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Re: [OM] Various lens sharpness numbers at various apertures

Subject: Re: [OM] Various lens sharpness numbers at various apertures
From: "Terry and Tracey" <foxcroft@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 9 Jan 1999 16:33:33 +1100
I posted once that I heard you should not use an f stop smaller than your
focal length/4. This seems to work. Gary (one of them) says the 50mm f3.5
looses sharpness at f22 for example.

Then this got posted as a reply and hits it right on the head.

Foxy

Wrote Foxy:

>Does this mean I'm getting difraction when shooting with my 28mm f3.5 at
>smaller than f8? I haven't noticed any.

You are always getting diffraction! It occurs whenever the light waves pass
an edge, such as the edge of a diaphragm blade, or for that matter that of
the
mount when the lens is wide open. When stopping down, proportionally more
of the light waves have to pass the d... edge, so that diffraction
increases, and
at last it becomes the major cause of unsharpness.

However, only a really good lens can be 'diffraction limited' at small
stops.
Normally, lens aberrations are more prominent, especially wide open! But
without them, diffraction would actually mean that fast lenses would be
sharper than slow lenses, period. Warum einfach wenn es kann so schön
kompliziert sein?


Vänliga hälsningar/Best regards
Lars Bergquist
-----Original Message-----
From: Dave Bulger <dbulger@xxxxxxxxxxxxx>
To: OM List (E-mail) <olympus@xxxxxxxxxxxxxxx>
Date: Saturday, 9 January 1999 1:27:am
Subject: [OM] Various lens sharpness numbers at various apertures


>OM Gurus,
>
>After about 25 years of avid shooting, I'm just now getting into the more
technical aspects of this hobby/obsession/trade (i.e. I've just learned the
zone system) and I'm seeing more & more references to the fact that a lens
is not necessarily at it's sharpest stopped down to it's minimum aperture.
This is gonna bug me until I know exactly what aperture each of my lenses is
sharpest at.
>
>I've checked the FAQ and various other sources on the net to no avail.
Anyone have a source for this info?  I have a nasty feeling someone is gonna
refer me to the unattainable OM-System Lens Handbook...
>
>TIA!
>
>Dave




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