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    Kenko 1.4x and Canon 400mm f5.6

    Mention of a Sigma 500 f5.4 caught my eye and I decided to look into it. Well, it seems f4.5 was intended. It is an old design, and heavy for its max aperture compared to the Canon f/4 II. No interest to me. Now if Sigma would actually produce a new lightweight sharp 500mm f/5.4, that would be...
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