AM5 and long FLs

[pmrid (Peter)]

The standard blurb with the AM5 makes the point that it is not suited for use on focal lengths beyond 1000mm. I have wondered about that.

No doubt, the longer the optical tube, the more it affects the moment of inertia and that would have an impact on the drive motors. But so far, I have not encountered any measurable effect of using, say, an 8 inch Newtonian on mine. I even put a C11 at 2800mm on it once (with a CW of course) and the only problem I had was with collimation - not slewing or tracking. It seems likely that the issue is with the length of the OTA rather than the FL - as in SCT scopes etc.

Any thoughts?

[ronson]

When you say suitable, do you mean for visual or imaging?

For imaging, both the weight and focal length of the system play role when choosing a suitable mount. AM5 punches above its weight for the lightweight and compact size it has, but it has its limit. And the mount's tracking precision needs to be matched to the imaging resolution.

[Nikolas (Nik)]

Originally Posted by pmrid

The standard blurb with the AM5 makes the point that it is not suited for use on focal lengths beyond 1000mm. I have wondered about that.

No doubt, the longer the optical tube, the more it affects the moment of inertia and that would have an impact on the drive motors. But so far, I have not encountered any measurable effect of using, say, an 8 inch Newtonian on mine. I even put a C11 at 2800mm on it once (with a CW of course) and the only problem I had was with collimation - not slewing or tracking. It seems likely that the issue is with the length of the OTA rather than the FL - as in SCT scopes etc.

Any thoughts?

People have used it successfully with SCT's no issue Youtube and the am5 facebook forums has plenty of examples

[Nikolas (Nik)]

Originally Posted by pmrid

The standard blurb with the AM5 makes the point that it is not suited for use on focal lengths beyond 1000mm. I have wondered about that.

No doubt, the longer the optical tube, the more it affects the moment of inertia and that would have an impact on the drive motors. But so far, I have not encountered any measurable effect of using, say, an 8 inch Newtonian on mine. I even put a C11 at 2800mm on it once (with a CW of course) and the only problem I had was with collimation - not slewing or tracking. It seems likely that the issue is with the length of the OTA rather than the FL - as in SCT scopes etc.

Any thoughts?

People have used it successfully with SCT's no issue Youtube and the am5 facebook forums has plenty of examples

[pmrid (Peter)]

Originally Posted by ronson

When you say suitable, do you mean for visual or imaging?

For imaging, both the weight and focal length of the system play role when choosing a suitable mount. AM5 punches above its weight for the lightweight and compact size it has, but it has its limit. And the mount's tracking precision needs to be matched to the imaging resolution.

Hi Ronson,
I had imaging in mind since that is my primary (only) interest. Obviously, visual use would be more forgiving of a bit of OTA wobble.

I'm tossing up deciding which mount to take to Astrofest up here next week - and at the moment, I am leaning towards taking a heavier mount (a EQ6-R with belt drive) so I can use both my 8 inch Newtonian F5 and my StarpStar94EDPH refractor - a F5.5 scope that does lovely mid-range work with a 0.8 reducer/flattener.

I'm feeling a bit guilty about not taking my AM5 though.