C9.25 and a guide scope

[iamzoso60]

My current set up is a Celestron 9.25 on a CG5-GT head, mounted on a fixed pier, in a Skyshed POD.

I am looking at fitting a guide scope on the C9.25, probably a ST80 and was wondering which would be the best way to "mate" the two together.

Has anyone done anything similar?

[Mr Spock]

I've got an 80ED attached to mine with an ADM mini dovetail and 125mm rings. Works fine.

You will need an extra 5kg counterweight though and I would recommend a stronger dovetail for the scope/mount interface - the vixen I have isn't really solid enough.

[brantuk]

You can usually fix some appropriate sized guide scope rings on top of the main tube rings to piggy back an ST80. But you will get some amount of flexure.

Another solution worth consideration would be to use an off axis guider (oag) instead - the Celestron one rotates 140 degrees to find a guide star.

[Merlin66]

I have the same ADM minirail etc for my ST80/ QHY5 guide set-up and use the Losmandy wider dovetail on my C9.25

[ollypenrice]

The CG5 is already marginal, in imaging terms, for the 9.25. I'd second Brantuk's suggestion of an OAG to cut down on weight. Besides, many SCT imagers end up oprting for these since guiding at longer FLs is critical.

Olly

[iamzoso60]

Thanks for the quick replies, but where would I attach scope rings on top of the tube? Pics would help, if possible.

[ollypenrice]

There a little black dome head allen bolts around the front and rear of the OTA, I think. These are designed to take accessories.

Olly

[fatwoul]

How would an OAG be on a scope like a 925, though? I only ask because my OAG usually only offers (at most) half a dozen stars in any given field, and that's on an f/5.3 scope. Would an f/10 scope not be a bit dark for an OAG?

[ollypenrice]

Very likely but you'd not want to do too much at f10, surely?

Olly

[riklaunim]

OAGs and "dark" scopes are a nice pair. I was/I'm using Celestron Radial Guider with C8/C11 now and it does work - I can do 600-900 sec exposures (with DSI III Pro + reducer). Sometimes it's hard to find a guide star but if you have one - the guiding must work (and if it doesn't then something is wrong, badly - like guiding settings, scope balance, very very fast drift, poor gude cam...)

I'm also testing finder-guide-scope: http://oi51.tinypic.com/29ftp4j.jpg - first try showed it can "work" (NGC7009 at 0,49 arcsec/pix test) but still I don't have any data for 600-900 sec with a reducer on a reasonable resolution The advantage is that it sees a lot of stars and the target in a big FOV

[Merlin66]

We used OAG for twenty years on various SCT's. Most, if not all the film imaging we did at f10 and with reducers at f6.3 used OAG. Never any real problems. Things seem to have changed over the years.....