In article <33375304.B18@flash.net>, wesch@flash.net says...

>Is is true that lenses have an aperature that is sharper than the
>others? If so, does anyone know what it is for a Hasselblad 150?

Amazing....!;-) Yes, middle stops on virtually ALL lenses are
sharper (higher resolution and contrast), though the best
lenses extend the relatively good range toward wider stops...
Simple stopping down helps correct several abberations (and
lens makers generally wisely choose not to expend the kind of
resources required to fully correct lenses at the widest stops
[you would not be able to pay-for/lift/pack the resulting lenses,
if fast]), but simple stopping down also reduces the theoretical
limits of optical performance due to diffraction. As a result,
most lenses improve as they are stopped down toward f5.6-8 or so
(wide angles and zooms may require smaller stops to peak corner
performance [often f16-22...]), level out somewhat through f8-16
(though there will still be a best stop, usually f8 or f11), with
declining performance with further stopping down. With 35mm, the
smallest good stop is about f16; for medium format, f22; for
large format, f32 (determined by image magnification - the actual
resolution will be the same for all formats at small stops, since
diffraction is the limiting factor [barring lens defect]).
BTW, due to the modest angle of view and magnification, short
teles (and short tele zooms...) are the easiest FL's to make sharp
at wide stops, and moderate-aperture short teles can be excellent
to the corners wide-open (as can expensive wide-aperture short teles).
Normal lenses can also be fast and excellent, but often compromise
wide-aperture corner performance for economic/practicality reasons.
Wides usually require considerable stopping down for best overall
performance, though they can be excellent over almost all of the
frame at medium stops (fisheyes are easier to design, and can combine
extremely wide angle of view with excellent performance at middle
stops). Expensive, special-glass teles are generally fine, even
wide-open. Zooms are "convenience" lenses, and the bulk of them
are not very good (compared with primes), though there are notable
exceptions.
Since image resolution is a result of the interaction of both lens
and film resolution, lens resolution variation is leveled some when
imaged on film (the difference between the best and worst lens
resolution is narrowed in the film image). Doubling either the
film resolution or the lens resolution does not double the resultant
film image resolution (which will be much less than either the film
or lens resolution alone). (This saves cheapo lens makers from
bankruptcy, but, alas, does not reward the makers of truly excellent
glass sufficiently...;-) - but it does provide for fairly consistent
on-film image quality when using wides, normals, teles, and even
zooms at a variety of stops.)
Hope This Helps