Julian Loke listed the Photodo performance figures for lenses with
comparable focal lengths to the EOS 100 - 440 IS lens.
However, has anyone seen performance figures, perhaps including MTF graphs,
for the Sigma 170 - 500? This lens is not mentioned on the Photodo site. I
get good pictures with this lens on it's own, but with a 2x converter
(Kenko) the results have been disappointing. For camera club competition
purposes, I make 12 x 16 inch enlargements in my darkroom and any
imperfections with regard to focus or contrast show up dramatically.
(Results on slide film are a little better, due to the inherently higher
contrast of the film.)
I also have Canon 2x and 1.4x extenders, which I use with my 70 - 200 f2.8.
All my results with this combination have been very good. I would also like
to get a 100 - 400 IS lens as a replacement to the Sigma 170 - 500 as it is
compatible with the Canon extenders. Has anyone had experience of this lens
with the above extenders? How does it perform? The combination of 100 -400
with 2x extender will give me 800mm, which is not too bad for wild life and
some bird photography. Obviously, with the 2x I will have to focus
manually, due to the f-stop going down to f11, but that is not a problem for
me. (I know that the 400 f2.8, 500 f4 or 600 f4 lenses with 2x extender are
first prize for this sort of photography, but I would have to mortgage my
mother-in-law in order to raise funds to buy one!)
Tony Mitchell
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