Acer,
Looks like a slight amount of "pincushion" distortion; straight tangential
lines near the edges bowing inward toward the center. If they bow outward,
it's "barrel" distortion.
The theoretical rectilinear lens won't do either. In reality, most
rectilinear lenses have a very slight amount of one or the other, and it
can vary from sample to sample of the same lens. It's caused by the lens
having less axial magnification than off-axis. Barrel is the opposite,
with greater axial magnification than off-axis.
It's least desirable in a shift lens that would likely be used for
architectural work with many straight lines being commonplace. In other
types of images without straight tangential lines in them it's not very
detectable.
-- John
At 20:48 1/14/01, Acer asked:
i was looking at some old pix, and came across this one with the
28/3.5. note lower step, it seems to be concave down (sorry no idea what
to call it) while the upper step is level all the way across. is this WA
distortion at the edge? what is is called? thanks,
http://albums.photopoint.com/j/View?u=380427&a=9125406&p=31108137&Sequence=0&res=high
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