- Aug 16, 2012
aceflibble said:Internally-focusing macros have to use strong focus breathing to focus down to 1:1 (let alone beyond), and it takes a bigger toll on transmission, too. For example, the Canon 100mm f/2.8L IS Macro, when it's at absolute 1:1, is actually about 72mm t/7.4. (Give-or-take for minor copy variation and specific shooting scenario; I haven't used the EF-S 60mm or non-L 100mm to have their measurements to hand.) Of course weight and cost also go up.
Externally-focusing macro lenses can go to whatever magnification you want without changing the actual focal length, and though of course light is lost as the lens extends, it's usually not actually as much of a loss as when the lens has to shift everything around internally. That's the benefit to simpler designs like this. So this Sigma probably stays at 70mm no matter what magnification you want, and likely gets no darker than t/5 or so.
Ask, and the forum educates. Thank you for a super helpful post -- very much appreciated!