Omega Centauri NGC 5139

[wayne anderson (Wayne)]

5x3 min subs iso1600
20x30sec subs iso1600
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30mins total

Meade 12inch LX200GPS (f6.3, alt/az setup, de-rotated)
Sony Nex 5n DSLR (full spectrum modified)
Processed with DeepSkyStacker and Startools

I noticed my zero shift focuser was not centered and angled properly causing the camera to be tilted and giving egg shaped stars so i laser aligned the focuser and gained good results.

However on the very extreme edge of field stars are triangular and show a radial pattern with flat edge facing the centre of image and point facing away, i am using a Meade f6.3 field flattener/reducer, could this be over or under correction of the field flattener and be fixed by adjusting spacing, or is this something else, any thoughts on this?

Thanks, Wayne.

[Atmos (Colin)]

You've done well and it is nicely resolved!

I think the issue in the corners is to do with the corrected circle of the 0.63x reducer. You camera sensor may be larger than what the reducer is designed to correct for. Just means that you may need to crop out the edges.

It could also be that the spacing is a little off as you suggest. Checking the specs on the reduced and/or trial and error on the spacing will give you an answer

[wayne anderson (Wayne)]

Thanks Colin, yes cropping the images should be ok for now as its only a small amount at the edges, i might try adjustments to spacing later.

[Cimitar (Evan)]

Originally Posted by wayne anderson

5x3 min subs iso1600
I noticed my zero shift focuser was not centered and angled properly causing the camera to be tilted and giving egg shaped stars so i laser aligned the focuser and gained good results.

Hi Wayne, great effort on the glob! Nicely resolved and I can't help but be drawn to looking at the core, which is what naturally happens under the night sky.

I was wondering if you could please elaborate a bit more on how you detected the focuser not being centered/angled correctly and the steps you used to correct it? I too have a Meade (mine's an 8" LX200 ACF, with zero shift focuser) and I also get eggy stars occasionally. I'd like to assess my focuser but I'm not sure where to start?

Cheers, Evan

[wayne anderson (Wayne)]

Thanks Evan, at first i thought my focuser was aligned well but that was clearly not the case the scope optics were collimated very well using the defocused star method and optically seemed very good.

While using a Glatter collimator i noticed with the holographic attachment the secondary shadow was slightly out of alignment with the grid pattern and also using the standard dot the laser dot returning from the secondary mirror to the collimator was slightly out of alignment.

With the laser collimator in place and turned on in the focuser i loosened the 3 hex screws that hold the focuser to the visual back of the scope and with a lot of fine tuning adjustments tightened the 3 of them so as to have the returning laser dot at the very centre of the collimator, i also checked with the holigraphic attachment attached and fine tuned the 3 screws so the secondary shadow was aligned very well at the centre of the grid.

I then checked again using the defocused star method only a very very small adjustment was needed, then i checked again using the laser collimator, now finally the scope has a straight optical path and very good Collimation.

Hope this helps you with your scope.

[jsmoraes (Jorge)]

Congratulations Wayne, you did a very beatutiful and resolved image of this cluster.
You managed very well the capture to take wonderful look of cluster core.
The core of this cluster is very impressive. And is difficult to catch the stars in it.

Like some people, I think it can be a remanescent core of a dwarf galaxy.

note:
I work with newtonian 12" and Canon 1100D, and did similar photos. I can say that we got the best resolution performance from our 12" scopes.

You have some triangle distortion at periphery, I have coma distortion. I use coma corrector, but I can't have the correct distance because of OAG and filter wheel attached.
By now, I am having similar issue about the alignment of secondary mirror,focuser and camera, with oval distortion of the stars shape. Unhappily I didn't get solution yet.

As few mates do Omega with this high image scale, you can take a look of my photos at:
http://astronomia-e-astrofotos.10697...us-td2160.html and http://astronomia-e-astrofotos.10697...14-td1572.html

[Cimitar (Evan)]

Thanks Wayne, really appreciate the description. I'll take a closer look at my scope
Cheers, Evan

[wayne anderson (Wayne)]

Thanks Jorge, i looked at your photos of Omega Centauri Cluster, they look very good and well resolved to the core.