Guiding : Focal length

[Earl]

I currently use an OAG so my guide focal lenght is identical to my imaging focal length 387mm  I get perfect stars upto 15mins, after that my PA is the weakpoint and eggyiness creeps in.

Im looking at adding a long focal length scope in and run both it will be 1600mm

Will I need to consider guiding with an OAG on the longer focal lenght or can I get away with the exsiting oag setup.

[swag72]

I can't imagine why you'd have any issues with an OAG at the longer focal length. You know that I will be looking at a focal length of 1600mm also soon, and feel that as I was guiding fine at 2.3m before the shorter focal length should be a breeze!

[Bukko]

Hi, Earl,

I am not sure what mount you are using, as I don't use a Celestron. I took a look on FLO at their mounts; there is the CGE Pro and CGEM's. Assuming you have a good Polar Alignment, the OAG should be able to hold a guide star pretty much all night. If you are out, then there will be some field rotation which might be your eggy stars ?

As a reference for you, I OAG on the SW NEQ6 at 1200mm and have no issue with loss of guide. However, mine is mounted on a pier, on a couple of tons of concrete and finely PA'd.

I do see some guide errors at 1200mm, so I would say I am probably on the limit for the NEQ6. If yours is the CGE Pro, then you are likely OK at 1600mm, assuming it is nicely set up.

Much smaller then I would give due consideration to the mount.

Good luck and hope this helps.

Gordon.

[Earl]

sorry to be clearer.

my qsi with oag is on my reduced fsq so at 387mm

i want to image on this and also a 8"rc at 1600mm at the same time.

will i be able to guide still uing the fsq or need to guide on the rc

[wuthton]

Surely you'll need the OAG on the rc as even the tiniest amount of flexure will show up but at 387 it won't be a problem.