08-08-2011, 07:41 PM
[quote name='mst' timestamp='1312831276' post='10523']
You can of course focus closer manually. At MFD, the combination has an effective aperture of f/8 wide open (and for the record: f/11 with the 2x TC).
[/quote]
I noticed that when I was buying the non-OS version of the lens. Sigma's own web pages also state no AF with 2x on it, although not why.
Maybe my calculations are a little out, but I make it effective f/9.6 and f/16.8 with the 1.4x and 2x both at MFD. That's based on (1+magnification)*aperture so:
(1+1.4)*2.8*1.4=9.6
(1+2)*2.8*2=16.8
Or am I applying that incorrectly, or fails to take consideration of some other effect?
You can of course focus closer manually. At MFD, the combination has an effective aperture of f/8 wide open (and for the record: f/11 with the 2x TC).
[/quote]
I noticed that when I was buying the non-OS version of the lens. Sigma's own web pages also state no AF with 2x on it, although not why.
Maybe my calculations are a little out, but I make it effective f/9.6 and f/16.8 with the 1.4x and 2x both at MFD. That's based on (1+magnification)*aperture so:
(1+1.4)*2.8*1.4=9.6
(1+2)*2.8*2=16.8
Or am I applying that incorrectly, or fails to take consideration of some other effect?
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