Quote Originally Posted by Lee L View Post
The duplex method is shown in the book as a correct method with a flat sensor incident meter (or perhaps an invercone), not with a domed meter.
Yes. I re-read mine recently and realised it was for a flat receptor and that the dome style diffusers automatically carry out the duplex calculation.

If I get a bit of spare time tomorrow I might do some experiments with my Weston meter with its invercone and a Zeiss Ikophot with it's flat diffuser to see what the variance is as I thought the invercone behaved as a dome rather than a flat receptor as you suggest. I suppose I should go and read that chapter again!.