Re: Matching lenses - distortion/Digression

[Eric Goldstein <egoldste@xxxxxx>]

Greg Erker wrote:

>   Back in my insomnia days I found that
> the Rikenon (tessars) lenses aren't perfectly
> flat field so one has to choose whether
> to have the center or the edges in focus
> when projecting the flat test slide on
> a flat wall. Focusing with the center seems
> easiest.


To digress a bit and raise a question...

Most Tessars (and Triplets for that matter) are niether flat field or
distortionless. (I say most because I know for a fact that there were
flat field/virtually distortionless process Triplets shortly after the
lens was invented, though they were slow and had a narrow angle of view;
this may well be true for Tessar-types as well.)

This characteristic is actually quite celebrated by many lensmakers,
because it is thought that a certain amount of these abberations give
three dimensional objects a certain roundness and plasticity when
projected onto two dimensional film. Some lens manufacturers (such as
Zeiss and Leitz BTW) purposefully retain a small amount of field
curvature and distortion in some of their modern designs to make lenses
which make pleasing images of real-life subjects.

Does this help the stereo photographer? Or should we treat optical
abberations with the same distain as we view non-orthoscopic stereo
production and viewing?  :-)  Supposedly, the makers of 50's stereo
equipment purposefully retained a certain amount of stretch in their
systems to enhanse the stereo effect, or so claims the Morgan and Lester
Realist Manual... what about lens distortion?


Eric G.