Thinking of swapping to OAG

[OK Apricot]

I'm thinking of swapping to an OAG setup instead of a guide scope. Obviously lighter but seemingly more difficult to get going initially? Is it a PITA to swap between scopes? Would like to use on both my Sharpstar and 80ED, and part of my thinking is to get used to OAG for when the time comes to get a C14 👀. What about rotation? I may have to rotate the OAG to get a suitable guide star but then that might throw off my framing when it rotates the main camera with it. What were your experiences going from a scope to OAG? Its either this or a small 30mm jobby I think. 

[Elp]

It depends on the OAG. With my main azgti setup I got guiding from 0.8-1.2 typical with a 50mm guidescope to around 0.5 at 360mm focal length with the oag, I wouldn't dismiss a change in seeing for the difference in the above.

You can set the OAG during the day, get the main camera in focus, then adjust the guidecam in the OAG.

I ultimately sold the zwo OAG I had due to having to setup and breakdown every time so setting it up was a pain.

I do now have another one for my C6 due to the focal length when shooting f6.3, the Celestron one has a rotating prism around a third of the diameter so you can reposition it. I believe some other brands also come with focusers which will make setting them up easier.

You'll need some sort of rotator with the SCT regardless as it doesn't have one built into the visual back I believe, it doesn't on my C6.

Edited January 30, 2023 by Elp

[OK Apricot]

I would say your improvement was down to the equipment but not nearly experienced enough to back it up with confidence! 

I feel like it would be simple enough finding common focus between the two cameras in daylight like you say, just the thought of potentially having to rotate everything to find a guide star puts me off. I have the 61EDPH II so the focuser and reducer have a rotator built in, but with a setup like this Reducer>OAG>Filter drawer>imaging camera I can't see how I'd rotate the OAG independent of the imaging camera. 

The C14 comment was a bit tongue in cheek - not in my lifetime 😂

[tomato]

I use a ZWO OAG on an Esprit 150 and to date (3 years of imaging) it has never failed to have a suitable star in the FOV so I have not needed to rotate it.

[Elp]

Yes but your mind will always be eyeing up another scope...

Usually there isn't much of an issue finding a guidestar, if the prism is a large one and you're using a mono guidecam that would be better.

[OK Apricot]

Ah OK, thanks chaps. The ZWO one is 8x8mm and the image circle from the Sharpstar reducer is 44mm. I image with the 533 so 11x11mm and guide with the 120MM mini - visualising it, I should be able to drop the prism fairly deep into the optical path without obstructing the imaging sensor, and I guess be more spoilt for choice for stars? 

It leaves me questioning the 80ED reducer - can't find much on image circle on that one, but again with the smallish sensor of the 533 in probably going to be alright, right? 

Edited January 30, 2023 by OK Apricot

[Clarkey]

I recently purchased the combined Antila OAG and filter drawer. A bit costly but has a large prism and makes changing the filter doddle. The one major negative of an OAG is having to recalibrate the guiding when re-framing targets. In theory you could set up the framing in advance, but I have found this challenging. As soon as you rotate the field, the calibration needs repeating. I have bounced between OAG and guide scopes for a while and I think I am starting prefer guide scopes where possible. Even at 1600mm using the RC8, the st80 works very well for guiding. I do have everything very secure to avoid flex. I think at long FL, such as an SCT, OAG is really the only option.

Fwiw, I see not real difference in guiding or star quality between the OAG and the guidescope. Seeing is way more influential on the results.

[Elp]

47 minutes ago, OK Apricot said:

I guess be more spoilt for choice for stars? 

You'll be surprised how many you'll pick up as you'll be using your main scope with a larger aperture. As your camera is mono it'll also help.

[Adam J]

3 hours ago, OK Apricot said:

I'm thinking of swapping to an OAG setup instead of a guide scope. Obviously lighter but seemingly more difficult to get going initially? Is it a PITA to swap between scopes? Would like to use on both my Sharpstar and 80ED, and part of my thinking is to get used to OAG for when the time comes to get a C14 👀. What about rotation? I may have to rotate the OAG to get a suitable guide star but then that might throw off my framing when it rotates the main camera with it. What were your experiences going from a scope to OAG? Its either this or a small 30mm jobby I think. 

Well, its more trouble that its worth for an 80ED but if your sure that you are going to eventually move to the C14 that makes sense.

What I would says is how do you currently polar align? If its with the guide scope then you are not going to be able to do that with the avaliable FOV on a off axis guider.

Adam

[OK Apricot]

7 hours ago, Adam J said:

Well, its more trouble that its worth for an 80ED but if your sure that you are going to eventually move to the C14 that makes sense.

What I would says is how do you currently polar align? If its with the guide scope then you are not going to be able to do that with the avaliable FOV on a off axis guider.

Adam

I'm assuming the trouble comes from the  focuser having to support the extra weight. 

I use the ASIAIR Plus so PA is done using the main camera. 

Also the C14 is but a dream. It would more realistically be an 8 or 925 😏

Edited January 31, 2023 by OK Apricot