my tut on Poser camera starts at http://www.book.artbeeweb.nl/?p=3069 

on the 2nd page of it http://www.book.artbeeweb.nl/?p=3071 you'll find the full table of FoV's

you'll reach 90* at 11 mm focal length (measured as described in the webpages, so you can redo them if required)

My rule of thumb, which becomes more accurate at larger distances, is: when you step aside 1 mtr, and walk forward N meters, then you'll be at the edge of the image for a focal length of 12.5 * N mm. For FoV 90* this would result in 1 meter forward => 12.5 mm, but as said, the rule is not that accurate at shorter distances. 

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though