Hello
(New to the list, my first posting.)
My understanding is, from a purely mechanical perspective, the fewer the
aperture blades, the bigger each blade needs to be (so they can cover
the hole when closed). This means that when *open* the barrel of the
lens must be wider to allow them room to move out of the way. Bigger
blades mean more inertia when opening and closing, but a design with
fewer blades is cheaper to make...
Wide-aperture lenses are likely to have more blades, primarily so that
the barrel of the lens can be kept within reasonable dimensions -- and
size was a primary design objective of the OM system.
About the only advantage for more blades that I can imagine -- apart
from the shape of the out-of-focus highlights -- might be a (measurable)
decrease in diffraction effects at the corners where the blades
intersect. Fewer blades will make more acute angles, more diffraction. A
design with more blades can more accuratly close down to small openings, too.
The Leica lens probably has a lot of blades because it's already quite
big because it did not use a telephoto design (Tessar?, Planar? I dunno)
and price is no concern anyway.
Hope this helps.
Vaughan
> From: "Dirk Wright" <wright@xxxxxxxxxxxx>
>
> I think that the number of blades in a lens is at leasty partly a
> function of the fact that these lenses are for SLR cameras as opposed
> to rangefinder types.
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