WARNING: SOLAR OBSERVATION REQUIRES GREAT CARE AND SAFE FILTRATION.
INSTANT AND PERMANENT BLINDNESS CAN EASILY RESULT FROM SIMPLE MISTAKES. NEVER LOOK AT THE SUN THROUGH ANY LENS, MIRROR OR INSTRUMENT UNLESS IT HAS BEEN FULLY TESTED AND APPROVED FOR SUCH USE. YOU FOLLOW MY EXAMPLE ENTIRELY AT YOUR OWN PERIL!
My first trial on the sun yesterday required I swap the correct 80mm extender for a 40mm to reach focus. This introduced a 40mm error in the PST etalon position relative to the focus of the 6" objective. The rule is to match the PST's 20cm inside focus position for the leading edge of the etalon tuning ring.
My error was in using a 2" star diagonal which has far too long an optical path length.
There seemed to be no obvious way to connect the ITF/BF filter stack to a 1.25" star diagonal. Then I remembered I had a second, no-name 1.25" star diagonal.
Unscrewing the eyepiece holder provided a female thread which exactly matched the ITF's tubular holder. The 1.25" chromed spigot fitted a 2" to 1.25" adapter.
Using the 40mm extender after the AOK etalon adapters gave me the final piece of the puzzle. The 80mm extender can go back into the plywood ring in the tailpiece of the refractor to bring the etalon to the correct position.
I now have an awful cold so testing the new layout may be slightly delayed despite the usually rare sunshine.