Connection for proper backfocus for 6200mono EFW to a GT71 with a Flat 6AIII

Hockensmith

I have finally received the ZWO6200mm w/filterwheel kit to use with a William Optic GT71, and I have a general question regarding the assembly sequence that will achieve the proper back-focus.

The telescope camera chain is as follows: William Optics GT71 with a Flat6Aiii ( I need an appropriate combination of spacers) to connect to the ZWO EFW filter-wheel and ZWO6200mono. What are the correct rings to create proper back-focus. (This setup will be using a separate guide scope/camera and ASIAIR.)

Here is a Dilemma: The Willam Optic Flat6AIII info states that back-focus is 64.1, whereas the info with the ZWO6200mono states that the back-focus is 55mm. Who's information is correct? (and, if your ring combination is millimeter off ... how big a problem is that?)

Can anyone shed light clarifying the conflicting info and how to assemble the proper ring combination to accommodate this telescope to camera chain? ~ John Stephen Hockensmith

wvreeven

A camera doesn’t require back focus but a flattener does so 64.1 is connect. Attach the EFW to the camera and then just add spacers to get the correct back focus distance. With the 16.5 and 21 mm spacers included with the camera you’ll reach 55 mm so add 9.4 mm worth of rings and spacers to get to 64.1 mm.

Hockensmith

Is the best way to achieve 9.4 to use the Stellavue 8-12 variable tube