Olympus-OM
[Top] [All Lists]

Re: [OM] Macro Lens

Subject: Re: [OM] Macro Lens
From: PCA Cala <PCACala@xxxxxxx>
Date: Mon, 23 Mar 1998 04:12:16 EST
Hi Foxy:

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

I used that lens many years ago.  It was kind of soft at the edges and
required stopping way down to get correction.  I seem to recall that at some
point I would loose center sharpness at the expense of increasing corner
sharpness.  (I put subject matter in the extremes of the view in my wide angle
shots, so it's noticable.  I also used some real high resolution films in
those days).

Actually, this lens behavior is typical of the lens test results in Modern
Photography.  They tested at all apertures and you typically see diffraction
caused degradation in performance at the smallest openings.  The 1/4 rule
looks about right: in 35 mm lenses this would start at f/8 for the center.  I
don't have any tests for wider lenses here with me at present.  But in wider
angle lenses you have more aberrations to contend with.  Stopping down
controls aberrations.  So one would not see diffraction caused performace loss
UNTIL the aberrations are controlled from stopping down.

This is an optical fact of life due to forcing the light rays through a small
diaphram.  But in practice there is increased depth of field which may make
the shots appear sharper at small apertures due to reduced circles of
confusion (yup, that is a real term).

Gary Reese
Las Vegas, NV

< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz