Imaged this on 30 August from Leyburn but the colour of NGC2070 looks too green and blue to me. I have attempted to colour correct with MaximDL 6, and CCDStack 2 a couple of times, but not successful. eg. I tried splitting the RGB frames, then re-combining with reduced Blue %, but it didnt look correct.
Is there something about OSC images that I'm missing here? Any clue and helpful comments welcome.
Looks pretty good! I imaged the SMC with a mono camera and a lot of the nebulosity was OIII heavy and bluish so I don't think you're too far off. It would probably be improved by subtracting a bit of green (SCNR in PixInsight, HLVG in Photoshop.) You could get the reds to pop by adding Ha, of course...
That's very cool Greg. The hires has some serious image scale. Very refined and detailed.
I don't think you'll get much red in the tarantula with a DSLR. Even with a CCD there's a big amount of greens and blues in it.
Hi Greg, even modded dslr's seem to show Tarantula as very blue-green, I suspect it has oodles of H-beta emission that overpowers the Ha. This is just a theory I've come up with to explain what I see, I've never been very successful in finding an official explanation.
Thanks Rick, Marc and Simon..I'll have a fiddle, but I suspect you're right, I wont make much progress. I find a lot more red when it is imaged with the QHY8L..I must post that image too, but it was taken thru the MN61 at 900mm.
Hi Greg, even modded dslr's seem to show Tarantula as very blue-green, I suspect it has oodles of H-beta emission that overpowers the Ha. This is just a theory I've come up with to explain what I see, I've never been very successful in finding an official explanation.
The ratio of H-a to H-b is pretty much fixed (1:2.85). Extinction from dust is apparently what causes the H-a to be lost ( http://en.wikipedia.org/wiki/Extinction_(astronomy) ), though I think there's a lot of OIII in this region too.
Thx for tips guys..
Hmmm, had a fiddle with PS, adjusted it so less green around the Ha of NGC2070..better rendition?
see here for full res http://www.astrobin.com/full/124847/B/
In PS, use Adjustments -> Hue/Saturation and select blue and/or cyan and fiddle til it looks right. I know with my FLI 8300 OSC with an LP filter, I have to manipulate the blues a LOT.
I also find with CCDStack for OSC that it is IMPERATIVE to debayer PRIOR to registering and stacking, otherwise you get a "tartan" OSC grid effect, or very distorted colouration. Also use the Colour adjust to change the background - I always desaturate the background. It helps balance the blues a bit more too.
Thx Lewis and Marc
yes, second version has been treated exactly as you outlined Lewis, as well as de-saturating the background in CCDStack. And yes, Mark, exactly right, i found this out by mistake quite a while ago. which makes sense when you think about it.
I think the second one is much better, and also matches the same area taken with the QHY8L through the MN61.
Actually great to read this - I've just got myself a 6" newtonian astrophoto rig, and one of my first targets was the tarantula (camera is an unmodded 60D). It came out just as blue-green as yours, and I worried about the reason . Even accepting the lower H-alpha sensitivity of the camera, it seemed a bit much, though I'd read about NGC 346 being more green than red , other nebulae have come out nicely red/pink in the 60D. A 1959 paper on the NGC 2070 spectrum notes a lot of OIII, but the spectrum in the paper didn't appear to cover H-alpha, so I couldn't make the comparison. But... it's reasonable that this nebula has a sizeable contribution of OIII.
which makes sense when you think about it.
