M33 - Les Suburbs

[RobertM]

M33 - 12 x 5 mins with the Sky 90@f/4.5 with the SXV-H9 and Baader Neodymium filter, bias subtracted.  Needed something whilst waiting for the primary target to clear the trees.



Need more luminance to get rid of the noise so it's a bit too over processed for my liking.

[Daniel]

That's lovely man, are you going to do colour, would love to see the blues and reds come out in this one, you've managed to smooth the outer limbs nicely, are you using noise ninja by any chance?

[RobertM]

Thanks Daniel.  Three things that help are dithered subs, bias subtraction and just a smidgen of NN.  Bias subtraction and dithering being the main noise reducing factors, NN for the extreme low signal areas (I prefer not to use synthetic NR).  I don't know whether I'll get around to colour, there are so many interesting nebulae this time of year plus it's a pain as the astronomik colour aren't exactly parfocal at f/4.5.

[Rocket Pooch]

Good one Robert, what brightness scaling did you use for the image?

[RobertM]

Minimum pixel value was approx 12500, the core was approx 38000 and DDP parameters 12200/16000 in MaximDL - is that what you meant ?

[Rocket Pooch]

yes, do you use Photoshop and fits liberator?

[RobertM]

Yes I do use PS/FL, it was linear scaling and I selected the full range.

[Fay]

That is a really good one Robert. How does dithering work?

[MarkS]

Dithering achieves very few results.  It's nearly as bad as procrastination.

Mark

[RobertM]

And this is no time for procrastination !!!

Fay,  Dithering is a way of reducing noise from the CCD camera by slightly offsetting the image by a few pixels each sub.  This relies on the fact that some pixels generate more noise than others so by dithering we achieve something akin to binning to lower noise.

You can find an explaination here http://www.hiddenloft.com/notes/dithering.htm and also in MaximDL help.

Hope that helps.

[Carole]

Just got the joke

Re: M33 - Les Suburbs

Trying to make the suburbs sound as posh as Les Granges,,,very funny Robert. 

Also a lovely image.

Carole

[RobertM]

Was going to put 'Orpington Rive Gauche' but it didn't sound quite right somehow ...

[JohnP]

Robert - that is very good from Les Suburbs..... Like you say stars look a little saturated but more subs & less aggressive processing will sort that...well done - John

[RobertM]

Thanks John.  This was really just an opportunistic target so if I did it again I'd do some more research and probably at least double the exposure lengths and pick a better night.  The normal addage goes here - 'more subs' = 'less processing' but it's no substitute for dark skies.  Background sky levels were about 12-13000 ADU so you can imagine the signal that was lost to noise - compare that with the Iris I posted which was 37-38000 ADU (full moon) and the next (not published yet) which is Ha and only 2400 ADU.  It's doesn't take long to realise why narrowband imaging is taking off big time !

[Fay]

Robert, it is good to see such good images coming from our local environment. There is hope for us all yet.