Re: Diffraction, F stop, and lens length

[Lon Williamson]

It may explain why some longer non-Macro Pentax lenses
stop down to f32, though.  The M200 f4 and K135mm f2.5
both do.  Anything shorter I own, except for macro lenses,
has a maximum of f22.
What I understand from the posts so far, and thanks folks,
is that _probably_ a 20mm at f22 is affected more by diffraction
than a telephoto at f22.
Now I can sleep at night.       -Lon
Bob Blakely wrote:
This is certainly correct, but the effect is miniscule except for the most
extreme wide angles.
From: "graywolf" <[EMAIL PROTECTED]>
Wouldn't be that simple, would it?
The way I interpret it (and I may be wrong, after all I used to think it
was 
just aperture), it is more a combination of aperture and angle of view
that 
affects diffraction. So you can use f-stop only as an approximation, but
that
ought to be close enough for most work.
In other words a 100mm lens at f22 on a 35mm camera has slightly less
diffraction than a 100mm lens at f22 on a 6x9 camera does. Of course that
is
more than offset by the higher magnification needed with the 35mm image.
So, go ahead and use f-stop. With your istD the sensor resolution is
probably
below the diffraction level at the smallest f-stop anyway, in which case
you can
ignor diffraction.

Steve Desjardins wrote:
Let me see if I have this straight:
The extent of diffraction is determined by the size of the aperture but
the effect at the film plane also depends on the focal length of the
length.  Because both of these are involved, the property I should worry
about in terms of effect on my pictures is f stop, which is the ratio of
these two factors.
Yes?