Ngc5139

[DavidTrap (David)]

My first offering in some time.

Takahashi FS-102
QSI583
30 second Luminance (Bin1) and RGB (Bin2)
I've been looking back at other examples of this object and realise I might need to do some longer subs - mine might be stretched a bit too much, but some shorter ones will be necessary to maintain the detail in the core.

Rick has suggested the blue channel looks a bit odd, especially around the core - might be due to a weird colour balance - trying to find my feet in PI after a long hiatus.

Comments welcome.

DT

Link to image (1.5Mb)

[jase (Jason)]

David, I can't see anything wrong with the blue channel, at least at a histogram level. Cluster resolves well. Only concern would be the blue/green fringing on some of the stars. This could be a registration error though I suspect you have probably got a few subs with a higher FWHM value that is influencing the blue/green masters. Try removing the culprit poor subs to get matching or as close to FWHM values across the RGB masters. Sometimes less subs of a good quality is more than many subs of mediocre quality.

[DavidTrap (David)]

Thanks Jase,

I'll run them through CCD Inspector and see if there are any outliers.

It's also taken with a Fluorite Doublet, so there will be some chromatic aberration. I can't recall if I was doing my usual focusmax run between filters - was having a few equipment issues that evening...

DT

[RickS (Rick)]

Hi David,

One thing I just noticed is that the image has an ICC Profile of "Display". You probably want to modify your PI colour management setup (under the Edit menu) and set your default RGB profile to one of the device independent colour spaces. I use ProPhotoRGB but AdobeRGB would be a good choice too. The second thing to do is to convert final content for the web to sRGB so it will display at least halfway OK on non colour managed browsers and crappy screens. You can use ICCProfileTransformation in PI or Edit>Convert to Profile in PS.

Pixel peeping at the full res image the thing I noticed in the blue is from halos around some of the blue straggler stars. A couple have purple halos too. At lower res it looked a bit like a blue cast around the outer concentration of the glob.

Cheers,
Rick.

[DavidTrap (David)]

Thanks Rick,

Will give that a try later today.

DT

[DavidTrap (David)]

Ok,

Colour profiles are changed.

I ran the individual subs through CCD inspector. FWHM values for Luminance and Green are in the 3-4" range. Red and Blue are in the 4-5" range. I think I was having some issues with the focuser that night, so may not have done my usual routine. Will try to collect some data for comparison with more strict adherence to my usual processes.

DT