M13 - No Guide Stars

[gnomus]

I've been trying to use my new CCD camera.  I've now tried 3 nights, and have struck out 3 times.  So far, I've accumulated a total of two usable frames, and even these are not all that good.  Probably all of the issues I have had have been down to my own stupidity.  I've been able to work most of these things out (I think) and so won't bore you with all of my travails.  One issue I have not been able to solve, however, relates to guiding.

I have now had 3 nights of trying to image M13.  (This seemed to be a recommended 'summer' object.)  Each night I have been out I have had a great deal of difficulty finding any stars at all to guide with.  I use a ZWO ASI120MM-S as a guide camera.  In PHD2 (2.5.0) I have selected the Windows WDM-Style Camera.  (There is a ZWO camera option, but this greys out the Camera control box in PHD2.)  I set the exposure value to 3 seconds (initially).  Gain was set at 70.  On night one I tried to use my ST80 for guiding.  I could see no stars at all in the PHD window.  I tried various settings for exposure and gain, but ... nothing.  On night 2, I went back to the 9x50 finderscope for guiding.  This time there were only two stars.  I asked PHD to autoselect a star.  This worked for ~10 minutes until the clouds rolled in.  On night 3, I tried the ST80 again, but could find no stars.

I have the ST80 fixed to the top of my ED80.  I cannot figure out what is ado.  Is it that there is a paucity of suitable stars around M13?  Is it because we are not getting adequate darkness (I'm generally giving up by midnight)?

Any thoughts?

Would there be a more suitable target for me to have a go at at this time of year? 

[Ant]

I suspect it's a focus issue.

You will almost certainly need the diagonal, or some other form of extender to reach focus with an ST80.

Best bit of advice I can office is wait till the moons around and double check that you can reach focus as you have it set up.

The ST80 is a F5 scope, with a lovely big FOV, so you should have plenty of stars available.

Ant

[gnomus]

I suspect it's a focus issue.

You will almost certainly need the diagonal, or some other form of extender to reach focus with an ST80.

Best bit of advice I can office is wait till the moons around and double check that you can reach focus as you have it set up.

The ST80 is a F5 scope, with a lovely big FOV, so you should have plenty of stars available.

Ant

Thanks for replying. I should have mentioned that I need to use a 2" extender with the ZWO/ST80 combo to achieve focus. Furthermore, when setting up (in the twilight) I make sure that the ZWO is focussed on a distant object.

[davedownsouth]

Wait until the moon is up in a night or twos time and use it to get both the scope and guide camera into focus at the same time, this is how I sorted out focus with my OAG. With regards targets with suitable guide stars (I found problems finding a suitable guide star when I tried doing M13 as well), try an object in or around the Milky Way / Summer Triangle. How about something in Cygnus; if you can't get a decent guide star there, something is definitely up

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[gnomus]

Wait until the moon is up in a night or twos time and use it to get both the scope and guide camera into focus at the same time, this is how I sorted out focus with my OAG. With regards targets with suitable guide stars (I found problems finding a suitable guide star when I tried doing M13 as well), try an object in or around the Milky Way / Summer Triangle. How about something in Cygnus; if you can't get a decent guide star there, something is definitely up

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I think I will try different object.  Regarding Cygnus, what would you reckon to either the veil nebula or the Pelican nebula, at this time of year?  I only have LRGB filters at the moment, and am looking for something relatively easy.   

[Davey-T]

Did you take a dark in PHD sometimes helps stars to appear where non were before.

Dave

[gnomus]

Did you take a dark in PHD sometimes helps stars to appear where non were before.

Dave

Yes. I built a dark library ... Or rather a bad pixel map.

[gnomus]

Wait until the moon is up in a night or twos time and use it to get both the scope and guide camera into focus at the same time, this is how I sorted out focus with my OAG. With regards targets with suitable guide stars (I found problems finding a suitable guide star when I tried doing M13 as well), try an object in or around the Milky Way / Summer Triangle. How about something in Cygnus; if you can't get a decent guide star there, something is definitely up

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Thanks again for the suggestion to change targets.  I pointed everything (as best I could) at the Pelican nebula last night.  There were loads of suitable stars (I let PHD2 AutoSelect one).  The calibration routine was swift.  PHD2 guided reasonably well throughout 49 exposures without a single hiccough.  It was reassuring to have a reasonably successful night after three failures in a row.  

I'll have another go at M13 once I've got a bit more experience.