47 Tuc (another try)

[traveller]

Managed to get a few more shots of 47 Tuc last night between the clouds.
15 x 50 sec at 1600 and 13 x 90 sec at 800. Equal darks.
DSS and photoshop (levels, curves and gradient)
I am reasonably happy with the result, but comments welcome.
Muchos gracias
Bo

[jenchris]

This appears to be taken with the ed 80?
I'm surprised that the colour is a bit drained and red tinted with so much info that you obviously acquired with so much exposure.

I would try stacking again using different parameters.
There should be much better colour in there.
Sorry I dont have any suggestions as to values to use

[Rex]

Hi Bo, that's a huge improvement on the last try so your heading in the right direction. In fact with an adjustment to the colour balance I think it will be a cracker.

I hope you don't mind but I had a very quick play. All I have done here is adjusted the colour balance of all three layers, shadows, midtones, and highlights to remove the red and increase the yellow. I then did a slight histogram stretch to bring it out a little further. Hope that helps, keep them coming as I can see a huge improvement in your images, your doing great.

[traveller]

Thanks Jennifer, I am following this tutorial here http://www.stevebb.com/deep_sky_stacker.html The only difference is I selected Sigma-Kappa clipping for the light and dark frames instead of Average. I will have another go at it using Average and see if it will make any difference.
Also, when I save the stacked TIFF file as a 32 Bit Rational file, and converting it to a 16 bit TIFF file in PS, the entire photo was way overexposed and the core was totally blown out. But when I saved the file as a 16 bit TIFF (which is where this photo was made), all the details were preserved. Can anyone explain to me why this is the case? :shrug::question::help:



Thanks Rex, I am still learning the finer details of processing as you can see. I appreciate your help, so please keep suggesting on how I can imprve them. A larger file of the same file is here http://www.astrobin.com/120690/
I will have another go at processing and see if I can remove some of the red and increase the yellow. :thumbsup::thanx:
Bo

[raymo]

Good try Bo. Your stars are elongated, so the tracking seems to be a little
off. Also, the stars look bloated, was the focus spot on? You need some shorter subs to avoid burning out the core of 47. As a digital newbie I
wouldn't dream of giving advice on digital matters, but these are not
digital matters.
raymo

[cometcatcher]

Generally speaking those stacking parameters only make a difference as to what they reject. Median etc will reject more space junk - satellites, meteors, asteroids than an average stack will, otherwise the main object remains the same. Don't use maximum unless you are hunting asteroid trails.

[traveller]

Thanks Raymo,
Yes, there was a very slight drift in the mount in the Dec axis, but I didn't bother redoing it as I can see the clouds literally drifting in.
The focus is a bit soft, I manged to get FWHM at 3.8 in Backyard EOS (but it was imaging around 4-4.5), the seeing wasn't great as there was lots of moisture in the air.
Bo

[traveller]

Thanks Kevin,
What about the advanced stacking parameter and compute the number of detected stars to around 50, what is the logic/reason behind that?
Bo

[cometcatcher]

Processing time, that's all. More stars take longer to compute and more than 50 are not needed.

Regarding the colour cast, this is from the modified camera? You may need some form of filtering to get a nicely balanced starfield. Modified cameras are great for Ha nebula but can be a bit red shifted for other objects. Make sure you are at least using an IR/UV cut filter. Maybe try a 2" green or blue filter for starfields. I've found the Baader Semi-Apo filter has a nice balance for nebula and stars and also cuts UV/IR. It's a bit expensive but the Skywatcher clone is cheaper and does the same thing.

[LightningNZ]

Kappa-sigma averaging is the best way to go, but you really want to have at least 30 frames (of all types) to get a good sampling. Median stacking is effective at rejecting nasty blips (meteors or planes or whatever) but it's not a good predictor of the true mean. Checking out Shiraz's posts in the astrophotography chat forum for more info.