Kodak Ektar 127mm lens

"Neil Purling" wrote


The acid test [of my lens] would be a shot of a brick wall,
taking care to mark the wall with the aperture in use.

I have found a large sheet of newspaper (The Times) makes a
very good quick and easy test target.

I often cut up a good black and white picture
from a glossy magazine and paste the pieces in the center
and corners of the frame. Examining the pictures
dots under high magnification is a good test of lens
resolution.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.

Most of these sort of lenses are lousy 6 ft or less so the target has to be
something at normal taking distance. I think a wire fence would also work,
but a brick wall is usually flat & you can see how sharp the mortar joins
are.

"Neil Purling" wrote in
message ...
Most of these sort of lenses are lousy 6 ft or less so the
target has to be
something at normal taking distance. I think a wire fence
would also work,
but a brick wall is usually flat & you can see how sharp
the mortar joins
are.

That is quite a statement! I haven't found it true. Kodak
Ektars hold their corrections very well down to nearly 1:1.
Zeiss Tessars also work well close. Actually, six feet is
"normal" distance for general photography. Most general
purpose lenses, which are 'optimised' at infinity are
actually optimum at something like twenty to fifty times
focal length to get a compromise over a wide range of
distance.
The "optimum" comes from the fact that its not possible
to correct a lens for both spherical aberration and coma at
more than one distance. Usually, coma is the aberration
which becomes apparent at other distances. Since both
spherical and coma vary with the stop stopping down will get
rid of them in a reasonably well corrected lens.
Most of the lenses used on press cameras are very good.
The requirement was for very sharp images virtually anywhere
in the field and for lack of focus shift, a necessity where
rangefinder focusing is used. The poorest performers are the
Wollensak Raptar, also sold as the Graflex Optar. These, in
my experience, have excessive coma for some reason although
they are very sharp in the center of the field and have
virtually no focus shift. However, an F/4.5 Ektar or Zeiss
Tessar will be free of coma at around f/8 to f/11 where the
Raptar/Optar must be stopped down to f/22 or even smaller.


--
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Richard Knoppow
Los Angeles, CA, USA