Hyperstar Narrowband Bicolour: NGC6888 The Crescent Nebula

[Ikonnikov]

After a few recent clear nights I’ve finally managed to acquire some OIII to add to my previous Ha data (which I also expanded) of the Crescent Nebula NGC6888 to make my first narrowband bi-colour image.

The image is a simple Red:Ha, Green:OIII Blue:OIII mapping which seems to give ok colours for the Crescent after playing with colour weightings a bit. Upon combination I found controlling the dynamic range and colour saturation of the brighter Crescent parts and the fainter background Ha to be pretty tricky and the result is a bit of a ham-fisted compromise.

Again, I’ve found the PI deconvolution tool to be very useful in giving providing extra detail to the nebula (in addition to the usual HDR transform, LHE etc in PI) and have had my first go at star reduction in the final image (they’re quite chunky with the relatively broad filter bandwidths I need at F2.1).

Any comments/criticisms most welcome!

Final image details:

C8 Hyperstar III on HEQ5 (Pier mounted), Atik 428EX mono@-12C

Ha 32x600s (Baader 7nm)

OIII 36x600s (Astronomik 12nm)

Pre and post processing in Pixinsight

[Ikonnikov]

And here's the mono Ha image:

[Ikonnikov]

And the OIII image.

[Ikonnikov]

Full resolution uncompressed image:

http://www.astrobin.com/116115/

[wavydavy]

nice....

[nmoushon]

Did you remove the camera and change filters for each filter or did you have a filter wheel? Very nice color and star control with the hyperstar.

[x6gas]

Very nice.

The OIII looks a little bit soft to my eyes...  I guess focusing accurately at f/2ish isn't a walk in the park so could the focus be off by a touch?

[Ikonnikov]

Thanks for your comments folks.

Did you remove the camera and change filters for each filter or did you have a filter wheel? Very nice color and star control with the hyperstar.

Yes, I have to unscrew the camera to change filters (as far as I know there isn't a filter-wheel system small enough to fit on the Hyperstar adapter without causing major obstruction). However with the number of subs I was doing for each filter and with only two filters in total this wasn't particularly onerous. For LRGB I also have an OSC camera so only need to change over once to do the L (not that I've done much of this kind of imaging yet though since having both cameras).

Very nice.

The OIII looks a little bit soft to my eyes...  I guess focusing accurately at f/2ish isn't a walk in the park so could the focus be off by a touch?

Indeed, looking back at the OIII image after a bit of a break from the screen I see what you mean! I eased off a bit on the deconvolution for the OIII as SNR is relatively low, but I agree that focus is likely to be at least part of the issue too. I focus manually with the Nebulosity fine focus function although with a feathertouch microfocusser fitted it isn't as hard as it sounds. I probably don't refocus often enough to always catch temperature shifts though. There's also been intermittent thin high cloud recently which won't have helped either. I will have a closer look through my subs and play more with the deconvolution to see if I can improve what I've already got though!

[Coco]

Very nice, the OIII is terrific..

[Gina]

Very nice

[D4N]

Very nice, have you tried the filter drawers TS make? They aren't much bigger than a 2" filter so probably similar size to your camera.

Still have to manually change but at least you don't have to remove the camera and unscrew the filter. Those filter threads are a real pain.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

[Mav359]

There is a cartridge system you can buy for changing filters, it'd mean buying a different camera adaptor for the hyperstar and at least 1 filter tray but i don't think they are cheap

You can have a look at them on the starizona website.

[Mav359]

Oh by the way that TS drawer system D4N mentioned wont work (sorry), the camera adaptor (ive been told) is specific lenght for your combination of hyperstar and camera, if you add something between the camera adaptor and the camera the hyperstar system won't work nearly as well if at all. The system that starizona produce is built so it fits inside the camera adaptor so it doesn't change the light path.

[ollypenrice]

I like the nebula and the strong O111 shell. As is sometimes the case with the Hyperstar the stars are on the large side, perhaps because of the slight focus drift in O111. I might cut the black point a bit less aggressively, but this is getting picky! You have a strong image with the outer shell playing nicely.

Olly

[D4N]

Oh by the way that TS drawer system D4N mentioned wont work (sorry), the camera adaptor (ive been told) is specific lenght for your combination of hyperstar and camera, if you add something between the camera adaptor and the camera the hyperstar system won't work nearly as well if at all. The system that starizona produce is built so it fits inside the camera adaptor so it doesn't change the light path.

Ah I should have known it would be foolish to expect the solution to be either simple or cheap.

Spacing seems to be a pain for a lot of scope types, what's wrong with just making things short and supplying a bunch of spacer rings?

Sent from my iPad using Tapatalk

[Ikonnikov]

Definitely agree on the fat stars and soft focus for OIII; data for this image was acquired before I started using an aperture mask (Hyperstar @F2.66) and motorised focusing to try and address these issues (e.g. in http://stargazerslounge.com/topic/225222-testing-a-tamed-c8-hyperstar-ic1396-elephant%E2%80%99s-trunk-nebula-in-h-alpha/). They do seem to help although we're not exactly talking premium astrograph quality subs and my processing skills are pretty unrefined/generic at the moment!  Will post a couple more images with this set up shortly though.