ngc7635 The Bubble Nebula in Ha

[Dave Smith]

The week before last I intended to capture this target but it all went wrong and I couldn't find it. It wasn't helped having my finder not properly aligned.

Last Thursday night starting at around midnight (I was out during the evening) I took things carefully, using the Moon to get rough focus and to align the finder. Then a few star hops beta Cass -> M52 ->Bubble. I chose to goto M52 before the Bubble as I was sure I would be able to see that with a short exposure and was unsure how long before I would see a recognisable bubble.

It was taken with my Vixen FL102S with a W.O. type III reducer 0.8x. This is my first attempt at using a reducer with that scope and I seem to have got away with it with the small sensor of the Atik 314L+.

2h 20m of 10 minute subs together with darks, flats and bias. Calibrate and stacked in MaximDL and processed in Photoshop CS2.

Dave

[Mark72]

nice work Dave,

It's a very recognizable bubble;)

Mark

[michael.h.f.wilkinson]

Neat bubble! Very nice

[rwilkey]

Dave, that's amazing, well done!

[Dave Smith]

Many thanks Mark, Micheal and Robin. All I need now is another clear night to get the colour.

Dave

[VigdisVZ]

Amazing job! Going to start unoffically call it the Yin and Yang nebula.

[Dave Smith]

Amazing job! Going to start unoffically call it the Yin and Yang nebula.

Dave

[Martin-Devon]

Dave I think you've really teased the best out of this - it's a great looking Bubble and is not an easy target - well done

[Dave Smith]

Thanks Martin. Much appreciated.

Dave

[sologuitarist61]

Excellent image Dave - very nice indeed

[Dave Smith]

Thank you Richard.

Dave

[Gina]

Very nice indeed

[Dave Smith]

Thanks Gina

Dave

[Tim]

This is a great area of the sky, and the bubble is an exceptional target, albeit a challenging one with that bright star within the bubble and the bright glowing edge of the bubble, and the very faint outer regions of nebulosity.

Dave, it might just be my tired astronomy eyes but the focus here looks a tad soft to me, is that a possibility? Almost like there was some murkiness in the air which has softened the overall effect a little and bloated the stars a smidge. It might be worth going through the subs individually and checking the FWHM figures for the stars from first image to the last, maybe with these colder nights the focus changed a little over the course of the session. Personally I have always found it difficult or impossible to focus perfectly on the moon with the effects of seeing.

I dont mean to put a downer on the image as it has lots of potential, but those blobby stars throughout are a bit of a concern, you might find that adding colour nothing quite matches up. An extra set of pinsharp focus Ha subs stacked and used as a reference could be combined with these for overall smoothness perhaps.

Cheers

Tim

[Dave Smith]

Thanks very much Tim for your comments. You are the first to comment on the softness of the stars and it is something that I did notice.

At the beginning of the run I did focus using a Bahtinov mask although didn't check again. I've had a look at the FWHM figures throughout the run and they are not good on any of the subs.

As far as I can see there are two possibilities that occur to me, firstly that the focus moved (accidental knock - I'm not aware of one) between focusing and starting the image run and secondly, the use of a focal reducer not designed for that scope. The FL102S is f8.8

Another thing that would not have helped was that the brighter stars are saturated even before stretching, but I don't think that is the main reason.

I've looked at the FWHM figures for other Ha images that I have done and they were much better.

I don't think I will repeat this one in the near future as there are too many other objects that I want to have a go at, e.g. I haven't attempted M42 since having my DSLR modded or getting a CCD camera.

However, your post has stressed to me how important it is to check focus repeatedly. Thank you for your help.

By the way, I have since taken OIII and combined it with the Ha. It can be seen here -> http://stargazerslounge.com/topic/169925-ngc7635-the-bubble-nebula-now-in-bicolour/

Dave