I don't think they are obligatory, though they are often used for longish
telephotos to maximise the performance.
I think what happens, at least with Zuikos anyway, is that Olympus says -
well this faster version is going to cost more due to the larger size so
we might as well go to town on it and make it as well as we know how to.
This would possibly explain why the faster Zuiko lenses are that much more
expensive and why they usually have better performance.
Giles
Gregg Iverson wrote:
> Does a faster lens usually also require more exotic materials or
> engineering the way a faster car seems to?
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