Lens optimization is the wrong word to use. No lens manufacturer takes a
lens design and grinding accuracy requirements that would produce a lens
that is diffraction limited at f/1.4 and thinks that by "optimizing" for
f/5.6 or whatever, it would be better at f/5.6. It doesn't work that way.
The resolution and/or acutance of a lens simply becomes more difficult as
the *physical* size of the glass gets larger. Keeping glass figures accurate
to within wavelengths of light is difficult and is made more difficult as
the *Physical* size of the glass increases. This is also compounded by the
number of elements for which the accuracy has to be maintained. Further,
errors that were not seen at f/5.6 begin to show as the aperture increases.
You know, if any manufacturer made a lens that was diffraction limited at
it's fastest stop, I would feel cheated! With just a little more glass to
the same standards, I could have the sharpness the lens has now at the stop
it has now ...and a couple faster and good enough when the light is really
low!
Regards,
Bob...
------------------------------------------------
"A picture is worth a thousand words,
but it uses up three thousand times the memory."
From: "Boris Liberman" <[EMAIL PROTECTED]>
Recent talk about 28/3.5 and 16-45 zoom performance got me confused.
My (probably very much Boris-the-average) belief was that most lenses
are optimized at 3 or so stops from their widest aperture. So, for
most f/2.8 lenses it would be f/8 or thereabouts.
Is it right thing to assume? Or there is something quite basic that
escapes me?
Unconfuse me, will you please? :)
