Whilst perusing old Oly reference material today I was reviewing the R.
Lee Hawkins/Michael Covington page at
<http://brashear.phys.appstate.edu/lhawkins/photo/olympus.faq.html> and
rediscovered the test data on OM lenses from Modern Photography.
Since there was recent reference on the list to "S" series "consumer
grade" lenses I decided to look up the Zuiko 35-70 3.5-4.5 which is an
"S" series lens and also one of my favorites. I was more than a bit
surprised to see that this humble piece of glass garnered "excellent"
under all test conditions and less than 1% distortion at the extreme
ends of its range. No wonder it's one of my favorites.
But then I also decided to look at the actual resolution values and see
that, though "excellent", they really only range from 56-63 lines/mm.
Interestingly, the best center resolution in the Modern tests was an
early (4/73) 50/1.8 at 90 lines/mm. The best corner resolution was 62
lines/mm achieved by several late 80's design lenses.
This brought me back to my E-300/C*n*on 20D question of last week where
I asked whether the OM lenses really have the resolution required to
make full use of an 8MP sensor.
The E-1 has 147 pixels/mm, the E-300 has 188 pixels/mm and the 20D has
156 pixels/mm. Seems to be a long stretch from even 90 lines/mm. Or is
it? I am always confused about lines per mm and line pairs per mm. Are
they really different terms or do they really mean the same thing. And
how do I relate pixels/mm to resolution as we used to in film. Does the
E-300's 188 pixels/mm translate into 94 line pairs/mm? Do I only need a
lens of 78 lines/mm resolving power to make full use of the 156 lines/mm
on the E-1 sensor? Or is this all more complicated by having to use a
"system resolution" formula as we did in film?
(1/Rs)^2 = (1/Rf)^2 + (1/Rl)^2
Where:
Rs = system resolution, Rf = film resolution, Rl = lens resolution.
Oly claims that the 4/3 system lenses have double the resolution of 35mm
lenses. Is this necessary for today's cameras or only for the future
4/3 sensors which may be expected to hit 10-12 MP? But a 10-12 MP
sensor doesn't require twice the resolution of a 5 MP sensor. Does that
also imply that a 5 MP sensor is somewhat beyond 35mm lenses?
This one's too hard for me. Anybody? More emprical tests?
Chuck Norcutt
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