Guidescope choices

Hi all,

Eventually I will be getting more involved in astrophotography and was wondering about choices for guidescopes, good, bad or otherwise.

I see a lot of people chroose 80mm refractors for small to med size setups and it goes up the aperture scale from there. Is there anything intrinsically wrong with using a small Mak-Cass (say Orion's 90mm Mak)? Seems small and light enough with a good focal length (?)

Comments welcome.

Marc B.

Mark,
The problem with any guide scope can be the focal length and f-ratio. The ratio and length and camera should come close to matching pixel size of the imaging camera. Too small a pixel size in the guide camera and seeing can cause the guiding to hunt down the star as the atmosphere causes it to seemingly move. This results in quick guide changes ,which is not good.
The quality of the guide scope does not have to be that good.
Light weight is always a plus.
A focal reducer can be used to bring down the focal length of the guide scope, I use a .5 on my 80mm f/11.3 guide scope.
Rigid mounting for the guide scope is a must, flexure can ruin your night by causing drift.

Mark, I'm sure you'll get a lot of answers... (I hope)...
If you are "manually guiding", then getting/using a longer focal length scope than your imaging scope is a must... as you must catch the star movement before your imaging scope does...

If you are autoguiding, then your guidescope does not have to be longer than you imaging scope, actually, it will still be ok if you guiding scope is same or even a little shorter (in f/l) than your imaging scope, as software & cameras will handle this area quite well.

The problem with using a MAK as your guidescope is that the FOV is VERY limited, and your chances of finding a guide star in the area will be a lot tougher...

Of course, this is just my humble opinion... 8)