Trilling a double sharp in Beethoven's 3rd Moonlight

[tunneller]

Hi, on bar 32 of the 3rd movement of Beethoven's Moonlight, there is an octave of F double-sharp with a trill on it. I figure thumb and 4th finger to do the octave and 5th finger for the trill note.... er... what note is that? G sharp? [That'll be tricky with 4<->5?]. Should I start on the F or the G? My version actually has some confusing finger notation just a "4" (not a "54" or "44").

And then in same bar there is an ornament E-sharp, F, to Gsharp octave. What are the rules for that F - eg is it still a double sharp?

Thanks, T.

[pianowhisper]

Hello,

The upper note of the trill should be a G#. It's been a while since I last played this sonata but I'm positive I played the F## octave with 1-4 fingering, as it is indeed written on scores (or most of them, I believe).

For the trill, I'd say you should release your thumb from the bottom F## while doing a gentle rotation of your wrist + slightly moving your forearm to the right. This should allow you to reach the G# with your 5th finger in a movement that feels very natural. If your hands are big enough you can try to play the F## octave with 1-3 and then perform the rest of the passage resulting in the G# octave with 1-4.
I might be wrong but I believe that, for Beethoven, trills were usually, if not always meant to be played with the main note first, so in these octave-trills passages you should definitely play the octave first and then perform the trill/turn.
As for the ornament you mention (which constitutes the "turn" I just stated), the F is still F##, just like the A is still A# for bar 30.

Hope this helps!