Begin forwarded message:
Date: Mon, 24 Feb 2003 23:18:16 -0800
From: Gary Reese <pcacala@xxxxxxxxxxxxx>
To: Olympus Digest <olympus-digest@xxxxxxxxxxxxxxx>
Subject: Re: [OM] Looking for 50mm f2 Macro info!
The most informative lens test I have ever seen on the 50mm f/2 Zuiko
Macro
was Norman Goldberg's Popular Photography's (PP) split image contrast
test.
For some reason it was left off the compilation of PP lens tests on
Lee
Hawkins site at:
<<
http://brashear.phys.appstate.edu/lhawkins/photo/pop-photo-zuiko-tests.txt
>>
perhaps because an interlibrary loan took too long to get me the
photocopy
and I took too long to get the data to Lee. So here are the charts
converted
to data points:
50/2.0 MC (Popular Photography 4/86, p. 106 (w/OM-3 test, pp. 30-3),
serial
number 101356):
Performance at infinity:
Actual focal length & T-stop: 52mm f/2.08
Distortion: none
Centering: near perfect
Vignetting: none beyond f/4.5
Flare: 0.44%
Transmission: 95.4% (T-stop f/2.18)
Percent contrast of 0.01mm slit image:
2 2.8 4 5.6 8
Center 69 73 80 84 83
1/3rd out 58 60 79 84 84
2/3rds out 50 58 65 70 75
Far edge 51 55 68 76 80
Performance at "macro" limit:
Actual focal length & T-stop: 40mm f/3.12
Distortion: none
Centering: near perfect
Vignetting: none beyond f/4.5
Flare: 0.44%
Transmission: 95.4% (T-stop f/3.27)
Percent contrast of 0.01mm slit image:
2 2.8 4 5.6 8
Center 60 68 69 70 77
1/3rd out 47 54 60 69 71
2/3rds out 38 40 50 55 65
Far edge 30 31 40 45 55
Noteworthy are:
* f/8 is the optimum aperture
* performance degrades at close focus limit, perhaps showing the near
AND far
aberration correction (floating elements) mechanism actually favors
near
macro distances (but what distance???)
* focal length is decreased at close focusing distances, which
indicates
there is some internal focusing going on and probably a reduced
barrel
extension at 1:2 over what would occur in a lens without floating
elements
and/or internal focusing.
So how does infinity performance with the 50mm f/2 compare to a fast
prime?
Unfortunately, there is only the 50mm f/1.8 F.Zuiko (serial number
1245831)
to compare slit image contrast data to. Presumably it is also
measured at
infinity. Again, this lens report never made it to Hawkins site:
50/1.8 SC (issue date unknown, p. 115):
Actual focal length & T-stop: 52mm f/1.89
Distortion: slight barrel
Centering: perfect
Vignetting: none beyond f/3.5
Flare: 0.86%
Transmission: 96.9% (T-stop f/1.95)
Percent contrast of 0.01mm slit image:
1.8 2.8 4 5.6 8
Center 60 75 84 85 84
1/3rd out 50 69 80 86 85
2/3rds out 35 45 52 68 76
Far edge 50 56 70 70 75
This would have been a black snouted "SC" lens, produced in the late
1970s.
The optical design of this lens favored the far edge at the expense
of the
2/3rds out zone. The strip down report on this lens is revealing. It
reports
the "actuating arm [to the auto diaphragm mechanism is] cushioned
with
resilient plastic bumpers against noise and vibration." So, yes,
Olympus was
aware of auto diaphragm induced vibration!
This slit image contrast data was relativized to all lenses ever
tested by
Popular Photography in my posting:
<< http://zuiko.sls.bc.ca/swright/archives/1998/msg02665.html >>
where I specifically and favorably compared it to a Leitz Summicron-R
50mm
f/2.0. It is interesting for me to revisit it because that analysis
lead to
me doing my own testing, resulting in the Zuiko Lens Test web site
and its
getting cited in Darkroom Techniques. That eventually culminated in
a LUG
member blowing off my results because they were based on a not widely
used
film. I still get a chuckle out of that one, especially because the
same
individual never produced any data of his own!
So, Albert. You often ask about available lens test data. But doesn't
what we
already know and have already posted to the web leave us with many
more
questions about what we don't know? The easy part is posting links
or even
mirroring data available elsewhere, but what we need is new data.
Like what
is the performance across the board of Zuikos at 1:10, or infinity?
Or the
macros at, say 1:2.5 ? FWIW, I did make the claim in 1998 in the
above cited
posting:
" . . . the OM-4Ti or OM-3Ti with a 50mm f/2.0 macro is "Leica-land."
"
Gary Reese
Las Vegas, NV
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