Zwo OAG

[ergio1]

Hi everyone
Hope you are well.
I have an issue that perhaps you might be able to help with.

I am unable to get focus at the same time with the main camera and the oag cam.
My equipment is:
Qhy163m main camera
Evostar 72ED
Zwo 224 MC for guiding
Zwo off axis guider
Qhy filter wheel
Focus reducer (so have to be 55mm to the main cam sensor)

I think I have read online that I need to have the OAG as close as possible to the filter wheel - main cam.
Unfortunately the QHY filter wheel has a thread size of M54 so I must use a step down adapter to 48mm and this is about 6mm (space)

Please refer to attached image for details,

Much appreciated

[ergio1]

Sorry images here

[The_bluester]

Is it an M54 female thread on the filter wheel, and M48 female on the OAG, or is the OAG M42?

This adapter might help you and would reduce the backspace consumption to 2mm. But the threads might need to be turned shorter if they foul on the pick up prism on one side and the filters on the other. There is an M54 to M42 version as well.

https://www.siderealtrading.com.au/product/pegasus-astro-m54-male-to-m48-male-adapter/

[The_bluester]

Separate reply as I wanted to keep it apart.

Have you focused the main camera and then slowly moved the focuser in and out to see which direction you need to rack it to bring the guide camera to focus? That would be the best first step as it will tell you which direction the relative spacing needs to go to get the two cameras in focus together.

[ergio1]

Hi Paul,

This is great advice...
Just bought this adapter from sideral trading.

Also, you are correct. I was perhaps doing the wrong way. So I went and got focus with the guide cam first and later trying to get focus with the main camera. I’ll try how you have suggested.
Thanks

[The_bluester]

Well, either way will give you the info that you need, you just need to know if you have to rack the focuser in or out to focus the guider compared to the main camera to work out how the relative spacing needs to change.

Another one to be aware of, usually you can adjust the pick off prism in and out while the guide camera stays in the same place. So long as it is firstly not casting a shadow on the sensor and secondly it is well enough in the light path to get guide stars, if you adjust the prism outwards it effectively reduces the spacing to the guide camera and moving it inwards increases it. The vertical distance from the prism to the guider chip is part of the spacing.

[ergio1]

Thanks Paul.
I’ll complete this and hopefully it works now... fingers crossed 🤞

[Karlz]

Hi Ergio,

Best for OAG is to point at an distant object in the day and have your main camera focused on that then adjust the OAG camera to get focus. That's ow I did my ZWO OAG then it was a fine tweak at night.