Ngc 104

[Atmos]

I’m still trying to figure out the best way of getting good colour from drizzling and deconvolving OSC data. Might have to try not stretching the colour data a lot before combining it with the luminance.

At any rate, this is 24x300s with the D810. Centred on 47 Tuc but it also has a few background galaxies and numerous extragalactic star clusters :)
Yes, the core is definitely burnt out. I’ll need some 60s exposures at some point in the future to fix that.

High Res Version (https://www.astrobin.com/full/370106/0/)

[Lee]

That's a great result - pinpoint stars.... what scope did you use?

[Atmos]

Apart from the burnt out core I’m pretty happy with it.
It was taken with a Sky Rover 130mm Sextuplet.

[glend]

Colin, nice image. If you reduce the opacity of the luminance layer the colours should pop better. That works for me (well in Photoshop), but I don't know how your processing it. I usually limit luminance opacity to 17-20% depending on the object. I have found that Ha can work well for as luminance on some objects, it tend to give you shaper stars, at least on my TS refractors. How are you shooting luminance with a OSC?
I am usually shooting mono through filters, so that also gives you the ability to boost colour saturation on the individual layers, which can also improve overall colour coming through. You should be able to play around with your OSC saturation, worth a try. Still whether 47 Tuc or Omega C, there is not a lot of native color there anyway.

[RickS]

Nice detail, Colin. How did you do the colour calibration?

The biggest problem I found with my D800 for astro was that the channels would saturate at different levels and attempting to push the colour caused pink stars.

Cheers,
Rick.

[Placidus]

Glen:

At face value, that would mean that you have just thrown out 80 to 83% of your luminance data. You may as well have not taken it if you are photographing LRGB.

If you are photographing RGB and producing a fake luminance layer from the colour data (with a view to reducing colour noise, which is the only conceivable reason) your maths will have negligible effect. It is easy to prove this: the values of neighbouring pixels have no effect on any given pixel.

The way to reduce colour noise without losing saturation would be to separate into L and RGB, filtering the RGB to reduce colour noise without affecting topographic data or losing saturation, and finally recombining the L with the RGB.

There are tedious methods converting RGB into HSV for example, and then topographically filtering the H without filtering the S or V, and converting back to RGB, which achieve much the same result, but if you've already separated into L and RGB, there is little point.

In summary, the way to increase the saturation is to increase the saturation, not to reduce the opacity of the luminance layer.

Mike

Postscript: I wonder if Glen is adding the luminance layer with properties set to "Normal" instead of "Luminance". That would explain the confusion.

[Atmos]

Processing was quite simple:
Drizzle Integration
Gradient removal
Photometeric Colour Calibration against G2V (normal colour calibration made 47 Tuc white)
RGBWorking Space
Luminance extraction
Deconvolution on synthetic luminance
Stretch both L & RGB
LRGB Combination
Saturation boost
Green bias removal

You are right Glen in that Ha will give sharper stars and it is an interesting thought for globular clusters, could be worth trying at some point when I’m using using my DSLR :)

Rick, with the linear data in the D810, most stars have pink cores but I haven’t found that to be an issue when stretching with the HistogramTransformation but it doesn’t work as well with MaskedStretch. I find that as the data is stretched and the PSF is drastically fattened the real star colour swamps the pink core.

I agree with you Mike and although I have heard of HSV in Photoshop I only know it as a car :lol:

[multiweb]

Nice glob. Tak sharp. :thumbsup:

[Atmos]

When I eventually get around to installing the corrector on the Mewlon 250, it will be Tak Sharp :lol:

[willik]

That is a very nice cluster of stars well taken.Quality :thumbsup:
Martin

[Placidus]

The thing we really like about this one is it looks like it looks through the eyepiece, with that super-bright moon-disc in the middle. That's hard to achieve.

[Atmos]

Thanks Martin.



Thanks Mike :thumbsup:
It is very easy to achieve though... just over exposure and saturate the core :lol:

[strongmanmike]

Yeah, this is really good Col, has a classic era Schmidt plate astrophoto look to it :thumbsup:

Mike

[PeterSEllis]

Hi Colin,
It is a nice shot. Very difficult to resolve the core on this one, 150mm Esprit can't and even the 12" can't totally resolve the core, even with a short exposure. It is nice to see the background galaxies in this shot.

Cheers
peter

[Jeff]

Nice capture Colin.

For what it's worth, I've struggled to get good color from 47 Tuc also.
Unlike with Omega Centauri.


Cheers,
Jeff

[Bart]

Great shot. Love the globs!