As I review the test results on Gary Reese's site I note that many, if not
most, wide angles and short zooms demonstrated measurable distortion -
usually barrel, sometimes waveform.
Here's the question: short of repeating Gary's tests, can such distortion be
reliably detected through the viewfinder? If so, this would certainly
simplify shopping.
However I suspect this would not be a reliable method. For example, certain
of my Canon lenses appear to show significant distortion through the
viewfinder: at close range the 50/1.4 seems to show gross barrel distortion;
the 100-300/5.6, pincushion distortion throughout the focusing range. Yet
photographs show little or none of this - certainly nothing approaching what
I see through the viewfinder.
Also, in reading Gary's tests, I wonder whether it is even possible to make
generalized statements about the performance of certain lenses, particularly
zooms. For example, even the extraordinarily expensive 35-80/2.8 Zuiko
tested demonstrated barrel distortion at 35mm. The several other 35-70mm
zooms (f/3.5-4.5, f/3.6 and f/4) varied considerably in distortion,
resolution and contrast, even when different samples of the same model were
tested.
Granted, most of us have differing standards and even sensitivity to optical
characteristics. Gary mentioned finding disturbing distortion in a photo of
cactus, taken with the 35-70/3.5-4.5 Zuiko, while Tom and others have
expressed satisfaction with the same lens. I've seen many online images
taken with those lenses and see nothing objectionable - given the
limitations of online viewing.
Finally, I'd certainly like to see any examples of these types of
distortions that are clearly visible in photos our listfolk may have;
something along the lines of the excellent examples David I. Vila and CH
Ling recently provided regarding chromatic aberrations in the Zuiko 180/2.8.
(Much as I'd like to reciprocate, the best I can offer are now-familiar
examples of extreme curvature produced by my semi-fisheye adaptor in photos
of Fort Worth's Flatiron Building - unless you'd like to see even more
distorted pix of my grandkids taken with the same lens just for fun.)
===
BTW, a couple of years ago I decided to test assertions that makeshift
close-up optics cannot produce satisfactory flat field photos. Using the
Vivitar 2x macrofocusing teleconverter in combination with 50mm, 35mm and
28mm lenses. In each case both the lens and teleconverter were focused as
closely as possible (some compromise was necessary with the 28mm, since the
filter ring would practically have touched the subject!) to reveal any
close-focusing error.
To my eyes the photos were uniformly sharp and free of distortion at the
center and edges. The problem? My subject was a crisp new Andrew Jackson.
While the film was b&w (T400CN, actually) and only a fraction of the bill
was photographed, I'm reluctant to publish my results online - for obvious
reasons.
-----------
Lex Jenkins
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2b XOR -2b ... that's the equation - Ur Amblet, 'The Very Bad Quarto'
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