[rollei_list] Re: Who uses a T as a 'daily driver'
- From: Marc James Small <marcsmall@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 02 Feb 2010 16:29:35 -0500
At 02:14 PM 2/2/2010, Eric Goldstein wrote:
Hi Marc -
Relative to the ideal design speed for a lens
type.. If the lens was well designed and
executed at it's idea design speed, then it will
(by definition) be best wide open. The lens to
which you refer was not... it was designed as an
f/2.8 lens while the type's idea speed is
f/4-4.5. As such, it will likely not reach best corrections until f/5.6-6.3
Eric
Argue with the designers. They designed the
recomputed Tessar to have its best performance at
f/4 to f/5.6. This is really well documented and
there is extensive literature on the point. Bear
in mind that Zeiss was terribly proud of the
performance of the Recomputed Tessar, and for a
reason: the Tessar was designed by Paul Rudolph,
who never got it to work well at large
apertures. He assigned the task to his
assistant, Ernst Wandersleb, who devoted his
career to producing a workable Tessar at
f/2.8. He never quite made it, but he certainly
improved the breed. He, in turn, passed the
torch to HIS assistant, Hans Sauer, who
accomplished this with the Recomputed Tessar. It
took seventy years and three lifetimes, but they made it.
From 1892 until 1957, the idea was to produce a
Tessar which would operate reasonably well at
f/2.8 and which would produce its optimum performance at f/4 or f/5.6.
I'm not a REAL optical engineer, Eric: I just play one on television ...
Marc
msmall@xxxxxxxxxxxx
Cha robh bàs fir gun ghràs fir!
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