Replying to myself, but I'm sure there will be others using 1600MMs and wishing to do the "slow upgrade" to 2 inch filters like I am, so I hope this post is useful.
This question is holding up a roughly $2k order to ZWO; I can't really proceed with the order unless I know this is going to work.
After reading various ZWO docs it does seem possible to have an imaging train with ASI1600MM + 2" EFW + M68 OAG with less than 55mm of back focus:
The 2" EFW has an M54 female connection on the camera side, while the ASI1600MM has an M42 male. So I need an M54 male to M42 female adapter to connect the EFW to the ASI1600. The EFW indeed comes with an M54 male to M42 female adapter, so that gets the camera connected to the EFW, and the adapter takes up zero backfocus. I hope ZWO staff will let me know if this is not possible for some reason. I will probably also need a 6mm M42 spacer in-between the 1600 and EFW to keep the OAG cam and imaging cam parfocal.
The M68 OAG bolts onto the 2" EFW.
I then bolt on the ZWO M54 tilt adapter (purchased separately) to the M68 OAG. The M54 tilt adapter has an M54 female connector on the scope side. My reducer has an M48 male connection, so I need an M54 male to M48 female adapter. The 2" EFW comes with this adapter, and it takes up zero back focus. That completes the imaging train.
My calcs suggest the total back focus without the 6mm M42 spacer is 49mm, so well within the 55mm backfocus spec of the reducer.
So, what do you think ZWO? Can you confirm that this is possible, and at the same time have the guide cam and imaging cam par-focal? Is there something I am not considering?
Thank you,
Ross
