M101 osc success?

[Adreneline]

I've been trying to get a half-decent result of M101 for what seems like ages; I am hoping this maybe getting somewhere close. It comprises 10 x 600s subs from an Atik 414ex osc along with 50 off bias, flat and dark frames, all processed in PixInsight. I'm still not convinced I've got the focus sorted but hopefully I'm getting close. Any comments or advice would be welcomed. Thank you.

Adrian

Skywatcher ED80DS PS + NEQ6 Pro + Atik 414ex osc

Finder/Guidescope + Altair GPCAM IMX224 + PHD2 

Sequence Generator Pro + PixInsight

[JohnSadlerAstro]

Hi,

Really nice image, this is my next target so its nice to see what I can expect. I would say that the focus is a tiny bit soft, not much though--I am used to a Newt which makes focus much easier to examine . Otherwise, though, you have an enormous amount of detail already! Perfect focus and that will be amazing, full stop!  

John

[tomato]

Nice shot Adrian, I like your clean, even background sky, no doubt achieved by use of your calibration frames. Contrast this with my lazy  effort using an Atik 314 OSC, with no such calibration, and hence hot pixels, processing artefacts and dust bunnies galore.

[Adreneline]

Thank you for the positive feedback. Focus seems to be a real issue for me; no matter what I do I still get what I feel are oversized stars! Have to say I quite like the 'psychedelic coloured stars' effect - just imagine if it really was that colourful!

[wimvb]

Good result.

The galaxy has a colour cast that is easy to remove. In PixInsight create a preview that contains the galaxy, and one that contains only background. Use the background preview as a reference in background neutralization, and both previews as reference in color calibration (uncheck the structure checkbox, galaxy preview is white reference).

But you may already know this. In that case, ignore everything but the first sentence in my reply.

[ollypenrice]

I do think focus is suspect. This should not be difficult to fix. You could use a Bahtinov mask and/or a measurement in full width half max. If using FWHM make your sub exposures are 3 seconds or so to even out the seeing.

I'd also look at the colour balance. The image has a bias towards red from the faint background sky, through tha galaxy, to the stars themselves.

Let's be clear, you have a detailed image of a very faint galaxy, but I'm concentrating on what I think could make it even better. It is pretty good for 10x10 minutes. People routinely spond 20 hours on this one.

Olly

[Adreneline]

Thanks for the helpful feedback Wim and Olly. I did carry out a background neutralization and colour calibration using Preview panes but maybe I am not fully understanding what is going on there - I need to take another look and have a good read at the Keller book again. Colour is a tricky area for me - I spend a lot of time looking at images of galaxies on the web - there as as many different colour renditions as there are images! I sometimes think gray scale would be easier  I am probably guilty of oversoing the Colour Saturation process.

Regarding focus I use the focus routine built into SGP with a Skywatcher focus unit and HitecAstro remote focus control. I get a nice 'V' shaped curve and it appears to focus but then when I process the images the results are not as clean as would like. I have checked in the past with a Bahtinov mask and it appears to agree the image is focussed. Should I be considering using a UV/IR cut filter in the optics chain? Would that help with focus and definition/contrast?

Once again many thanks for the helpful comments and suggestions - they are very much appreciated. I am intent on extracting every last bit and photon from my osc.

Adrian

[ollypenrice]

16 minutes ago, Adreneline said:

Thanks for the helpful feedback Wim and Olly. I did carry out a background neutralization and colour calibration using Preview panes but maybe I am not fully understanding what is going on there - I need to take another look and have a good read at the Keller book again. Colour is a tricky area for me - I spend a lot of time looking at images of galaxies on the web - there as as many different colour renditions as there are images! I sometimes think gray scale would be easier  I am probably guilty of oversoing the Colour Saturation process.

Regarding focus I use the focus routine built into SGP with a Skywatcher focus unit and HitecAstro remote focus control. I get a nice 'V' shaped curve and it appears to focus but then when I process the images the results are not as clean as would like. I have checked in the past with a Bahtinov mask and it appears to agree the image is focussed. Should I be considering using a UV/IR cut filter in the optics chain? Would that help with focus and definition/contrast?

Once again many thanks for the helpful comments and suggestions - they are very much appreciated. I am intent on extracting every last bit and photon from my osc.

Adrian

I'm notoriously stone age but I've seen enough Hitecastro boxes and auto focus routines acting the goat here to last me a lifetime! Why not run your robotic focus routine and then test it using either a B mask or an FWHM measurement or both? 

Olly

[Adreneline]

Hi Olly. I can do that  I'll give the B mask another go and see if that improves the end result. I did wonder if the draw tube was very slowly slipping. At the end of the M101 session it moved as I disconnected the cables and I subsequently discovered the friction device was not accurately aligned with the focus unit drive shaft and it required very little effort to move the draw tube unit. I was wondering whether it may have slightly worked its way out as the scope moved to a more vertical position. Maybe I should be focussing throughout the session - between subs - rather than just at the start of the session.

Thank you again for the advice.

[wimvb]

Downloaded your image, and did the unforgivable: colour calibration on a stretched jpeg image, as per my earlier description. Followed by the very forgivable: star reduction with morphology transform.

Doing colour calibration on a stretched jpeg can never completely clean an image, and here the colour was pushed over to the other side. But it does show the potential.

Ideally, you apply background neutralization and color calibration directly after getting rid of gradients (dbe), before any other processing.

Hope you don't mind.

[Adreneline]

Hi Wim. I don't mind at all - I am grateful for the time you have taken to give me an idea of what I should be aiming for. I'll give it a go. Thanks again

Adrian

[alacant]

Hi. Nice shot. Yeah, this one is really dim. Either you have fwoabw 'refractor' stars, or you missed focus a touch. I don't think there's anything bright enough to focus upon  in the field or anywhere close so it maybe best to swing over to one of the plough stars, focus there and then recompose on the galaxy. HTH.

[Adreneline]

OK - re-background-neutralized, re-colour-calibrated and re-colour-saturated - hopefully it's heading in the right direction.

Thank you again Wim