Recommendations for an OAG

[smr]

Hi, 

I'd like to buy an OAG but have no idea as to what to get. I've only just started reading up on OAG so I'm very new to this. 

Thanks for any advice.

[iapa]

I’d read / research some more first - always a good thing in this field. 

This may help you work out the initial soakings you will need based on OTA, imaging and guiding cameras.

My first, and very recent still unused, was a Celestron on OAG purely because I was intending to attach to a C8 SCT

[rickwayne]

I guess my first question would be "why do you want an OAG"? In other words, what are you trying to accomplish?

My second question would be "what limitations might your system have that would drive the choice?" For example, I have a field flattener/reducer with a 55mm backfocus. I can just get an OAG to reach focus with my filterwheel and ASI183MM behind it at the correct distance.

If it's well-designed, of course, an OAG's optical path from the front of the unit to the guide camera mounting will be the same length as the one straight through.

As you may know, one of the tricky bits in setting one up is getting the guide camera focused. Using my ZWO as an example, there is a setscrew to fix how far the stalk with the pickoff prism dives into the light cone, and another one that locks the camera as it slides up and down on the cone. It's a bit of a pain to focus by sliding a camera and then tightening the setscrew; one feature to look for is a helical focuser. In my case, there's no room in the optical path for such a thing.

Another issue is how the thing assembles. I wanted all threaded connections for my rig, but there is one fitting in the ZWO OAG that slides in and is locked by setscrews. Sort of like an eyepiece, except there are three screws and the wings of the fitting are angled a little bit so that the force of the setscrew tends to pull it forward (i.e., tighter). It's the "M48 adapter" in this image (the assembled OAG has the M42 adapter installed).

[Adam J]

On 03/02/2021 at 10:51, smr said:

Hi, 

I'd like to buy an OAG but have no idea as to what to get. I've only just started reading up on OAG so I'm very new to this. 

Thanks for any advice.

Personally I recommend that unless your imaging at over 1000mm focal length that you dont bother with an OAG as it will be more trouble than its worth.

Adam

[smr]

Thanks for the replies guys, I'll stay with my guidescope.