Do you intend to send guide signals to correct the mount's RA tracking. It's not needed for EAA and will complicate your setup.
The OAG's purpose is to provide a connection for a separate guide camera that picks off part of the light cone and sends it to the guide camera. Those images are processed by guiding software that sends signals to the RA tracking motor to speed it up or slow it down. This is what is referred to as "closed loop" tracking. It is common for long exposure astrophotography where you have to track an object to pixel level accuracy for 5 minute or longer exposures. Long exposures were driven by CCD technology that had very high read noise compared to today's CMOS cameras. For EAA, and Zwo cameras in particular, CMOS technology is used. It has much lower read noise. This enables stacking of many short sub exposures to build up an image that has a total integration time comparable to a single long exposure. Since sub exposures are measured in seconds or tens of seconds, guiding is not needed. The image doesn't shift in the frame enough to warrant guiding.
Get the T-adapter. It provides 50 mm of the 105 mm spacing for a 0.63 reducer. Once you have that, Zwo cameras come with spacers that provide the remaining 55 mm of backfocus. 55 mm backfocus comes from the T-mount system used by most DSLR cameras.
The final optical train will look like this: Scope's SCT threads > 0.63 reducer > T-adapter > Zwo spacers > Zwo camera
You can look on the Zwo website for how to use the spacers. There is a lot of material on how to get the remaining 55 mm of backfocus after you install the reducer and T-adapter.
Edited by dcweaver, 29 November 2021 - 12:41 AM.