Quote:
Originally Posted by Peter.M
So the aperture is only 160mm useable, this makes it a f3.75....
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Equivalent to, yes. I believe they call this a T-stop. So the F/ratio may still be F2.8 but the T-stop would be higher due to light loss.
http://www.youtube.com/watch?v=DzSlQRewS7Q
I discovered this with my f3.64 SN also being no real advantage over an unobstructed f5. It's a bit of a false economy really!