Galaxy NGC 4945

[rogerg]

Hi all,

Being confined to home due to my ankle problems I've had to give up on the nightscape/wide field astrophotography for now and go back to the observatory.

Here's a 15x10min exposure of NGC 4945 from last night. I captured colour data (a little dodgy but it's ok) but am useless at getting colour frames in to make an LRGB :shrug:

Regards,
Roger.

[Larryp]

Nice image, Roger. Hope your ankle is better soon

[Bart]

Looks reasonable, for sure.

Why not put up your calibrated and stacked raw frames in fits format somewhere so others can download it and work with it and then post back into your thread their results.

Would be fun and a great way to see the different methods and software that people use.

[rogerg]

Thanks :)



I wouldn't mind doing that, must work it out. Maybe I can put it in a public dropbox or such. Will see if I can when I'm next home. :thumbsup:

[multiweb]

Details in the dust lanes look really good. Nice one. :thumbsup:

[rogerg]

Thanks Marc :)

I was impressed at the dusty lanes showing considering it was taken near full moon :)

[astronobob]

Thats a Fine looking Galaxy Roger, The 'L' channel shows the emmiting light graciously from within this target, Good stuff :thumbsup:
And all the best with colour and Ankle .

[blink138]

i like it a lot roger!
it says that you are 51km from me roger but i dont know how you can get a 10 min exposure..... mine is saturated after 4 tops!
does 50ks make that much difference?
pat

[rogerg]

Thanks :thumbsup: Ankle is improving but probably surgery yet to come :)



Pat it does make quite a difference I think. From up here I can see the milky way and magellanic clouds naked eye quite easily (especially the LMC and milky way). That would say something about the general background brightness. Having said that, I have a friend in the heart of the suburbs who does very good imaging (with a pretty good setup!) and long exposures. Using Apogee CCD. I'm not sure what is max exposure time is though.

I've done 40 minute integrations up here in the past with my ST7 (high QE), when I was doing my HDF-S attempt: http://rogergroom.com/projects/hubble-deep-field-south/
These days I'd stick to 20mins just because of "return on investment" for the time, but I needed to try 40mins. :)

[rogerg]

A suggested, I have made public the stacked LRGB frames in case anyone is happy to have a go at colour combining them. I have tried briefly and get no significant colour variation, just a muted gray/blue or such.

Below is a link to a zip file containing the four .FIT files in my public dropbox folder:

https://dl.dropboxusercontent.com/u/54948522/NGC%204945%20stacked.zip

[rogerg]

Here's my LRGB version, obviously lacking some colour balance and variation in colour ... but just can't seem to get it better ...

Resized down and compressed to fit under 200kb.

[blink138]

geez roger i think the little colour you have done has given it more depth and it does seem sharper for some reason
pat

[rogerg]

There is a lot more data in it, both RGB and several more L frames, so that will be where the sharpness is coming from :thumbsup:

[jase]

Great result Roger! You've got solid luminance data to work with. All the details are there, thats for sure. I'm not sure what has happened to the RGB data, it doesn't look balanced as you suggest. I had a quick look at your raw red, green and blue FITS. The signal does not get much higher than your background ADU which I was initially very surprised to see given the 2x2 binning. You can however drop the background substantially and begin to see the colour balance needs to adjustment - needs greater blue and a small amount of green to counteract the magenta shift. Overall with some further repros, I think you could get a little more from the data if you're inclined. Thanks for sharing, and well done.

[Ross G]

Great looking galaxy photo Roger.

Ross.

[rogerg]

Thanks for your vote of confidence Jase!

Yes, the raw frames needed much stretching, dropping the background etc. I went about doing that in Photoshop when I layered them :shrug:

Perhaps I should be doing longer exposures in blue? I have been working on the theory that it's best to have all RGB exposures the same and balance them in software afterwards.


Thanks Ross :)

[naskies]

Nice work, Roger - I'm very jealous of your new "remote" set up :) I'm a big fan of this galaxy too.

What altitude were your blue exposures shot at? I know that some people shoot correspondingly longer B exposures to account for attenuation, while others will wait for the object to rise to a higher altitude (i.e. shoot a sequence such as R R G G B B B B G G R R during the night to maximise the altitude of B subs, if that makes sense).

[rogerg]

:) Thanks Dave. That's an interesting idea shooting at different altitudes! These were all taken at about the same altitude as it happens. I typically started an hour or two before it crossed the meridian and finished an hour or two after it crossed the meridian.

PS. The challenge with such a setup is using it to it's full potential and not feeling like the wonderful resource is being wasted.