Tom Reynolds wrote:
The 90mm is a closeup super macro lens. I would not use it for these semi-macro shots. I would rather but a 2:1 TC on the 100-400 if I needed more magnification. I like the working distance for these semi-macro shots and I don't see better images from the 90mm.
That being said the 90mm @ f/11 at about a foot produces very nice macro shots, probably better than the 100-400 but you won't see it on the web.
To add to this, if semi-macro is taken to mean about 0.25 (full-frame 0.5) magnification, then the 90mm lens has this magnification at 0.5 m. This is arguably a bit too close. Not impossible, for sure, but I would prefer keeping a distance of 1 - 1.5m for semi-macro (e.g. for butterflies on flowers).
Some other lenses are indeed better suited for semi-macro, like the 100-400 at 400 mm that has a 0.29x magnification at 1.3 m min focusing distance. I like the 300 mm F4 with the magnification of 0.24x at 1.4 m because of the up to 6 EV steps 5-axis Sync IS and the exceptional IQ of this lens that seems to accept teleconverters nicely, without loosing much of the IQ.
These are two quite distinct situations: when one can get really close to a subject for true macro (when the 90mm lens would shine), and when one must shoot from a distance of 1-1.5m (or even longer sometimes) for different reasons, for example, because there is a body of water or other impossible terrain between the subject and the photographer.