ASI120MC-S with Orion GoScope 80 - how to mount / focus?

hewhowatches

Hi, I'm an absolute beginner so please be gentle! I have an ASI120MC-S camera that I'm trying to get working with an Orion GoScope 80.

As the ASI120MC-S comes complete with a CCTV lens, getting it to work is no problem (works under Windows with AMcap and SharpCap, works with Fedora Linux using oacapture).

Once the CCTV lens is removed and replaced with the 1.25" nosepiece/telescope adaptor as per page 6 of the manual, you can see in the preview video window that there is no focus whatsoever. I assumed this was normal, and that focussing the camera would be done by the telescope itself. However, after replacing the eyepiece in the 90° star diagonal with the camera (and 1.25" adaptor), I seemingly can''t improve the focus at all.

Please can anyone tell me if I'm doing something daft, if the two pieces of kit are not compatible, or if I need an extra part to make them work together?

Many thanks! :)

firstc8

Sorry, we encountered an error while displaying this content. If you're a user, please try again later. If you're an administrator, take a look in your Flarum log files for more information.

hewhowatches

Thanks firstC8! I've tried removing the diagonal and fitting the 1.25" adaptor in its place but no joy, but can't seem to make it fit I'm afraid.

firstc8

HeWhoWatches wrote:
Thanks firstC8! I've tried removing the diagonal and fitting the 1.25" adaptor in its place but no joy, but can't seem to make it fit I'm afraid.

Just saw the pictures of your scope, looks like you need a "visual back" adapter to accept the 1.25" nosepiece.

hewhowatches

Ah, that makes sense, thanks! Bit tricky that, as the screw on design of the diagonal makes finding a compatible adapter difficult. There's a Celestron visual back, but it looks a little big I think. Looks like I'm not the only one with the problem though, as this clever gentleman made a video explaining how he made his own adaptor from plumbing bits.

As well as the YouTube video there are some powerpoint slides here.

Interesting points include:

Visual back uses non-standard thread size

With the diagonal in place, not enough in-travel

Without the diagonal in place, no way to attach to the rear threads

Telescope has an unusual focussing technique whereby the objective lens moves in and out

...all above my head as a beginner of course!

It also sounds like the adaptor has to be the right length, so possibly an off the shelf approach might not work (though if possible I'd certainly want to go that route)?

firstc8

If you can find the adapter, focusing should be easy, this type of scopes has long back focus range because the lens moves. But at very long focal length, a difficult one to image faint deep sky objects. So it will be limited to bright moon and planetary, and land objects.