DOF & leaf shutters

[T3D Peter Abrahams <telscope@xxxxxxxxxx>]

While searching my files for depth of field, I found this very interesting
post, which I regretfully send to this list without author's permission.
The optics of old lenses have been under discussion, but the shutters could
also have an effect.  I can see where the action  of a leaf shutter is
somewhat similar to apodization.  But in this case you have all the edges
of the leaves for light to diffract off of.  Comparing a round aperture to
a star shaped aperture, the latter would seem to have much worse
diffraction.  Also, the effect on the out of focus image is unclear to me.
Any comments?

" Incidentally the slow rise and decay time of leaf shutters produces
a more attractive and clearer out of focus image and more apparent depth of
field
than a shutter which opens and closes instantly such as a focal plane
shutter. Some point and shoot cameras, Minolta unless my memory fails me,
used this priciple of sluggish shutter called "apodization" to improve
resolution  some years back . Telescope mirrors are often "apodized" by
having the mirror coating not end abruptly but fade out gradually at the
edges of the glass. This effect may be well employed by experimental stereo
people who need lots of depth too..   ED ROMNEY"

_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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