Water Iris and Depth of Field

Down at the lake on a sunny bank holiday Monday with no plans as to what I was going to shoot I spotted these iris flowers that bees were busying themselves around.

Keeping the depth of field as shallow as possible to eliminate background distractions I used a Nikkor-S.C 50mm F1.4 at F4 for the 1st pic. The next 3 where taken with a Pentacon 135mm F2.8 (the Bokeh Monster) with a 20mm extension tube to reduce the working distance a little and also shot at F4. Camera again was the Canon 40D