[Stephen65]

You should check William Optics webpage, it will clearly state that the FLT110 is FPL53 glass

That is incorrect, both because the WO webpage does not state what glass the FLT110 uses and because it uses FPL51.

The FLT110 and ZS110 use exactly the same TMB designed triplet airspaced lens, they just have different tubes and focusers. Both use FPL51, as confirmed by WO in this CN discussion about 3/4 of the way down the page:

http://www.cloudynights.com/ubbthrea...fpart/all/vc/1

As for the focuser on the ZS110, as you've noticed already Narayan there is much discussion on the WO yahoogroup about its pros and cons.