Hello Giles,
you wrote
>I have never understood the basis for this urban myth/truism.
>
>For Zuikos at least, the opposite would seem to be the case going by
>discussions on this list and lens tests.
>
>For almost every focal length/zoom range the fastest lens would appear to
>have better performance as far as I can determine:
This urban myth/truism may have to do with the fact, that especially with
long focal length a greater aperture indroduces a greater chromatic
abberation by itself and the optics have to be much better to compensate
this (the relationship between maximum aperture value and chromatic
abberation is an exponential one). With wide angle lenses and great
apertures, for example, the coma must be compensated with more cost. So if
bright lenses are better than their counterparts with smaller apertures,
this results from a general higher cost of their lens designs, which is not
necessary with less bright optics.
Matthias Wilke
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