightness is an artefact, having imaged this region extensively and never seen anything comparable.

Olly

[alacant]

49 minutes ago, ollypenrice said:

isn't flat

Yep. There's always something along one edge . Proper flat frames would probably help but does anyone have any ideas what it is caused by? The only way I've found effective is cropping 250 pixels from that edge. Here's aCR2 flat frame and the same frame stretched below. TIA.

[ollypenrice]

That does look like simple optical vignetting. A little assymetry isn't unusual.

Olly

[alacant]

3 hours ago, ollypenrice said:

optical vignetting

Is this a hardware problem or do you think flat frames will fix it, or something else? TIA. 

[ollypenrice]

Flats should deal with it. They really are very important in the imaging process. When you take them, open them in a programme which allows you to mouse over the flat so as to be given the brightness values in ADU. You'd expect the centre to be lightest and the corners darkest. A fall off as bad as 25% will be happily corrected when they are used. (I may have 23,000 in the centre and 19,000 in the corners, for instance.)

Olly

[Petergoodhew]

22 hours ago, ollypenrice said:

Please forgive the teacher-ish green ink but this is the bit I'm talking about.

Olly marks my homework the same way!

[Adam J]

I have asked the question before as to why this site does not have a monitor calibration page / image, with my PC screen the area that Olly has highlighted shows no visible gradient. Olly clearly has a higher contrast setting on his monitor than on mine. 

[alacant]

36 minutes ago, Adam J said:

no visible gradient

Apart from that awful white strip along the edge, I can't see the artefacts either and it doesn't show on any blog images I post. There is something there, but to see it clearly, I have to load it into gimp and up the brightness. I think it not only depends upon what you use to view the image -chrome, firefox, gimp, pi, ps, st0...- but also the ambient light around you as well as the hardware you're viewing on. As you say, too many variables over which we have no control. Yes. A gamma calibration greyscale and colour swatch would be helpful, especially for the imaging sections.

I'd still like to know how to get those flat frames right though so I could then start looking elsewhere in the process for a solution:)

TIA and clear skies

[glowingturnip]

do your darks have that bright strip too ?  Might be amp glow or some such in the camera if so

[alacant]

21 minutes ago, glowingturnip said:

your darks have that bright strip

Hi. I don't use dark frames as introduces too much noise, but as it's present on light and flat frames at all exposures and with all optical trains, maybe I can rule out the glow? Thanks.

[alacant]

Hi. Had a go with gimp's sponge but had to lose a galaxy along the bad edge. Still can't get the colour but the bg seems more under control. Still a way to...

Edit: On second thoughts, it's worse! Time to give up...