jase
03-10-2007, 12:51 PM
$ Here's a coin $...
Hi All,
Well it’s been a while between new posts in the DS forum. OS work commitments and other tasks have consumed much of my time so haven’t been as active in the imaging scene as I’d like. Still keeping tabs on the imaging work submitted by others which acts as a catalyst for getting out there and collecting photons.
Anyway, without further ado, I’m pleased to present NGC 253 (http://www.cosmicphotos.com/gallery/image.php?fld_image_id=115&fld_album_id=12), dubbed “The Silver Coin Galaxy”.
The barred spiral galaxy NGC 253 is the brightest member of the Sculptor group of galaxies. The group is estimated as being nearest to the Local Group of galaxies which includes our Milky Way galaxy. NGC 253 is one of the dustiest galaxies known. Dark dust patches conceal much of its spiral structure, also masking the HII regions. The galaxy appears elongated as we see it from an edge-on perspective. In spite of the dust, two spiral arms are subtly visible towards the edge of the galaxy with numerous bluish clusters of young stars. NGC 253 is approximately 10 million light-years distant.
About the image;
This is an LRGB composite consisting of 5.5 hours of data (L:120min; R:70min;G:70min;B:70min) taken over a few nights to beat the rising moon light contaminating the chrominance data (RGB). This isn’t much data to work with for such a slow telescope (F/9) and a dim target such as NGC 253. I wrestled for hours chasing colours. I haven’t got a good handle on the Astrodon filters and the colour balance characteristics they produce. Even after manual normalisation of the individual RGB channels using pixel math, I still couldn’t get the right balance with a 1:1:1 ratio (as per filter specs.) so opted for a more suitable balance. Kept a natural feel. The exact problem occurred with the Helix nebula image. The RGB data used 10min subs binned 2x2 to give a good S/N ratio. The RGB data is actually quite good, but on reflection, I should have also taken some shorter 5min subs to bring the star colours back. 10min subs was ideal for the galaxy chrominance, but pushed the stars too far (thus lost their colour information). Overall, I feel I’ve captured the “essence” of the galaxy reasonably well with handful of background galaxies dotting the scene. NGC 253 is quite high late in the evening this time of the season so lends itself well to getting good resolution as it crosses the meridian – darn those GEM flips!
Image processing;
All subs calibrated/reduced (dark, bias, flat), registered and Sigma-Reject combined in MaximDL. Luminance deconvolution performed in CCDSharp – two iterations. Colour combined chrominance (RGB) in MaximDL to achieve corrective colour balance ratios. Luminance initially stretched in MaximDL using DDP – no sharpening filters applied. Both images loaded into PS for further processing. Chrominance image stretched using shadow/highlights tool. Both images (luminance and chrominance) had gradients, but nothing considerably hard to deal with - created basic subtraction masks to remove these. Then moved on to cleaning both luminance and chrominance layers with the self-healing brush – removed colour inconsistencies and minor dead pixels that were not clean up in the combine function. Applied two selective layer masks, one to reduce noise in the dim areas and the other to highlight features of interest. Actually, I was rather slack with the noise reduction. Could have been a pushed the settings hard to better correct some colour noise.
I will try to make sure there is not such a long delay between posts. Though, I’m happy to produce a few quality images a year, than pump out a crap one every fortnight!
I hear the FSQ calling - back to wide fields is in order.
Well, that’s my couple of cents worth <pun intended>;), thanks for looking and hope you enjoy it.
Cheers
Hi All,
Well it’s been a while between new posts in the DS forum. OS work commitments and other tasks have consumed much of my time so haven’t been as active in the imaging scene as I’d like. Still keeping tabs on the imaging work submitted by others which acts as a catalyst for getting out there and collecting photons.
Anyway, without further ado, I’m pleased to present NGC 253 (http://www.cosmicphotos.com/gallery/image.php?fld_image_id=115&fld_album_id=12), dubbed “The Silver Coin Galaxy”.
The barred spiral galaxy NGC 253 is the brightest member of the Sculptor group of galaxies. The group is estimated as being nearest to the Local Group of galaxies which includes our Milky Way galaxy. NGC 253 is one of the dustiest galaxies known. Dark dust patches conceal much of its spiral structure, also masking the HII regions. The galaxy appears elongated as we see it from an edge-on perspective. In spite of the dust, two spiral arms are subtly visible towards the edge of the galaxy with numerous bluish clusters of young stars. NGC 253 is approximately 10 million light-years distant.
About the image;
This is an LRGB composite consisting of 5.5 hours of data (L:120min; R:70min;G:70min;B:70min) taken over a few nights to beat the rising moon light contaminating the chrominance data (RGB). This isn’t much data to work with for such a slow telescope (F/9) and a dim target such as NGC 253. I wrestled for hours chasing colours. I haven’t got a good handle on the Astrodon filters and the colour balance characteristics they produce. Even after manual normalisation of the individual RGB channels using pixel math, I still couldn’t get the right balance with a 1:1:1 ratio (as per filter specs.) so opted for a more suitable balance. Kept a natural feel. The exact problem occurred with the Helix nebula image. The RGB data used 10min subs binned 2x2 to give a good S/N ratio. The RGB data is actually quite good, but on reflection, I should have also taken some shorter 5min subs to bring the star colours back. 10min subs was ideal for the galaxy chrominance, but pushed the stars too far (thus lost their colour information). Overall, I feel I’ve captured the “essence” of the galaxy reasonably well with handful of background galaxies dotting the scene. NGC 253 is quite high late in the evening this time of the season so lends itself well to getting good resolution as it crosses the meridian – darn those GEM flips!
Image processing;
All subs calibrated/reduced (dark, bias, flat), registered and Sigma-Reject combined in MaximDL. Luminance deconvolution performed in CCDSharp – two iterations. Colour combined chrominance (RGB) in MaximDL to achieve corrective colour balance ratios. Luminance initially stretched in MaximDL using DDP – no sharpening filters applied. Both images loaded into PS for further processing. Chrominance image stretched using shadow/highlights tool. Both images (luminance and chrominance) had gradients, but nothing considerably hard to deal with - created basic subtraction masks to remove these. Then moved on to cleaning both luminance and chrominance layers with the self-healing brush – removed colour inconsistencies and minor dead pixels that were not clean up in the combine function. Applied two selective layer masks, one to reduce noise in the dim areas and the other to highlight features of interest. Actually, I was rather slack with the noise reduction. Could have been a pushed the settings hard to better correct some colour noise.
I will try to make sure there is not such a long delay between posts. Though, I’m happy to produce a few quality images a year, than pump out a crap one every fortnight!
I hear the FSQ calling - back to wide fields is in order.
Well, that’s my couple of cents worth <pun intended>;), thanks for looking and hope you enjoy it.
Cheers