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Re: [OM] diffraction

Subject: Re: [OM] diffraction
From: "John A. Prosper" <prosper@xxxxxxxxxxxxxxxxx>
Date: Mon, 31 Jan 2000 18:46:58 -0500 (EST)
On Mon, 31 Jan 2000, *- DORIS FANG -* wrote:

|
|
|   So, what exactly causes diffraction? I'm not sure I understand
|the reason.

Just so there's no confusion, diffraction is NOT an aberration.  It is
a property of the wave nature of light.  As light rays shine through a
hole (e.g., a lens aperture), the rays tend to bend outward as they
pass through the edge of the orifice.  The smaller the hole, the
greater the tendency for the rays to bend.

The effects of diffraction are overwhelmed by that of lens aberrations
at wide apertures.  Conversely, at small apertures, diffraction
effects dominates whereas aberration factors dwindle to negligence.

For optimal lens sharpness, the ideal balance point is about three
stops down from max aperture where the cumulative effects of
diffraction and aberrations are at their minimum with respect to all
other aperture settings.



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