G'day Paul

While each of the above comments are quite valid, I note that you are an Adelaide 'tog
I would suggest that you arrange to meet with the other local 'togs to a) show them your system, and b) to maybe borrow a lens during an outing, so that you are in a better position to decide which way to go.

There are a fair lot of Adelaide AP members here, and I'm sure they'd love to spend some time helping you with this issue

If you like this idea, maybe a follow up msg here asking for that help would speed things up
Regards, Phil