Southern Cross repro

[Retrograde (Pete)]

Now that my processing skill has improved marginally I thought I'd re-do a couple of old images (no chance to do any imaging lately anyway).

This is a reprocess of a 50 mm f1.7 lens image of the Southern Cross and Coal Sack. Stacked 7 x 30 second exposures at ISO 1600 using the Pentax K-5 DSLR.

The original effort had really bad CA which I've now managed to (partially) process out. The lens is one I've had since my film-camera days back in the 1980s so not sure how to go about finding a lens-correction profile for it.

Slightly higher res at http://www.astrobin.com/118148/

[raymo]

That was worth doing Pete.
raymo

[SimmoW (SIMON)]

That's a nice Sack Pete! Such a beautiful area

[cometcatcher (Kevin)]

Nice dark coal sack. Maybe a tinge green?

[Retrograde (Pete)]

Thanks Raymo, Simon and Kevin.

Originally Posted by cometcatcher

Maybe a tinge green?

Yep I think you're spot on here - thanks for pointing it out

I used a lot of noise-reduction to get rid of the purple/magenta flares around the bright stars and removing so much blue & red may have had the effect of re-enforcing the green. Most of my previous images have been a bit too purple as I usually take out too much green. I guess there's a happy medium there somewhere and I've just got to find it.

The original data isn't that great - in addition to CA, the star images off-centre are a bit funny: it was one of my first proper attempts at polar alignment after 20 years out of the hobby. My next processing challenge is learning how to fix imperfect star images.

After taking the subs I had written off the lens as unsuitable for astro work but that may have been premature - and after all who doesn't love the idea of imaging at f 1.7?

[Camelopardalis (Dunk)]

That's lovely Pete - well done

[Regulus (Trevor)]

That's a nice result Pete but I would have thought a standard 50 like this would have minimal CA so count me surprised. Still, a satisfying image.
trev

[Retrograde (Pete)]

Thanks Dunk & Trevor.

Originally Posted by Regulus

I would have thought a standard 50 like this would have minimal CA so count me surprised.

Yep me too. I might try stopping it down a little the next time I try it and see if that makes a difference.

[Rex]

Not a bad shot Pete, stars are a little bloated but detail is good and the coal sack stands out quite well. Nice job on removing the CA too.

[rjmd (RJ)]

Wow, that is really good!

[Retrograde (Pete)]

Originally Posted by Rex

Not a bad shot Pete, stars are a little bloated but detail is good and the coal sack stands out quite well. Nice job on removing the CA too.

Thanks Rex. I just had a closer look at one of the original subs and the star images away from the centre look to be affected by coma rather than field rotation.
Amongst my collection of old lenses from film days I also have a Ricoh Rikenon 50mm f1.7 so I might try that out sometime and see how it compares.

Originally Posted by rjmd

Wow, that is really good!

Thanks RJ!