[wim]

The SA feature affects the whole image frame. The portion that is in focus remains more or less intact but there is a loss in image quality there as well.

I found that a weird option as well, at first. I guess they wanted somehow to create a lens to replace the 135 SF of yore, and probably thought it a good idea to include it with the macro. The 100 mm FL is more of a portrait FL than 135 mm is, and F/2.8 is more or less the maximum aperture you can use for a reasonable DoF for tight headshots with a 100 mm, especially with soft focus. Offering it as a separate lens would probably not have been practical from a manufacturing, sales and marketing POV. So I do understand why they chose to add it to this particular lens.

Having said that, I have seen quite a few macros taken with this lens, and IMO it renders way better than any of the older 100 mm macro lenses IMO. Despite being an IF lens, I am actually considering it as an addition to my kit because of that rendering.