Rosette in HaRGB

[cfpendock]

Last night we had a couple of hours without clouds and not too much wind, so despite appalling visibility, like many other people, it seemed a good idea to try for the Rosette.  I managed to get 4 x 5 minutes each of RGB for the Rosette which I have now added to my previously acquired 6 x 20 minutes of 7nm Ha. When we get some decent weather I will try for more subs.   Atik 4000 and 4" refractor.  

 

It is a bit pink, and there is some slight vignetting - I have a problem with getting good flats and this was an experiment using less light and longer exposures.  Also a slight gradient?  I have heard of "Gradient Exterminator" - does this work without losing faint detail? 

 

The image also seems a bit bright in the middle, but I couldn't get rid of this without losing some of the faint stuff round the edges.  It seems this target has an enormous range of brightness.

 

The RGB in this image was not binned - I think it is better for it, and there is no luminance.  Most of the nebulosity detail is from the Ha, which was blended with the red.  Would it be better with some luminance, or is it not so important when the RGB is unbinned and there is plenty of Ha?

 

Criticisms, specially advice on gradient exterminator and making the image less pink would be very welcome.

 

Chris 

 

[PhotoGav]

That looks great, the detail is so clear and sharp.

You mention a few issues that you have with this capture / process; flats, gradients, pink colour & bright centre. I am very far from an expert, but will attempt a few comments, hopefully helpful!

Flats - how do you go about acquiring flats and what is wrong with them?

Gradient - download GradientXTerminator and give it a go in Photoshop. There is a free trial period, so see if you like the results.

Pink - I don't know the answer to this, but I have seen a couple of tutorials about this that might work. Here's one : http://starizona.com/acb/ccd/software/ps_hargb.aspx

Bright centre - it looks pretty darn good to me, so whatever you did worked! Photoshop curves and masks is the answer, which I reckon you have already!

Good luck!

[cfpendock]

Thanks for the reply, Gav. 

I tried various methods of getting flats - T-shirt, computer screen, blank wall etc.  The best seems to be the computer screen at around 20,000 ADU.  I cover the camera and computer when I do this to avoid stray light.  Sometimes the flats seem to over-correct in one corner and under-correct in another.  I use DSS for stacking, and I combine them with dark flats.  In this image I did have a problem, particularly with the red, which I had to tweak out with photoshop.  The camera is left on the scope and does not move between taking images and taking flats, which I should say are only for vignetting - the image train seems to be dust free.

Thanks for the info on gradient exterminator - I will definitely give that a try.

i have tried the Starizona methods of blending Ha, and I have to say that they don't help with the pink - I think all of these methods are very image dependent - some processing methods work well for some targets, others for others.

thanks for the comments

Chris

[PhotoGav]

Mmm, I might be at the limits of my knowledge now...!

I have an 80mm refractor which I put an iPad with the Color Softbox app running a plain white screen, over the end, not quite touching. I use Nebulosity 3 to process the images - first subtracting a bias master (made from 209 frames) from all flats and then average combining them all to create the master flat. It seems to work very efficiently... I am using a DSLR (not jealous of your lovely Atik at all...), so I guess slightly different acquisition techniques involved.

When I finally upgrade to a CCD, (I have an Atik 460EX with filters & wheel in my FLO basket, just itching to press the buy button!), I will be getting in touch for tutorials on how to actually use it!!!

Cheers.

[Martin-Devon]

It's a decent image Chris, and you've pushed the processing as hard as you probably can. The very bright centre could be due to a little too heavy on the Curves, see if backing off lets any more of the subtler details come through. Gradient Exterminator is a useful plug-in to have for Photoshop, it works well I find on greyscale images but with some colour palettes it can wash the tones out a bit - there's a low setting though which is gentle and a good all rounder. The data, framing and detail are excellent though for your image - well done!

Martin