I think you should have some more coffee and rethink your position. :-)
Chuck Norcutt
Ken Norton wrote:
> One issue that I'm choking on is that the calculations for diffraction
> limitations are not accounting for asperical element lens designs. A modern
> lens is almost always utilizing aspherical elements which do not expand the
> diameter of the airy disk in a linear manner. You can see this very clearly
> when comparing bokeh of one lens to another lens even though they are the
> same focal length and the subject-sensor distance remains the same.
>
> I have said repeatably that modern lenses seem to have a "zone of focus" vs
> a "plane of focus". For example, a classic, old 50/1.8 may have a plane of
> focus only two centimeters thick at 1 meter subject-film distance, but a
> modern zoom may have that plane of focus that is effectively four or five
> centimeters thick. If the optical engineers have been able to accomodate
> this, it is entirely possible that they've "gamed the system" to exceed the
> theoretical limits of diffraction.
>
> A classic lens design is pretty straight-forward. Especially so if the lens
> is symmetrical. However, newer lenses are actually extremely different. For
> example, that symmetrical 50mm lens is truely a 50mm lens front to back.
> But a modern lens (zoom or fixed) could actually be a 100mm lens with a 1/2
> multiplyer mechanism to give an effective 50mm focal length.
>
> Now, imagine with me a lens design that is, say 50mm, but has
> the diffraction characteristics of a 100mm lens. I believe this is exactly
> what the optical engineers have been able to do.
>
>
> Ken Norton
> ken@xxxxxxxxxxx
> http://www.zone-10.com
>
>
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