Bubble Nebula high-res

[darditti]

Having had some success on this object recently with a C11, I thought I would go for it with the C14. This is still a "work in progress" and may remain so, since I have been waiting for about a month with the camera on the scope trying to get suitable conditions. I got several short interrupted sessions that were not compatible, the best was 75 minutes on the 3rd, the longest clear interval I have had in that time, from which this image has been made. I have not got a suitable flat field either. I was hoping for more (and other wavebands) but I am posting it now in despair at the conditions.

It was actually quite windy on the 3rd. The quality of the tracking in an open-roof observatory at 2450mm FL is a tribute to the AP1200 mount.

David

[Psychobilly]

Cracking image David

Hope you dont mind me asking is the colimation out slightly on the scope - i'm wondering becasue of the patterns round the brighter stars...

Billy...

[darditti]

Could be. This is a problem I have been getting with this set-up. The patterns are due to reflections between the filter and the camera (we concluded when I asked about this on here before). They always occur, but I should try tweaking the collimation to see if it changes them. Clear skies have been so brief I haven't dared try.

David

[Psychobilly]

So are they caused by angular mis-alignment between the filter and other optical components...

Very interested because I sometimes get somethign similar when i image trough my CPC800..

I haven't gone back through forum posts i'll have to search out the thread.

Billy...

p.s. I know what you mean about collimation - I havent had a chance to tweak mine back in properly since changing to "bob's knobs"

[anthony]

Stunning shot David Very smooth and delightful detail.

I fancy that most of these offset halos are due to the filter/filter wheel. Before I had a filter wheel the filter went into the camera nosepiece and so sat nice and true to the optical train. My halos were there but nice and concentric with no offset from the centre. I reckon that due to how the filter wheel is designed so that it can rotate the actual filter itself is possibly sitting at a slight angle to the optical path creating the pattern we see in the halos.

PS did I say - stunning image. Fair old focal length there. Give your mount a pat on the back

Anthony

[darditti]

Useful thoughts there. The filter wheel I used is the Astro Engineering Imagers Filter Wheel which in fact is not the best engineered wheel (and not made any more, though the ScopeTekniks one looks very similar so is probably from the same factory). In fact I had to modify the wheel with spacing washers to allow it to take thicker filters. All of this means that the asymmetry could indeed be due to the wheel. I have the ATiK wheel as well, which is better made, so I could try that.

My suspicion also about the Artemis 285 camera is that the front window is not anti-reflection coated, which could be a big part of the problem. If the problem is indeed reflection between this window and the filter, telescope collimation would have little or no effect on the shape of the haloes. I think this is the case, as I have had the asymmetric haloes when imaging with a refractor as well.

David

[centroid]

A nice result indeed!!

I know only too well about RoR obsy's, and how the wind can make life difficult when imaging, hence converting my RoR to a rotating turret arrangement.

It would seem that your AP mount, is a major asset under windy conditions.

Dave

[barkis]

I know how you must feel about weather causing delays. It is rife throughout the imaging fraternity in the UK that's for sure. All the imagers on SGL will testify to that, although I am not involved yet.

It has a great start, and I hope you get the necessary data to get it the way you want it, and with processing it will be excellent I'm sure.

Ron.

[Paxo]

Excellent image David. There are several theories going about on this forum alone regarding the halo's. It would appear that the Astrodon 6nm filters have anti reflective coatings limiting this problem, and looking at the images shown on the forum that would appear to be the case.

Tony (whippy) has read somewhere that there is a small leakage of IR through the Astronomic filters (13nm) which is due to be tested next clear spell.

I'm sure we will come to the bottom of it very soon.

Steve..

[Paxo]

David, Billy, take a look at this article from Astrodon:

http://www.astrodon.com/articles_faq/articles_faq/press_release:391,355,49

Steve..

[Psychobilly]

Thanks steve

Billy..

[darditti]

Interesting article. It confirms that haloes are due to internal reflections near the camera and that there are several possible sources. However, we observe that in narrowband images like this the haloes are very strong. This seems to prove they are due to reflection either between the filter and the camera window, or the filter and the camera chip. I don't find strong haloes like this with broadband filters, so I think the filters are definitely involved. There is probably an IR leak in the Astronomik H alpha filter, there is in most filters, but I don't think that's much to do with it. The other factor, as the article demonstrates, is the camera to filter distance. As this increases the haloes get bigger and weaker. They would be less noticeable if the distance were increased. I could do this if I could find another short (approx. 10mm) T-spacer to place between my filter wheel and camera, so then I could have short spacers on both sides of the wheel rather than one long one above the wheel. However, it looks like whatever one does, at long enough exposures the haloes will show up. They would be aesthetically better, however, if they were symmetrical.

I would be interested, Dave, to find out more about how you converted your roll-off to a turret observatory. They are such different structures I would have thought that would involve more or less a complete rebuild - but if you found a cleaver way to do it, I would be interested to see it!

The AP1200 mount is, indeed, worth more than its weight in aluminium and stainless steel. I would get the new AP3600 if I could afford it!

David

David