Many thanks! I spotted on another forum that folks have been using the Tokina 10-17 with the D800 set on the DX crop. I hadn't thought of that. Doh. And I've got a TC 1.4 too.... so some things to try out first.
..... thanks for the Sigma 15mm tip. I'll take a look at that.
But a DP-FE2 won't fit directly on a Type 3 mount on the ND800? Will it fit with a 20mm (or less) extension ring? How about a Type 4 mount and the adaptor to fit Type 3 ports?
... and then problems with focussing rings. Man, nothing is ever simple eh?!?!
I thought one advantage of a switch to the ND800 would be using fibre optic links to Inon Z240s and then the ability to TTL (for macro). But I'm just waiting for someone to say "ahh, yes, it's not that simple......."