do my guide stars look right ?

[red dwalf]

been using the ZWO ASI 120mm camera for guiding and all has been going well but i`m starting to think that my guide stars don`t look right, i`ve tried my best to get the best focus but the guide stars all seem to have little diffraction spikes rather than being nice and round. 

what do you think and any help in getting them round or does it not matter too much.

 

[+Graham]

I have always found PHD works better when the guide stars are slightly out of focus.

[+RonC]

Agree with Graham, but if PHD is tracking OK then 'if it an't broke then don't fix it!' My stars (using a QHY5) look similar to yours but no spikes.

 

Cheers

Ron 

 

(must try EQmod sometime!)

[red dwalf]

i have been told that it works better with slightly out of focus stars, but this was about the best i could get, ok it`s only a cheap st80 and a plastic diagonal so i suppose i shouldn`t be expecting too much from it.

[red dwalf]

EQmod works great with it Ron, saves using a cable or two also which is good as my cables are starting to look like a nest

[+Graham]

i have been told that it works better with slightly out of focus stars, but this was about the best i could get, ok it`s only a cheap st80 and a plastic diagonal so i suppose i shouldn`t be expecting too much from it.

Rob I would ditch the diag and put a spacer in there instead.

[red dwalf]

might try that method instead Graham,  

[Guest Kheldar]

I guide on sea gull shaped stars - take what you will from that

[glider]

Could be the diffraction spikes are real. The ST80 can appear to have spikes because;

 

.......The primary optics are pinched, looks more like a nuclear radiation symbol.

.......The ends of some screw threads encroach into the light cone going through the OTA.

 

Dion on Astronomy Shed has a write up for using shorter screws and blackening the screw threads.

[red dwalf]

Thanks guys,

I'll take a look at that Noel while the weather's bad.

[Guest peter shah]

^{you need to keep your guide exposures no less than 3s, longer if your mount will allow it, any less and you will chase the seeing causing poor guide corrections. My guider will run between 3 and 6s and I do 1800s exposure, my guiding is very reliable, the only time I will scrap a frame is if the guide star fades through cloud for too long. The idea is the longer exposure averages out the poor seeing. I would also select a guide star that isn't so saturated so the software can get more of an accurate centroid. If its too bright it will cause the guider to bounce backward and forward again causing false corrections.}

Edited June 6, 2014 by peter shah

[red dwalf]

i`ll try that, thanks Peter,

i`ve been setting the exposure to 1 second and have usually been choosing a bright start if there is one

[+RonC]

That's worth knowing Peter, I use 1.5-2 secs, never tried any longer but like Rob I'll give it try too!

[Guest AstroBilly]

Plus 1 for slightly out of focus guide stars