I don't know. It may be a combination of considerations for image
quality. Wide open fast lenses designed without the parallel ray
considerations that Olympus finds so important may restrict one end of
the aperture range. At the other end with smaller apertures and the
small pixels used by Olympus you run into pixel diffraction much
sooner than the aperture diffraction that you see in Gary's tests.
While pixel diffraction would be present in any lens at moderately
small stops on an Olympus digital camera, Olympus may feel that
because an OM lens must be operated manually it requires a special
warning compared to lenses that can operate in programmed modes on the
camera.
Winsor
Long Beach, California, USA
On / November 11, 2007 CE, at 6:54 AM, Chuck Norcutt wrote:
> However, I've just convinced myself that it only has to do with
> metering. I haven't done all of them (only up through all the
> primes or
> zooms starting at 50mm or less) but Oly's recommended aperture ranges
> for the lenses I checked have a very poor correspondence with optimal
> performance as shown in Gary's lens tests. Optimal resolution and
> contrast on Gary's tests are very often achieved at apertures smaller
> than Oly's recommendations and, on rarer occasion, larger. There
> are a
> few which do correspond fairly well but, for the most part, no. For
> best optical performance I think you need to pay attention to Gary and
> ignore Oly's advice.
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