Here is a nice bit on Defraction

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

And here

http://www.dgrin.com/showthread.php?t=58028

All most missed this..Hard to take that TC off but for shots like this, ya, ya easy to plan for, you can get more DOF at f8 if you do. I would not go past f11 with the combo, you want detail with the DF and that lens goes into defraction at a fairly low f stop. OR you can be back a bit more= increase DOF and crop, that combo works well with hefty crops.

I love the damselfly and I think Sean is right that the shell is it's cast off nymph casing. That's totally cool.The DOF is a bit shallow here, and I'd like the damselfly a little brighter, but understand you were flirting with blown highlights in the lily flower.

Agreed about the DOF, but it's a cool shot nonetheless. And yeah, at 420 mm, you'd have to close down that aperture even further to the neighborhood of 24 or 32, depending upon the lens' capabilities

I wonder if the shell of the nymph is from the dragon fly we see here

interesting shot. I'm thinking more DOF might be better in this case,
what surprises me is even at F8 it is very shallow, must be because it's at 420mm