Usually, a wider-aperture version of a lens will have the same number or
more elements than a smaller-aperture version, assuming other things are
equal (focal length, type of glass used, quality of final image, ...).
Zuikos follow this rule, EXCEPT for the 200mm. The f4 is 5 elements in 4
groups, while the f5 is 6 elements in 5 groups.
Having an extra element and an extra group means that there are more
surfaces from which light can be scattered, resulting in principle in a
lower-contrast image (but the difference might be so slight as to be
undetectable in real use). However, the extra element gives the lens
designer an extra degree of freedom to further reduce abberations, and so
improve the quality of the final image. So the f5 might actually produce
better-quality images than the f4. Of course, the lens designer might have
chosen to use the extra degree of freedom to reduce the length of the lens,
whilst maintaining the same image quality as the f4. As we are not privy to
the lens-designer's intentions, we cannot really predict which lens will be
better -- one needs to test the lenses side by side to see which is better.
I have never seen any tests of the f5, but the February 1981 edition of the
UK photo magazine "Practical Photography" reviewed the f4 in a group test of
6 Zuiko lenses. At that time, Practical Photography did MTF tests of
lenses. This is an extract of what they had to say about the 200mm f4:
"This particular OM tele isn't a high flier in optical terms. Central
definition, though consistent, peaks at a relatively modest figure by f11.
Other apertures are capable of giving perfectly decent images, but the
centre doesn't soar like other Zuikos. Nor is edge definition anything to
shout about. From full aperture up to f16, an adequate performance is
demonstrated, but f22 and f32 look decidedly dodgy if well-resolved detail
is what you seek at the edges."
In the conclusion to the reviews, they said:
"The 200mm is the greatest disappointment. Though this telephoto is
compact, fast enough at f4, and handles well, its optical performance
(particularly at the edges) never climbs above adequate."
The MTF results were shown as bar charts. I have read off the values as
best I can, and show them below, along with the values for the 50mm f1.8
(the values for the edge are shown in parenthesis):
200mm f4 tele: f4=46(41); f5.6=48(40); f8=49(40); f11=55(41);
f16=52(48); f22=41(32); f32=28(25);
50mm f1.8 std: f1.8=54(46); f2.8=57(52); f4=82(69); f5.6=85(75);
f8=84(77); f11=72(71); f16=51(52)
I have got the 200mm f5. I bought it rather than the f4 in order to
minimise weight and size, and maintain a single filter size (49mm). I have
not used it much (yet) due to the slightly awkward focussing. Being f5, the
microprisms on the standard focussing screen are virtually useless, and the
split image works ONLY if your eye is very near to the optical axis --
displace your eye only slightly and one segment of the split image darkens.
>From Cy in the UK
----- Original Message -----
From: <voop@xxxxxxxxx>
To: "Zuikoholics Anonymous" <olympus@xxxxxxxxxxxxxxx>
Sent: Thursday, June 06, 2002 10:43 PM
Subject: [OM] Zuiko 200/5 ?
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