Thanks for the tip ChuckP, I'll have to bear that in mind.

Interesting what you say about it being approx 28mm in 135 terms, I'd always thought the 90mm was equated to around a 28mm, which is why I've always had trouble getting in spired with it. Slightly wider (21mm) or longer (35mm) and I just seem to be able to find the right angles much easier. Either way, I think this particular 90mm of mine will be going anyway, it's just ridiculously big when you're stuffing it all into a very conservatively sized backpack!