Coma cause ?

[Davey-T]

Been messing about trying to get a decent image out of this Sharpstar 150HNT scope, I think it's pretty well collimated but has coma across the whole image in the same direction, took this single 10sec' shot of the double cluster last night.

It has a dedicated built in coma corrector reducer all connections screwed together.

Focuser has tilt adjustment, could tilted focuser cause this effect ?

Dave

[Stub Mandrel]

Could also be collimation/alignment as well as not enough spacing for the corrector.

Download the trial of CCD inspector and see what it says. Of course the risk is you will want to buy it...

[Davey-T]

22 minutes ago, Stub Mandrel said:

not enough spacing for the corrector.

Can't do anything about that it's fixed.

Dave

[Peter Drew]

Coma across the whole field is usually caused by a tilt in the system or collimation, more likely the former.  Incorrect spacings usually show as radial coma.       🙂 

[Skipper Billy]

CCD Inspector suggests that your focus is good and that you have a fairly flat image suggesting that your spacing is good.

It also reports that the likely problem is straightforward collimation.

 

[Davey-T]

19 minutes ago, Skipper Billy said:

It also reports that the likely problem is straightforward collimation.

Thanks David, unfortunately collimating this scope is anything but straightforward, a bit like your RC, I've lashed out a few hundred quid on a HG,  guaranteed to be to be collimated itself laser, plus grid attachment for fast scopes and spent ages getting it as close as I can, not helped by the abysmal Sharpstar QC.

There doesn't appear to be enough forward movement in the secondary to get it centred under the focuser which isn't helping matters, may have to take a hacksaw to it 😂 

Guess I'll have to spend more money on CCD inspector now, suppose it will come in handy for all my other gear.

Dave

Edited July 7, 2020 by Davey-T

[Skipper Billy]

Aaaaargh - you just spoiled my day by mentioning the RC that I had !!!! The very mention makes my blood run cold 😉 

Happy to run images through CCD for you as often as you wish - just PM me and I will give you my email address to save cluttering up the forum.

Good luck!

David

[Davey-T]

Oops sorry David, this thing is getting to be the same way, that image was taken with 60Da, I had a plan to use it with a ZWO ASI2600mc, also purchased especially for it, for fast image captures at a dark site but as we know best laid plans aft gang awry.

It arrived uncollimated and I haven't achieved a single image with it yet. I have a thread somewhere documenting the trials and tribulations of it.

Thankyou for your kind offer I will be glad of all the help I can get, no doubt interpreting CCD inspector findings isn't as straight forwards as the makers claim.

Think I should cut my losses and buy a Tak' Epsilon 😂

Dave