"Jeremy" <jeremy@nospam.thanks.com> wrote in message news:1dFFb.9246$wL6.702@newsread1.news.atl.earthlink.net...

> x-no-archive: yes

> "David Ruether" <rpn1@no-junk.cornell.edu> wrote in message

> news:PQEFb.12$7S6.7@nwrdny02.gnilink.net...

[...]

> >For me, distant

> > subject info MUST be sharp in a "landscape" or an "architectural"

> > image - and the "almost-sharp" of stretched-DOF-covered images

> > looks bad.

[...]

> I remember seeing Carl Zeiss chart that showed the effect of diffraction at

> various f-stops. Once you go beyond f/8, as I recall, the number of lpm

> drops off significantly. So, stopping down for maximum DOF has a price, in

> terms of reduced sharpness. Unfortunately, this trade-off is not apparent

> just by viewing the scene in depth-of-field-preview.

Yes, though limiting apertures to f8 minimum is more limiting than necessary,

since diffraction effects are not very bad (or observable in prints) for 35mm

until somewhat past f11. While with a good lens of 50-90mm or so, the

resolution in the center may peak around f4-5.6 (and at the edges maybe a

stop smaller), the losses due to diffraction do not generally soften the image

appreciably even at f16 (though I avoid f22-32, except for high-magnification

macro work). With landscape work, it is necessary for the fine distant detail

to be sharply-rendered (this is more important than having the larger-scaled

nearer material technically equally sharp in setting up the focus distance for

best DOF) - nothing looks worse to me than soft landscape photos (unless

intended) resulting from use of too small a stop, or from poor choice of

focus distance (using DOF scales and tables results in this, unless the guides

for focus distance and aperture are modified...).

> On the other side, opening the lens up to max or near maximum aperture often

> results in softening, especially at the edges. So there is a relatively

> narrow range of f-stops that will yield an image that is both sharp and does

> not sacrifice lpm resolution on the film. Maybe 2 stops, if that????

>

> Decisions, decisions . . .

Top-class non-zoom lenses in the 50-90mm range for 35mm are sharp

from wide-open to about f16, with the peak near the middle; lesser lenses,

ones significantly different in FL (especially super-wides), or zooms may

have much more restricted ranges of stops for good performance.

Good super-wides may perform really well only at f11-16; many good

zooms that include the WA range may perform well only at f8-16;

lesser-quality lenses away from the 35-135mm range may have no

really good stops at all. While it is fun to use the best lenses at only their

best stops, often in reasonable-sized prints the visual differences in the

prints between this stop and one with 1/4 or so less resolution may be

minimal (and would preclude using the lenses wide-open, which can

result in wonderful images...). Given the above, though, it is still amazing

how much better the image will look if shot with a significantly larger

format camera - the advantages in tonality can show easily, even if the

print unit resolution may not be much different...

--

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com