ngc7000 (part) in H-alpha. WIP

[ChrisLX200]

Working on a NB image of the 'Gulf of Mexico' region of ngc7000 - the North America Nebula. This is 6x20min subs in Ha. I'm not happy with the background noise level or the star shape but I'll be sorting that out as I go, even so it makes for a pleasing image of this interesting area of sky. A mosaic at this image scale would be nice but I'd need a heck of a lot more clear skies than I've been getting lately!

Hardware used is the usual NP127is + 0.8x reducer, Atik 490EX @ 1x1, Losamandy G11, TV Pronto+Lodestar.

ChrisH

[Epicycle]

Very nice, with a few more subs you should have a great image,

E.

[Kbramley]

Thats a solid start, the noise doesn't appear too bad to my eyes, looking forward to the full version

Keith

[swag72]

That's showing great detail and data so far Chris.

[Fay]

Looks very nice Chris. looks smooth to me, nice process

Fay 

[Gina]

I can't see anything wrong with that.  Great image and a great first step   Great detail

[ChrisLX200]

Thanks everyone!

I completed processing the SII data I captured on the same night so have thrown them together as a bi-colour. I have discovered (on advice from others) that the issue with star shapes is caused by the Lodestar interlaced frames - it is oscillating betweeen alternate frames at times. At least I know where to look for a fix. Anyway, the image:

ChrisH

[cosmicdonkey]

Wow that is amazing

[PhotoGav]

Looking great Chris.

Can you expand a little on the Lodestar issue please?

[ChrisLX200]

Looking great Chris.

Can you expand a little on the Lodestar issue please?

The Lodestar is an interlaced device, alternate lines from the full frame being used to produce sequential frames. Under some circumstances (not clearly defined to me) you can end up getting sequential frames that are displaced by one pixel because of this. I think I came across this issue earlier in the year when weird things were happening with DEC drift:

If you look at the image you will immediately see the DEC is being driven off at a steady rate, the PA was excellent here so that is not to blame. If you look at the star image you may notice it looks a bit like a close double star and what is happening is that the centroid of the lower 'part' is being chosen each time.

However, this is not the error I was getting when the above image was being taken but I think it's related, unfortuntately I don't have a screen grab of that to show you what happened. Essentially the first 20min sub would track perfectly, the guiding was then paused (by SGPro) while the frame was downloaded (to prevent saturating the USB bus which can cause PHD to crash) then re-started as soon as the download was complete. A dither command was then issued to PHD and guiding restarted. Immediately on restarting guiding the mount would oscillate in RA by approx +/- 1.5 arc-sec, the trace looks like a sawtooth and the star image changes from a nice round blob to a 'dual' image as seen in the image above. No amount of mucking about with guiding parameters will correct it although I could reduce it somewhat, but the point is the parameters are not to blame. The only way I found was to stop guiding manually then restart it again and eventually after a couple of attempts at this I would get back to the nice round star image again and guiding would be back to normal.

So the bottom line is that the interlaced readout is to blame and something (driver?) can get confused which frame it should be working with.

ChrisH

[PhotoGav]

Chris, that's a great reply, thank you for going into such detail. I see what you are on about, though am amazed that it is an issue when the Lodestar is 'the' guide camera - surely such problems shouldn't exist? When you find the answer, I shall be most interested as I am about to take delivery of a Lodestar as an upgrade to my QHY5-II guide camera!

Thanks.