It would be interesting to try the 9-18 behind the 3,5 dome. I would be happy it it was possible to optimize fore the wide end and just use that, skipping zoom. Providing that part of the soft corners are caused by lens nodal point being off the dome's optical center.
As i mentioned: i've been suggested 2 20mm extensions + the 4.33" dome should work with the 9-18. That would be interesting to get a second opinion on.
A measurement of the nodal point shift of the 9-18 (and other lenses) can be found here:
The nodal variation is 6mm between the ends of the zoom, is that excessive?
Edited by oskar, 05 February 2014 - 12:59 AM.