I read somewhere that if one designed a very good lens with no
aberrations it would be most sharp when wide open and that a
softening would be seen with each stop down as the diffracted light
at the aperture is added to a decreasing total amount of light
passing through it. What we have in practice is the limitations of
lens design being mitigated a bit by stopping down, but then being
overtaken by diffraction. So your Leica lens example is probably a
statement about the high quality of the lens correction to begin with.
Winsor
Long Beach, California, USA
On Jun 7, 2005, at 2:43 PM, om2@xxxxxxxxxxxxxxxx wrote:
> In fact, many high performance designs start to degrade even at f/
> 8, which
> is usually the sweet spot for most lenses. I speak particularly of
> Leica
> lenses, which are usually best between f/4 and f/8.
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