[Leica] Performance description

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

Doug wrote:
>Given that english isn't Erwin's primary language some interpretation may
be in order here.  When I say "in >the field" it means, as you apparently
have assumed, "when I'm outside making pictures".  It's possible that >Erwin
means "away from the central part of the image area", which is how I
interpret his report.  Perhaps >Erwin can jump in and clarify for us.

Doug is correct: When I talk about "performance in the field", when
discussing image quality I am using the phrase that is common in optical
discussions: you distinguish generally between performance on axis (or in
the center) and in the field (from angle of field) or off-center.
My usage of these words is not an indication of my capabilities of
expressing myself in English, but a conformation to the technical language
used in most handbooks and test analysis..
I do not like using the wellknown designations: center and corner, because
in fact we have to distinguish between a series of zonal areas expanding
from center (the optical axis) to the extreme corners. Most important for
the assessment of image quality are the image zones located at a distance
from 3 to 9 mm from the center (axis) and these areas are designated as the
field (in German "im Feld"). So we have from center to corners a progression
that is designated radially: center (axis), field, outer zones, corners, or
in distances from center (in millimeters): center = 0, field is from 3 to 9,
outer zones from 12 to 18, corners from  18 to 21mm.

I am sorry there is some confusion between the designation of a field test
(practical shooting) and image performance measured on axis and in the field
(of the lens angle).

In my reports I clearly distinguish between a labtest (with contrast details
on axis and in the field) and a field test, where I state what films I use
and what pictures I take, to supplement my labtest analysis.

Thanks Doug for giving me the opportunity to clarify this topic.

Erwin