Canon 400mm lens mounted

[Bottletopburly]

Killed an hour fettling in the shed using some acrylic plastic as a losmondy plate and using a spare guide scope ring for stability now my canon 400mm zoom lens is mounted thigh I need another 10mm spacing to give 55mm back space  but small thing to sort but this will give me a fov to capture M31 without being too crammed in using either the 585 sensor or the 533 sensor with a fl of 200-250mm , all that’s left is to mount guidescope bracket on to take my qhy mini guide scope and some clear nights , not sure how stable the focus will be but I acquired a bahtinov mask recently and I read this lens works about right stopped down  to 3.8 , if anyone knows different then let me know.