Messier 83 (Southern Pinwheel)

[David Fitz-Henr]

Hello all,
Well it's been a long time between drinks; I can't believe that I last posted an image here back in 2014!?! In that time I have revamped my telescope tube to eliminate some flexure and to cater for the different back-focus requirements of a Paracorr (replacing the ASA Wynne corrector). This was followed by a major failure of the mirror (crack developed due to thermal stresses) which I have replaced with a Royce mirror. Then some personal issues... Anyway, I have been collecting some data over the last couple of years and have finally processed an image after coming back up to speed with Photoshop / etc.

M83 Full size version: https://pbase.com/david_fitz_henry/image/173687872

[Geoff45]

Impressive image Dave. Good detail right down to the core. Some tantalising detail in the two little galaxies at the top—most pics just show them as nondescript blurs.
Also you’ve brought out a third little galaxy. I’ve never noticed that one before
Geoff

[Dave882]

Lovely shot!! Fantastic detail and yeah those background galaxies are very cool too

[strongmanmike]

Welcome back Dave, with that new improved beast of yours, the sky is the limit....like me with a brand new and improved site, you'll have to re shoot everything now too :P :thumbsup:

Mike

[David Fitz-Henr]

Thanks guys!
Actually, I have just updated the image (realised that I had the Ha colour layer tweak turned off when I flattened the image in photoshop) - still a bit rusty I suppose. Kind of you not to notice :lol:

[marc4darkskies]

A wonderfully sharp, natural looking image! :thumbsup:

[David Fitz-Henr]

Thanks Marcus, I'm reasonably happy with it albeit a little rusty still ;)

[alpal]

Great image David,
it's really sharp - you must have had good seeing
and you've gone deep with heaps of background galaxies.


Could you please tell us more details about that replacement mirror?
What type is it - a conical? and what is the f number?
Do you have any photos of the "Bunyip 12.5" Newtonian Astrograph -
inside and out?


cheers
Allan

[David Fitz-Henr]

Thanks Allan.
It is a conical mirror that I purchased from R.F. Royce to replace the original conical mirror that developed a crack and ruined the figure. It is f/5.05 natively, but I am using a 3" Paracorr that changes it to an effective f/5.8. I have pictures of its construction here: https://pbase.com/david_fitz_henry/317_5mm_astrograph

[alpal]

Thanks David,
that's an impressive setup -
no wonder your pictures are so good.
f5.8 is giving you a nice image scale to zoom in on galaxies.
Did you measure the FWHM for the pic in this thread?


cheers
Allan

[David Fitz-Henr]

f/5.8 and a pixel size of 9microns yield a scale of 0.99 arcsecs/pixel.

I took 41 lum subs ranging from an average FWHM of 1.87-2.97 arcsecs. I then divided these into 3 groups to produce 3 luminance combines for high res / high+medium res / all subs (all done in Registar & CCDStack). In Photoshop I create masks and blend the three using the high res image for the bright regions, medium+high res for fainter regions, and all subs for the background.
I take the R/G/B subs when the seeing isn't good enough for luminance (but still not too poor ;)).

[alpal]

Thanks David,
that sounds like a very wise way to process.
Smaller pixels might have given a bit extra
and maybe 3 x drizzle on the galaxy would have given more detail too?


cheers
Allan

[David Fitz-Henr]

Sorry Allan, I "misspoke" - I meant to say "an average FWHM of 1.87-2.97 arcsecs" (not arcsecs / pixel - now corrected in my previous reply). At an image scale of 0.99 arcsecs / pixel this is fairly ideal, so nothing to be gained by drizzling.