Many thanks for that. I had no idea Lunt was responsible for the basic Coronado PST design.
The reason for my confusion was trying to square your mention of a tilting block on the sponge ring with my complete lack of one.
I had already guessed that only perpendicular compression was needed to tune my etalon.
Then discovered that my etalon was completely slack and
rattled freely over half of its
normal tuning range.
This was when the etalon was set on band by centring the original tuning hole in the housing cut-out.
None of this would be obvious unless the etalon was dismantled to allow it to be tuned with an external rod in the edge drilled, tuning disk.
Say I apply more pressure from the tuning disk, simply to maintain enough compression for mechanical,
location reasons.
Then it
should go off-band and remain out of reach until comprpession is re-applied by reversing in the opposite direction.
Which makes absolutely no sense at all. Perhaps there is another H-a band nearby if I apply far more pressure?
This seems highly unlikely and would make the tuning even stiffer at the other end of the tuning range.
Yesterday, we had freezing gales so I couldn't make any useful tuning trials on the sun to confirm or deny my findings.
