ED100 Reducer backfocus question?

[tich]

Hi everyone I'm having trouble finding out where you measure the back focus on a Skywatcher ED100 0.85 reducer as some results are saying from the base of the threads on the rear where others are saying from the back of the glass, either way I've still got to buy yet more spacer adapters anyway as the one I have is to long but if anyone can help me with this issue then that would be appreciated thanks.

[x6gas]

It's usually from the base of the thread.  That's certainly the case for the flattener on my Esprit...

 

[tich]

Cheers for clearing that up hope you're well?

[Freff]

 

Hi Tich, on my Vixen 81s the specs say

Back Focus (from rear edge of focuser body)
Back Focus with Reducer (from rear edge of reducer) 

HTH

[tich]

Cheers Tony that clears up a lot of things now still means I've got to but more spacers though which is a pain...