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Re: [OM] Shooting paintings

Subject: Re: [OM] Shooting paintings
From: "C.H.Ling" <chling@xxxxxxxxxxxx>
Date: Sat, 30 Mar 2002 10:14:16 +0800
With the same lens, manufacturing will NOT create variation on distortion.
Distortion will be the same unless the design of the lens is change. I
guarantee anyone can see barrel distortion of your Zuiko 50mm non macro if
you have straight lines at the edge of frame. I have shoot a lot of testing
shots for my lenses from 16 to 300mm. No special testing chart, just the
building in front of my flat. Don't check the distorting inside the OM
viewfinder, it has barrel distortion itself.

C.H.Ling

----- Original Message -----
From: "John A. Lind" <jlind@xxxxxxxxxxxx>
>
> Based on several lens tests I've read on the "standards," I believe
whether
> there is *detectable* barrel or pincushion (using specific lab testing
> methods with test targets) varies from lens to lens.  IOW, manufacturing
> variations create some with slight barrel, some with slight pincushion and
> some with "none detectable."  Whether the "slight" detectable in a lab is
> "acceptable" in practical application matters much more versus what's
> detectable using a lab test target and highly specialized testing methods
> that are designed to specifically detect it and measure its severity.
>
> This should not imply the user "don't care about quality."  If it's not
> detectable in *practical* use, it's as if the aberration doesn't exist.
If
> you're seeking absolute perfection in actual lenses, you won't find it.  I
> guarantee every one of your lenses has barrel or pincushion distortion,
> including the 50mm Macros.  Non-debatable *fact*.  Building a lens with
> having absolutely, exactly, "zero" or "none" is like trying to balance a
> needle on its point.  It has not, cannot now, and never will
> happen.  Variation in manufacturing guarantees it.
>
> What might also be a fact is it's below detection threshold, even on an
> optical lab bench, which brings it back around to the need for it to be
> detectable in practical application.  Paintings with strong, exceptionally
> precise rectilinear lines are very, very rare.  I would look at the frame
> and its straight inside edges around the painting to see if there's
> anything detectable in the image by a human using eyesight alone without
> any aids.
>
> If this sounds strident, it admittedly is.  While it's worthwhile to ask
> questions about aberrations and distortions detectable in a lab, the most
> important question is whether the magnitude of it is detectable in
> practical use, making practical photographs.
>
> -- John



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