08-08-2011, 06:03 PM
[quote name='mst' timestamp='1312797599' post='10492']
I can only speculate why this doesn't work with the 150/2.8. Maybe it has to do with the effective aperture (with a 2x TC added, the lens is f/5.6 at large distances only).
[/quote]
That is my guess also. If you use a 1.4x on it, the focus range is limited to a shorter region than without, and the combination from memory is about 1:1 magnification at that point. I guess with a 2x they could have limited it further out again to maintain enough effective aperture, but for whatever reason they chose not to.
I can only speculate why this doesn't work with the 150/2.8. Maybe it has to do with the effective aperture (with a 2x TC added, the lens is f/5.6 at large distances only).
[/quote]
That is my guess also. If you use a 1.4x on it, the focus range is limited to a shorter region than without, and the combination from memory is about 1:1 magnification at that point. I guess with a 2x they could have limited it further out again to maintain enough effective aperture, but for whatever reason they chose not to.
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