Newbie 2nd try eta carinae nebula

[pkinchington]

My second try at eta carina I used an unmodified dslr to get some of the blue white colour near the centre but lost some of the red nebula cloud (no Ha?). Any suggestions to improve? Taken in Melbourne on the 20 June 2020.

[multiweb]

The left of the field is ok but there is something going on with the right side. You also seem to have something in the light path that causes diffraction spikes on your stars. The colours are good though.

[pkinchington]

Hi Marc, I just used one star alignment so the constellation was on the edge of my full frame image. I think that may have caused the issues on the rhs. I don't know what was causing the diffraction as I used my lens fully open at f2.8.
Cheers Peter (Kanga)

[jahnpahwa]

Hi Peter,

Are you on a tracking mount? What length exposure are you using here? Is this a single image or is it the result of a stack? If its a stack, I've seen similar spikes on my stars that look like diffraction spikes when i stack one blurred image into an otherwise decent group.

Looks like ironing one or two issues out will have a really nice image there!

JP

[pkinchington]

Hi Jahn,
I did a stack of 77 x 30s @ 200iso exposures and used a heq5 pro for tracking but I only aligned it using one star.
Cheers Kanga

[jahnpahwa]

Ah yep... perhaps worthwhile reviewing each frame once more to try to find and weed out any with star trails and re-stack? I've had plenty of bad images still achieve decent-ish scores in DSS once registered.

As for the stretched stars one side vs another, I have no experience there whatsoever sorry!

There is a big, excellent, recent thread here on aligning the HEQ5pro and similar mounts. It helped me and I think many others to sort out alignment gremlins... taking the time to really nail that down will pay dividends, no doubt! At your focal length there you should be able to knock out some pretty long exposures unguided.

You're close, mate.. its going to be great!

[multiweb]

ha ok it makes sense now. You should stop your lens maybe 2 stops down. If it's a heavy lens you might consider bracing/holding it with centering rings in front of your camera so it doesn't sag and stays square to the camera sensor. Try that first and see if it improves your field. Maybe the stars diffraction spikes will get better too with a few stops down.

[pkinchington]

Hi again Marq - I'll try stopping down. The camera is attached to my fast telephoto camera lens which has a tripod mount so the camera does not sag through bearing the weight of the lens.
Cheers Kanga

[pkinchington]

Ok Jahn - I'll have a look at the exposures I weeded out the ones that had clouds in them. If there is any wisp of cloud in any of the exposures could this lead to diffraction of stars in the final stacked image.
Cheers Kanga

[jahnpahwa]

Hi Kanga, I was thinking about star trails, so any frames where your star is a short line rather than a dot. This happens, even when well aligned. I think this might be what is happening with the longer spikes on the stars (though it may not be), and yes, I can see there are uniform, smaller spikes around the starts too, which may be the F-stop issue (again, which i have no experience with).

[multiweb]

can you post a pic of your rig?

[pkinchington]

Hi Marc,
I'll post it next cloudless night when I've dug up the gear again.
Basically I have used a guiding camera (on 50mm lens) on one side of a central bar (vixen mount?) and my telephoto lens with imaging dslr on the other. Both lenses are about 20cm from the centre of the Heq5 pro mount.
Cheers Kanga

[pkinchington]

My Rig

[multiweb]

I see. The lens is mounted on the side by side directly. Well the only points where it could flex are the camera attachement. If it's a bayonnette system they're known to have a little play and possibly the larger end of the lens. Does everything feel rigid?

I assume that's the guider on the other side?

[pkinchington]

Hi Marc,

Yes everything is rigid there is a little play in the lens to camera mount. If you think this is an issue I can eliminate any play with gaffa tape. And yes that is a guider on the other side.

Cheers Kanga

[pkinchington]

Hi Jahn,
I culled the lights down from 77 to 60 of the best. It made a substantial improvement. Please see image attached. I believe if I centre the eta carina nebula within my frame so that it is not at the edge and I introduce more data through narrow band work I could get a half decent image. A fair amount of wobble was introduced to some of the light sub frames when I walked around the deck on which the rig was set up (I need the elevation to see over the neighbours trees). I'll also save my pennies for an apo telescope.
Cheers Kanga (Peter).

[jahnpahwa]

Nice one, Kanga!
Yeah, that looks like it got rid of the longest of the spikes, one more step along the way :thumbsup::thumbsup:

[rustigsmed]

nice effort kanga, it looks as though you are zeroing in somewhat :thumbsup:

cheers

russ

[pkinchington]

Thanks for the encouragement Russell

[pkinchington]

Thanks for your guidance Jahn.