first light on Omega Cen - help on filters?

[alocky (Andrew lockwood)]

Last night I stuck my new QSI683wsg8 on my 10" starfinder, with the Rowe coma corrector and a DMK41 guiding off the o.a.g.
I was just getting everything to focus and have a play.
So, polar alignment with a compass, no collimation, and focusing by hand, as I haven't got a robofocus adapter for this scope yet.
I took 5x2 minute subs through each of the LRGB filters, and combined the lot in pixinsight with a bit of stretching.
Question: I see red halos around some of the stars. Are these the dreaded astronomik filter halos, or is it more likely to be me over-processing excessively short sub frames?
Higher res at:
http://www.astrobin.com/37459/
Thanks for looking.
cheers,
Andrew.

[Astroman (Andrew Wall)]

No idea about the Filters, but the image is very good, thanks for showing us.

[Larryp (Laurie)]

Great image, Andrew! Resolved right to the core

[peter_4059 (Peter)]

Doesn't look like filter halo images I've seen - I thought that was an issue with the NB filters in any case. What does the stacked red filter image look like?

http://www.astronomik.com/en/news/as...r_halo_problem

[batema (Mark)]

I also love this image and have no idea about the red stars however i wonder if the colour of those stars should be more bluish in colour so i would also tend to check my blue data as well.

[alocky (Andrew lockwood)]

Originally Posted by peter_4059

Doesn't look like filter halo images I've seen - I thought that was an issue with the NB filters in any case. What does the stacked red filter image look like?

http://www.astronomik.com/en/news/as...r_halo_problem

Thanks Peter - no sign of the halos in the individual channel stacks, even when I stretch them. There wasn't a great deal of signal so I suspect I needed longer subs.

Originally Posted by Larryp

Great image, Andrew! Resolved right to the core

Thanks Larry - I think this might turn out to be a good pairing of sensor and scope.

Originally Posted by Astroman

No idea about the Filters, but the image is very good, thanks for showing us.

Thanks!

Originally Posted by batema

I also love this image and have no idea about the red stars however i wonder if the colour of those stars should be more bluish in colour so i would also tend to check my blue data as well.

Thanks - I was pleasantly surprised since it was only a couple of hours fiddling with the thing to see if it worked at all.
cheers,
Andrew.

[alocky (Andrew lockwood)]

And switching the chrominance noise reduction off during the LRGB combine step seems to have done the trick. Lots of little blue stragglers in there now.
Now I need to muck around and get some flats, biases, etc. What fun.
Thanks again all,
Andrew.

[batema (Mark)]

Good that you have it sorted. maybe tone down the red channel a little to see if stars colours will come out more. well done.
Mark

[strongmanmike (Michael)]

It looks like the red stars were larger than the G & B ones? You can get a similar but more pronounced effect when trying to combine the tiny stars a Ha filter provides..? Did you refocus for each filter?

Mike

[alocky (Andrew lockwood)]

Originally Posted by strongmanmike

It looks like the red stars were larger than the G & B ones? You can get a similar but more pronounced effect when trying to combine the tiny stars a Ha filter provides..? Did you refocus for each filter?

Mike

Thanks for the suggestion mike - these astronomiks are supposed to be parfocal but it's worth checking.

[gregbradley]

Parfocal is really marketing BS. To be parfocal filters have to be virtually the same thickness. In reality there can be subtle differences in thickness.

Mind you my latest Astrodons are fairly parfocal but others I have had were not but often very close.

Who knows, maybe the seeing was worse or some wind came up when you did your red subs or the scope was lower in the sky where stars will get fatter anyway no matter which filter is being used.

One solution is to do some deconvolution on the red master to get the same FWHM size on the stars before colour combine to match them and prevent this.

Greg.

[alocky (Andrew lockwood)]

Thanks for your suggestion Greg - the PSF tool in pixinsight is reporting FWHM values of 3.5 to 3.7 pixels for all three colour integrations on the same star, and with a bit more careful combination and calibration techniques, there are no longer any halos in the image. I'm actually well chuffed for such a short exposure as a first light test for now.
The other mystery is the absence of any yellow stars. I used to see this with the CLS CCD filter on my DSLR, and it just occurred to me that low pressure sodium is yellow, so I think I'll be leaving this filter off the front of the coma corrector in future!
Latest image...
http://www.astrobin.com/37459/C/
Cheers,
Andrew.

Originally Posted by gregbradley

Parfocal is really marketing BS. To be parfocal filters have to be virtually the same thickness. In reality there can be subtle differences in thickness.

Mind you my latest Astrodons are fairly parfocal but others I have had were not but often very close.

Who knows, maybe the seeing was worse or some wind came up when you did your red subs or the scope was lower in the sky where stars will get fatter anyway no matter which filter is being used.

One solution is to do some deconvolution on the red master to get the same FWHM size on the stars before colour combine to match them and prevent this.

Greg.

[gregbradley]

That's great Andrew. I found the aligning plugin for CCDstack was the end for these little registration errors some programs can have. Its very accurate and worth the $99.

Greg.

[Ross G]

Very nice photo Andrew.

Sharp and detailed.

Ross.