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[OM] More on lens resolution

Subject: [OM] More on lens resolution
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Mon, 18 Apr 2005 14:12:31 -0400
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

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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