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[OM] Re: Aperture setting rules of thumb

Subject: [OM] Re: Aperture setting rules of thumb
From: AG Schnozz <agschnozz@xxxxxxxxx>
Date: Mon, 16 Jan 2006 15:25:04 -0800 (PST)
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.

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.

AG

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