The bubble nebula in H alpha, OIII and SII

[darditti]

I don't often post here, but I thought I would make an exception.

This is the only sort of thing you can image when there is a bright Moon in the sky and seeing is poor, as it was on the 15th.

I have imaged this object once before, from the very dark sky of Les Granges in France, but this result from London is better because of longer exposures and better tracking. (Since then Olly has invested in new equipment at Les Granges which I am sure would allow a far better result now than I could get then.)

The H alpha and SII emitting diffuse nebula behind the bubble shows pink in this rendering, whereas the planetary-nebula-like stellar wind of the bubble itself, giving more OIII, is yellow.

The C-11 fitted with a Meade focal reducer results in slight star coma at the corners of the field, but the effect is not too bad in my opinion. Technical details on image.

David

[barkis]

That is a real nice image David. You're spot on with the tracking.

It's odd that such a fine result can be obtained in spite of the conditions you say were prevailing.

Nice job indeed.

Ron.

[NickH]

Very nice David...

Hope you liked the book review...cracking read!

[Paxo]

That's an excellent image David, so glad you could pull something useful out of the gloom we have had recently.

Steve..

[661-pete]

Lovely image David, with superb colours despite the far-from-ideal conditions! (do poor seeing and LP actually enhance colours I wonder? I ask because of some of my own results). The bright 7th mag. star to left seems to have slightly off-centre diffusion disks, I wonder if there's any way you could fix that? Or is it just an effect of the coma you mentioned?

So glad you were able to rescue something and bag your bubble, after your disastrous mishap of the night before!

[darditti]

Yes, thanks very much for the book review Nick. I couldn't have expected a better one if I had paid for it (which I didn't).

The off-centre disks I think are diffraction disks caused by the Astronomik interference filters. I don't know if there is any way to stop this, or why they are off-centre. Maybe someone else knows.They always occur with these filters, I find, on any telescope, but sometimes they have been more symmetrical. It could be that collimation is at fault.

The "disastrous mishap" actually did occur during this imaging session, Windows updating itself and shutting the computer down. In fact I recovered it by starting again, and re-aligning on the same field as accurately as I could, and little damage was done, though an hour of potential imaging time was lost.

David

[barkis]

I trust you have modified the Windows Auto Update settings David.

Almost disasterous for you that.

Ron.

[Paxo]

The off-centre disks I think are diffraction disks caused by the Astronomik interference filters. I don't know if there is any way to stop this, or why they are off-centre. Maybe someone else knows.They always occur with these filters, I find, on any telescope, but sometimes they have been more symmetrical. It could be that collimation is at fault.

David

MartinB (in another post) mentioned these off centre halo's are caused by reflections off the narrowband filters and imaging chip which can be eliminated by adjusting the positioning of the filters in the optical train (use of a spacer for example).

Steve..

[RobH]

Nice work David, didn't know you did deep sky stuff too

I too get the same discs, especially with my NB filters.

Yes, you can alter them by changing the distsnce from the chip, but in practice, if you're using a filter wheel, it's not that easy!

Cheers

Rob

[darditti]

Yes, the theory that the rings are due to reflections between the filter and the chip (or, more likely, the optical window in front of the chip) makes sense, as the Astronomik NB filters are very reflective.

The rig I used for this image is shown in the photo below. The filter wheel is right in front of the camera, with a T-spacer between it and the Celestron radial guider. If I put the spacer between the wheel and the camera, the right-angled part of the radial guider would tend to collide with the filter wheel. However, I will try putting in spacers on both sides of the FW to see the effect, though that will make the imaging train even longer, and take the camera further from the focal reducer hence increasing the image scale.

David