Yesterday, I finally got around to a little project that I've been putting
off for a while. I wanted to compare resolutions of various lenses at all
F-stops. The primary reason for this little project was determining which
of my primes was the best "walk about" wide-angle to throw on an OM body.
To test this, I used the E-1 and a trusty USAF line-pair res chart taped to
a door. The res chart was printed on a single 8.5x11 sheet of paper
centered on the door, and the picture was of the entire width of the door
with trim on each side. Even with the 24mm lens, my closest distance was
about two meters or so.
I manually metered the doorway and my starting exposure for every lens was
1/30 at F2.8 and I offsetted the exposure all the way down to F16 or
F22--whichever the lens had as the maximum setting. The RAW files were
converted with Olympus Viewer with sharpness set to zero (to minimize
sharpening artifacts and to mimick film's lateral halation tendancies).
The 24/2.8 was obviously soft wide open but would max out the sensor from
F5.6 to F8.
The 35/2.8 was not as soft wide open but would max out the sensor from F5.6
to F11.
The 35/shift was essentially maxing the sensor out from wide open to F11,
but was still usable at F16 and even F22.
The 35-80 at 35mm, essentially maxed the sensor out from wide open to F16.
(Simply amazing)
The 50 macro was soft wide open, but maxed the sensor out at nearly all
apertures except f22.
The 35-80 at 50mm was sharper than the 50 macro wide open, but comparable at
all other apertures.
The 35-80 at 80mm was sharp enough wide open and held it's own throughout
most apertures.
The 100/2.8 was slightly soft at F2.8, but from F5.6 to F11 was stellar. No
idea where the topout point is.
I call this a wasted effort because the limiting factor in these tests was
the sensor. We all know the E-1 is a bit soft, but I still found it
interesting how some of these lenses just slammed the limits of the sensor
and kept going. I will repeat this test with a borrowed E-3 to see if I can
get a little bit more oomph out of the data.
However, it was still a success because i learned once and for all what
apertures to shoot the 24/2.8 at and which to avoid. The 35/2.8 (an ancient
silvernosed lens) was obviously a sharper lens than the 24/2.8 at most
apertures, but the 35/shift slam dunked them both. The 24/2.8 is the one
lens that has flummoxed me through the years as it can either be extremely
sharp or extremely disappointing. I'm beginning to understand why.
The 35-80 is incredibly sharp wide-open, but at the mid-apertures is pretty
much what the other lenses in the same focal length are giving, but this
specific sample is prone to CA and some bulging distortion. Definitely not
an issue for people/event photography (for which it is emmenently usable,
but for static scene pictures, probably not the best lens to grab. The 35-80
does have more contrast than any of the other lenses which is also
contributing to a perceived increase in sharpness.
But, once I retest with a sensor with greater resolution, I'll have a better
handle of what is happening in that zone where the E-1's sensor is maxed
out.
I didn't test the 200/4 or Tokina 100-300/4, because my working distance
would have forced me out the back door and halfway to the
neighbors--besides, I already have a handle on what those lenses are doing
through other controlled tests.
Where I do feel the test was a success was in extrapolating the data for
film usage. The pixel density and AA filter characteristics of the E-1 gives
me a good indication of the sharpness acheivable on the scanned films I'm
using. A quarter-frame crop of a 35mm negative is giving me comparable
sharpness to the 1/4 frame 4/3 sensor.
One thing that mystified me, though. The F22 image in every case was
anywhere from 1/4 to 3/4 a stop too bright. Either the Zuiko's F22 position
really isn't F22 (closer to F16) or the way the digital sensor responds to
light, there is some wierd gain at F22.
AG
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