Off Axis Guiding

[Starcrazzy]

Im a bit confused about off axis guiding. I understand why it is needed for certain scopes, but how do you locate a guidestar. I have all sorts of trouble getting a good star with a dedicated guidscope, and I cant understand how one would obtain a good star when you can't move the scope, framing etc... I should mention im using a celestron stand alone guider. Does that make a difference? Could I use this guider with an OAG setup?

Cheers

[Merlin66 (Ken)]

Which guide scope are you currently using?
It could be the sensitivity or settings of your guider....
I've used a QHY5 on a ST80 and PHD for guiding..there's always a star to lock onto.
For OAG, yes it can be a bit of a fiddle, but once it's set up properly and used with a good guide camera (I use a Lodestar) it works 100%

[Poita (Peter)]

Okay, this might sound strange, and I'm sure people witll disagree, but I reckon if anyone is considering going OAG, then bite the bullet and get a lodestar or better. I tried so many combinations of other cameras and was convinced OAG was a bit of a joke. When I got a lodestar as a last ditch effort, suddenly off axis guiding just worked every time and was completely hassle free.

This is one of those areas where going cheap costs money. Buy a good guide camera and you will have it for life or until you break it. It is the best investment IMO.

[Starcrazzy]

Im using an orion short tube 80. The standalone system is great, you have to have reasonably bright stars to lock onto, but once its going it stays guiding.
The reason im asking is because im considering a GSO RC8, and ive read that a second guidscope is not the go with this type of setup. I would be perfectly happy to keep the shortube mounted to the GSO, but apparently it doesnt work/?..Anyone had any experience with this?

[Merlin66 (Ken)]

A guide scope will work with almost any telescope.
The issue/ problem is getting it securely and rigidly mounted onto the scope so that NOTHING moves....
With a Newt and other mirror scopes (SCT etc) there's always the possible problem that the mirror will shift/ slide/ flop during the exposure and still cause elongated star.
As an example....I initially used the ST80/QHY5 guide scope on a RIGID support bar on the C9.25 to guide my spectroscope...
I found even the slop of the 1.25" nosepiece on the guide camera gave problems and had to go to T thread adaptors...It worked very well, but for me on the C11 the beamsplitter/ guider is even better.

[Poita (Peter)]

I'd agree with everything Ken said, my experience with the C9.25 is almost exactly the same.
Meru has borrowed my lodestar and OAG, I believe he is trying it in an RC scope.

[Tandum (Robin)]

Some of them rotate around the imaging axis, they are not all fixed. So you can roll them around looking for a star. My problem with them is the space they take up. My mono camera and wheel already use up 50mm of back focus. You normally need some sort of flattener/reducer in front of that which normally wants 56mm to the sensor so the OAG needs to be really thin.

Really thin is expensive

[Poita (Peter)]

The SX is slim and is under $300