Is my Star Test okay? Also I have a ghost!

[Stargazer33]

Hi, I recently purchased a Celestron 8" SCT and it took me a while to pluck up the courage to collimate it. The other night I hooked up the web cam and did a star test with this result.

My question is, does it look okay? I keep worrying that the scope isn't collimated properly (my last scope was a Mak so no real need to collimate) and I wonder if I am getting the best image that I can in the eyepiece.

Also, I had a ghost appear on the laptop screen when I tried to focus on a star. The ghosting slowly appeared as I got nearer to focus. Image below:

Could this be dew on the corrector plate causing the image to ghost? I don't remember checking if it happened with an eyepiece as It wasn't a very nice night and my imaging attempts weren't really working out so I think I just packed up. I have just come across the image whilst transfering some files from the laptop to the PC for processing. I haven't had this on any of my visual observing nights and this is the first time that I have had anything like this with the webcam. I'm pretty sure I was using my home made dew shield that night, but there was a bit of dew forming on the corrector plate towards the centre, around the secondary housing.

Any advice/suggestions would be most appreciated!

Bryan

[x6gas]

The first image looks like you have the scope quite a way out of focus and I'm guessing this is without a barlow? Collimation looks OK on this evidence but the real test is when you crank up the magnification...

Can't help with the 'ghost'. Odd that the star is out of focus but the ghost looks closer to focus...

[DirkSteele]

If you are concerned about the collimation of your SCT there are other tools available to you that can help. Search on the SGL for "Duncan Mask." I and several other SGL members have posted about it including a link with instructions on how to make (just need some cardboard and scissors) and use it. The template in the link is for an 8" scope.

Clear skies,

Matthew

[Stargazer33]

The first image looks like you have the scope quite a way out of focus and I'm guessing this is without a barlow? Collimation looks OK on this evidence but the real test is when you crank up the magnification...

Can't help with the 'ghost'. Odd that the star is out of focus but the ghost looks closer to focus...

Thanks x6gas! I will try again with my 2.5x barlow and see how the star test performs then.

If you are concerned about the collimation of your SCT there are other tools available to you that can help. Search on the SGL for "Duncan Mask." I and several other SGL members have posted about it including a link with instructions on how to make (just need some cardboard and scissors) and use it. The template in the link is for an 8" scope.

Thanks Matthew! I will have a look at that post and give it a try. I did make my own Bahtinov mask for my 4" Mak from an old DVD case. I thought the black plastic would last a bit longer than cardboard, but DVD cases are not big enough to make one for my C8! I'll get some thick black card from my local arts supply shop and try making one of each.

Thanks again for the help.

Bryan

[x6gas]

I made a Duncan mask for my 11" SCT out of a plastic pizza tray.

The pizza was tasty too .

[Stargazer33]

Pizza Hut here I come! "Other fast food outlets are available!"

[x6gas]

Pizza Hut here I come! "Other fast food outlets are available!"

Actually it was from Tescos! Pepperoni IIRC... Mmmm could eat one now!