[stephen2615 (Stephen)]

Greetings,

I have a William Optics (WO) Z61 with a WO Flat 61A field flattener and a (38 mm thick) 48 mm T mount adaptor for my Sony camera. In a moment of Black Friday madness I purchased a ZWO Off Axis Guider which is 16.5 mm thick. The documentation on the WO site is primarily for Canon or Nikon cameras and it doesn't mention the Sony cameras. The Flat 61A says it has to be set at 12.9 mm (purportedly camera non specific). After some measuring, that 12.9 mm is not for a Sony camera like mine. It should be 11.7 mm. Back focus for the Flat 61A HAS to be 55 mm. This means that given the T mount is 38 mm, the OAG is 16.6 mm, I understand that the distance to set on the Flat 61A is 0.5 mm to give that 55 mm back focus. I haven't tested it yet due to the never ending wind recently but does that sound ok? This does limit my options to put in a Clear Sky Filter as there is no room for it in the 55 mm limit. A clip in for my camera seems the only option. You could buy a thinner T mount for the Sony but it has disappeared. Does anyone have one and are my calculations about back focus correct when using my equipment. Thanks for taking the time to read this.

Stephen