wide angle

"Gordon Moat" wrote in message
...
"J.Scheimpflug" wrote:

I find it odd that the description of that lens mentions the Schneider
S/A
in such a round-about way. Is it, or is it not the Schneider SWA? Do you
know, Gordon? I certaintly cannot tell.


I have yet to see one in person, though a check of the MTF from ALPA, and
then for the similar (same?) lens from Schneider, seems to show no
difference. Perhaps the only real difference is the focus mount, and the
front identity ring. If the MTF is the same for both, what could be
different
in using either?

Is MTF everything? There could be differences in distortion characteristics
or light fall-off.

"Pupillenaberration" sounds like "Pupil Aberration" to me, the presence
of which is vital to a well-designed Biogon/Roosinov type wide angle
lens. I'm not sure that an international convention regarding the use
of a technical term would stick; although it would be nice if the major
optical firms would clean up their act a bit since they are the ones
driving the language downhill.

5 color crossings is alot, especially for such a narrow spectrum, and
even more unusual that the crossings occur at such well-known
wavelengths. In my own design work I've done a few systems with four
crossings over a fairly wide spectrum (e.g. 350nm - 1000nm), but never
with five crossings. In any case, it seems a shame that we now have to
use adjectives like "true" when discussing apochromats.

Brian
www.caldwellphotographic.com

jjs wrote:

"Gordon Moat" wrote in message
...
"J.Scheimpflug" wrote:

I find it odd that the description of that lens mentions the Schneider
S/A
in such a round-about way. Is it, or is it not the Schneider SWA? Do you
know, Gordon? I certaintly cannot tell.


I have yet to see one in person, though a check of the MTF from ALPA, and
then for the similar (same?) lens from Schneider, seems to show no
difference. Perhaps the only real difference is the focus mount, and the
front identity ring. If the MTF is the same for both, what could be
different
in using either?

Is MTF everything? There could be differences in distortion characteristics
or light fall-off.

No, not everything, but not a bad starting point. Schneider also list
distortion, relative illumination, and transmittance on the data sheets of the
latest 47 mm, and the Helvetar. There is no difference on the data sheets from
Schneider between those two lenses.

Unfortunately, the costs are not low for either the 47 mm, nor the Helvetar. I
doubt anyone would get a chance to try them back to back, to really find if
there was any difference. There is likely more sample variation, than a true
difference in optical construction.

Perhaps Schneider would be willing to provide the answer. They might just give
a marketing type of answer, and claim some difference, or they might actually
confirm some of our thoughts.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com