Back focus baffling me

[stevenson166]

Hi all, I am struggling with Back focus...i think i need to get as close to 55mm as i can , so i have read. I am trying to connect a ZWOASI120MS-C  (Back Focus 12.5mm) to my small refractory scope Astair Astro 66m ED-R , i have purchased a 0.6x Lightwave reducer but need to make up the difference.... any ideas greatly appreciated.

[geordie85]

https://www.firstlightoptics.com/adapters/baader-varilock-46-lockable-t-2-extension-tube.html

[stevenson166]

Wow, Is it as simple as adjusting this to 42.5mm ?

[geordie85]

Yep