Sorry, but this is simply not correct.
With point sources an 11 inch F10 scope is identical to a F1.8
Only aperture counts with point sources (eg stars).
You might also want to have a look at Greg Bradley's recent effort....
http://upload.pbase.com/gregbradley/...06659/original
[quote=gerry aarts;295898]
(8 minutes at f1.8 is the equivalent of around 120 minutes at f10)
/quote]