[Leica] HiRes Photography (2)

["Erwin Puts" <imxputs@knoware.nl>]

As I have discussed often, you cannot design a lens for high contrast and
low resolution or the other way around: low contrast and high resolution. So
any statement that the early Japanese lenses won the market because they
designed lenses with the hc-lr character misses the point. Still it is true
that the Japanese lenses exhibit often a high sharpness of the main subject
outlines. And a complete loss of fine detail too.
We know that we never get a true infinitesemal small image point on the film
plane. The bundle of rays from the object point may be very narrow at best,
but the true shape of the point around the filmplane is a paraboloid shape
of some longitudinal extension. In the core much light energy is
concentrated, but there is substantial light energy in surroundings areas.
So the choice of the true, physical image plane relative to the true
geometrical focal length determines the reproduction of the image point. Now
my research indicates that you can select a location of the filmplane, such
that the intersection of the bundle of rays favors a broader sectin of the
cone of light, which means high contrast but low resolution. Also it is
possible to select a location that favors the most thin diameter of the
paraboloid, which invariably means high resoltion but soft contrast.
This is just what the Japanese did: their lenses had he same properties as
the German ones, but they choose a different location of the effective film
plane.  They could do this on purose, because of philosphy, but also becaues
they had better glass than the Germans, Hoya and Ohara delivering better
glas than did Schott. With this glass and a different type of aberration
correction (and now I am conjecturing, but with reason), they  could achieve
a better flatness of field, and so could shift the image plane more than the
German designs, which assumed a certain curvature of field and needed a
specific image plane to intersect this curved field.
So the early lenses from Canon, Nikon and Pentax too (among others)
emphasized the rendition of the low spatial frequencies and by selecting a
image plane which again emphasized contrast they achieved the characteristic
definition.
But this approach also gave more latitude in neglecting residual aberrations
and manufacturing tolerances.
Making lenses cheaper etc.
The current emphasis by some that a limit of resolved detail should be based
on what was standard practice in the past, is not tenable. certainly not in
the light of recent improvements by Leica designers, that shifts the balance
to a much higher level of definition of fine detail with high contrast.
That is for part 3 in the near future.
As this part is an excerpt from ongoing research, copyright should be
attached here.
Erwin