> AG Schnozz <agschnozz@xxxxxxxxx> wrote:
>
> Wayne asked:
> > I'm not sure what you mean by "symmetry" in this context -
> > please explain.
>
> Seeing that it's been months since I wrote that I'm not exactly
> sure which trait I was referring to. However, here is one
> possible explanation:
>
> Prime lenses generally fall under two or three major "lens
> formulas". Some lenses are what we would call "symmetrical".
> Look at a lens with the caps off through the front and the back.
> If the "hole" appears the same size through either end, it's
> symmetrical. In a world where all else is equal, this
> translates to objects equal distant from the focus point being
> rendered in the same OOF manner. With most modern zoom lenses,
> the OOF characteristics of close objects render differently than
> far objects in reference to the focus point. Retrofocus designs
> are not symmetrical.
>
> Zuiko Lenses that are very close to symmetrical, and render
> predictable OOF characteristics both front and behind the focus
> point would include the 35/2.8, 40/2, and "some" of the 50mm
> lenses. The 50/1.4 comes to mind.
>
> The 135/3.5 and 50/3.5 are two lenses that comes to mind which
> are anything but symmetrical.
Thanks for the detailed explanation Ken. I presume the "telecentric" lenses
for the 4/3 format will be much more asymmetric than those for OM.
>
> Another aspect, which I'm still getting my braincells around is
> the apparant increase in perspective distortion with the 4/3 and
> 2/3 sensors. I seem to have to correct perspective more with
> the digital cameras than I ever did with film.
>
Perhaps this is due to the handling of the camera, in the same way that you
mentioned having to level your horizons maybe you're tilting the body more in
all 3 dimensions than you would with an OM.
...Wayne
Wayne Harridge
http://lrh.structuregraphs.com
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