14" Double Truss build - setting back focus...

[coatesg]

I have been busy of late, trying to finish off my rebuild of a 14" newt - and we're almost there! (I do a fuller post when it's up and running).

I am at the point of trying to set the back focus (the tubes are fairly close to length, but they will need a little trim...).

This is going to be used for mostly imaging - what are people's preferred back focus distances? Currently, I have about 32mm from the fully racked in position to the focal plane (worked out by very stopped down solar projection). I'll be using an MPCC, so I'll need 55mm I think - does increasing the backfocus to about 65mm sound about right here? 

Clearly don't want to vignette too much, but still need to reach focus...!

Cheers

[saac]

That's a fantastic looking telescope Graeme. Sorry I can't offer any advice on the back focus but I was just about to ask similar so I'll be reading with interest on any advice offered. Good luck with the remaining part of the rebuild.

Jim

[coatesg]

Thanks  I'm quite pleased with it, but a bit of work needed yet...!

I'm probably going to shoot for 65mm back focus unless there's any other responses - a standard T-ring needs 55mm from focuser top to plane, so that gives me 10mm in-focus. While the MPCC may push it out a little, that's well within range of the focuser (a 1.5" low position comp ring drawtube in the Moonlite).