NGC 55 (Will the real Sculptor galaxy please stand up!?)
My Synscan handset lists "Sculptor galaxy" and NGC 253 as 2 objects. After digging about I gather NGC 55 is being called the "Sculptor galaxy". I guess they're both in Sculptor......
Anyway, as a first semi-serious DSO stacking effort thought I'd pick a bright galaxy, however I gather NGC 55 is a bit tricky from reading around tonight? Forgive my dodgey processing - trainer wheels on. Original stacked image from DSS and my attempt at processing attached.
Took about 90 x 30sec, mainly ISO 1600, some 800 with about 8 x 1min thrown in. MPCC and IDAS in use, no guiding, and oops - no viewfinder cover on....
I've fiddled quite a bit and can't get rid of that noise/sky background surrounding the galaxy without losing a lot of galaxy detail. Any pointers guys?
All done with in-camera noise compensation turned on and no darks/flats, so I guess that's one big reason.
The glow around NGC253 is always tricky to remve i think.
Theo is right, the flats will help with vignetting.
technically to remove the left over glow without affecting the galaxie too much, there are a couple of ways of doing it.
The one i tend to use is :
copy the image twice.
blur copy 1 in gaussian blur maximally
blur copy 2 just a bit and invert (black becomes white
copy and paste copy1 onto original (you would of course want to have tucked away a copy of the original so it is saved safely without alterations)
in layers select the mask icon, Alt click on it copy and paste into that window the copy 2
you're now pasting a blur onto the original with a mask of everything but the galaxy
select the type of blending works best and that should help
you'll need to experiment with size/intensity of mask, blending mode, blending transparency etc
but that should help remove some of the glow around the galaxy without touching the galaxy itself.
[quote=RobF;373632]My Synscan handset lists "Sculptor galaxy" and NGC 253 as 2 objects. After digging about I gather NGC 55 is being called the "Sculptor galaxy". I guess they're both in Sculptor......
quote]
NGC 253 is also known as the " Silver Dollar " galaxy by our North American friends.
Oh, i think the fact you have no darks/flats IS "A BIG REASON"!.
Not only you got some heavy vigneting, but as you said a little noisy too.
You need to do these two tasks when using a DSLR.
Theo.
Thanks Theo and Frank. It probably sounds like heroic ignorance, but until I fully understood flats and darks I wasn't planning to use them. I could get my head around using darks to clean up sensor noise, but didn't appreciate what a difference flats could make.
I always thought vignetting was something that happened at the edges of a photo as optics or focuser aperture impinged on getting a full image. I think I understand a bit better now why both are required - have just been reading up on flats at:
I must find and devour a good astrophotography text.
Quote:
Originally Posted by spearo
Rob,
good on you for delving into DSOs.
The glow around NGC253 is always tricky to remve i think.
Theo is right, the flats will help with vignetting.
technically to remove the left over glow without affecting the galaxie too much, there are a couple of ways of doing it.
The one i tend to use is :
copy the image twice.
blur copy 1 in gaussian blur maximally
blur copy 2 just a bit and invert (black becomes white
copy and paste copy1 onto original (you would of course want to have tucked away a copy of the original so it is saved safely without alterations)
in layers select the mask icon, Alt click on it copy and paste into that window the copy 2
you're now pasting a blur onto the original with a mask of everything but the galaxy
select the type of blending works best and that should help
you'll need to experiment with size/intensity of mask, blending mode, blending transparency etc
but that should help remove some of the glow around the galaxy without touching the galaxy itself.
hope this helps
frank
Frank - many many thanks for your Photoshop advice. I surmised it would be possible to do some sort of masked cleanup, but had no idea where to start. I'll try as you suggest, but must admit I struggle to keep up with much of what you've described - that means I'll learn more though!
And in the future will try to avoid collecting noisey data that needs excessive post-treatment ideally.
Quote:
Originally Posted by Bassnut
As Theo says, use flats/darks, and 5 min subs.
Fred - I know it probably sounds primitive, but this was done without any guiding, so I thought I better limit the length of my subs. Even with guiding I understood sky glow/pollution to become more problematic with increasing exposure time. Must confess still try to come to grips with difference between say 5 x 1min subs and 1 x 5 min sub. Again - I guess I've got plenty of learning fun left ahead of me in the future.....
Thanks Dave. I'm a bit miffed I spent that much time imaging the fainter Sculptor galaxy when I really meant to go after the brighter NGC 253. We had that problem at your place recently when I couldn't figure out why my quick fuzzy Sculptor shots were a bit different to yours (and then realised the scopes were pointing in slightly different directions! )
You'd think I'd have learned which was which that night.
Anyway, had fun. Was thinking this might be a good exercise to prepare for an attempt at M31 at Ron's if everything comes together.
I have said this on some other posts, but just use a white shopping bag that you get from Safeway etc.
The white semi pearl sheen plastic bag does a great job when you place it in front of your scope and point it to a brightish object.
I just point it to the wall with a low power light shining on the wall.
Its cheap, and it works.
But if you like to build, then make one.
I always like to start with a low tech solution - at least until the quality of my skills starts to reach that of my equipment!!!
Quote:
Originally Posted by Gama
I have said this on some other posts, but just use a white shopping bag that you get from Safeway etc.
The white semi pearl sheen plastic bag does a great job when you place it in front of your scope and point it to a brightish object.
I just point it to the wall with a low power light shining on the wall.
Its cheap, and it works.
But if you like to build, then make one.
NGC 55 (Will the real Sculptor galaxy please stand up!?)
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