I wonder if this might not be due, at least in part, to a very slight
difference in focal plane and depth of field. The lower right corner is
closer than the other corners where one can distinguish fine, high
contrast detail. The lower left corner is subtle and not very contrasty
foliage and the upper corners are further away. I know an 18mm lens has
great depth of field, but it is not infinite and the COC for these full
pixel images has to be pretty small. F5.6 is only 1 & 1/3 stops down
from wide open. Also, of course, focusing a fairly slow 18mm lens
accurately in a small viewfinder isn't that easy. Really too bad the
Varimagni doesn't fit.
I note what Gary said in one of his 18/3.5 tests: "lens design
emphasizes outer zones at expense of center image zone (which gives a
sharper overall impression of an image); overall optimum aperture at
f/11." If it were my equipment, I'd be tempted to try f8 and f11 too,
even though f11 is outside of Oly's recommendations.
Moose
chling@xxxxxxxxxxxxx wrote:
>Yes, you are right about the lower right corner performance but on other
>corners and center the zoom are slightly better.
>
>C.H.Ling
>
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