New gear arriving - OAG Question

[Muzfox]

Well it's been 3 months of clouds so I've been spending my time saving and shopping and am finally going mono after 3 years. I've just received my new camera, 2600mm Pro and Antlia 3nm Filters. I've also upgraded my scope which arrives today, the Askar 107 PHQ. I'm very interested to see the performance first hand of this system.

I currently use guidescope+cam but am thinking about adding an OAG to this system. The rear connection of the scope takes a variety of options down to 48mm. With the 2600mm and 36mm 7 position filterwheel am I correct in thinking that the ZWO OAG-L is the right one to use for the larger aperture? I have a concern that it appears the OAG-L doesn't allow itself to be rotated so you can't locate guide stars separate to framing of camera? The scope itself allows full 360 degree rotation of the image train.

Anyone with experience of the OAG-L?

Murray

[multiweb]

Nice scope Murray. :thumbsup: TBH I don't think you'll ever have any issues finding a guide star at ~700mm FL with an OAG. Even if you have to slightly offset your fov it will have a very minimal impact on your framing. That and the fact your refactor is 4 elements which I suspect is a very flat unvignetted field. If the OAG doesn't rotate it's actually better for guiding as it stays square to the RA/DEC directions for mount corrections.

[Muzfox]

Ahh yes that makes sense, thank you.

I've got the scope now and she is a beauty, now begins the setup process. I do have to say EAF install was blindingly easy.

[ChrisV]

Might be a stoopid question. But will an oag provide 'noticebly' better guiding at 700mm focal length?

Just curious.

[Muzfox]

Honestly I don't think it's going to be a huge advantage, however it will be less wind load, less weight, 1 less dew heater to run etc so I can see advantages to it. I may even do a guiding comparison between the both to see if there are guiding benefits as well.

[gregbradley]

OAG leave guide scopes in the dust.

The problem with guide scopes is differential flexure. OAG don't suffer from that.

780mm is relatively short focal length but tracking errors will get exaggerated by the small CMOS pixels which are harsh on these sorts of error.

Will you get away with it? In a smallish final image it will be hard to notice but any close up look will show the non round stars in 5-10 minute exposures.

Greg.

[Sunfish]

Yep. I use an OAG on 800mm FL with 0.65 (f5.9) reducer and makes a vast difference with guiding . Better than 0.6 and I am not very careful with alignment routines.