Melotte 15 (Hubble Palette)

[Carole]

This image was more an experiment with a Newtonian I bought in March and not used it yet.  Its a Skywatcher 150P (not the PDS version) so was not even sure I could get focus, I had been planning to get a SW130PDS, but as this came along for half the price, I thought it was worth a punt. 

I definitely think this needs a dark site as it is quite noisy, but am posting up for feedback and advice.

a) I had a coma corrector in place which I bought with the scope, but I think it is probably designed for a DSLR and have no idea what the spacing should be with a CCD camera, there does seem to be a bit of coma, esp top right. 
b) Some of the stars look a little flattened at the top, not being experienced with a Newtonian, could this be something to do with the focusser?

Well at least I got myself out and imaging for the first time from home for about 6 months, but running out of targets that are suitable from Bromley.  There is a definite difference between data done at home and a dark site even with narrowband.

No idea what this is supposed to look like. 

Ha 9 x 900 secs
Oiii & Sii each 7 x 450 secs binned
Atik 314L & SW 150P

[Carole]

Well I was hoping for some sort of feedback.  I know this is not the greatest image in the world, but it was the technical issues I wanted advice on.

I seem to have found an answer to the coma question myself and it's a personal gaff.

I have just de-rigged ready for Kelling, and found the extra "nosepiece" I had put on the end had a lens in it  !!!!  I had put on my field flattener instead of just a spacer/extender, so there was double flattening going on. (Hmm, the trouble with doing things in the dark).

I am probably not going to stay with this coma corrector anyway as it is not a reducing type.

However would still like some feedback on the major stars which seem flattened on one side, is this something to do with the focusser?  I know many of you don't use Newtonians, so maybe I have to take my question elsewhere.

Carole

[MarkS]

The stars are flattened on one side and they have a diffraction spike running through the flat part.  The flat part is difficult to explain but the diffraction spike will be caused by the edge of some component or a wire interrupting the cone of light.  Maybe that also explains the flat bit, I don't know.

Do you see it on all 3 filters?

Mark

[Carole]

I am on holiday ATM but mark this is a  Newtonian so is supposed to have spikes. 

[MarkS]

I am on holiday ATM but mark this is a  Newtonian so is supposed to have spikes.

The spike in one direction is far stronger than the spike in the other.
To diagnose this I would:
1) Check the collimation
2) Take some defocused images of a star - defocused inwards and outwards and with successive amounts of defocus
The results might give some clue as to what is going on.

Mark