Larry's ideas:
I was thinking about my quest for sharpness, and was considering
trying to do some research into what the aperture "sweet spot" is for
each lens, and was wondering if anyone had already made a chart of
them.
Then I wondered how much it really matters. I've heard "a couple of
stops down from wide open", "anywhere between f/8 and f/16", and a
couple other rules of thumb. I do know that on some lenses,
particularly the FA50/1.4, that stopping it down a couple of stops from
wide open, makes a huge difference. And I suspect that if you look on
an MTF chart, you might be able to easily see the difference between
f/4 and f/8, but is there a practical noticeable difference?
There is also the question of sharpness at the critical focus
distance, and overall sharpness. That a lens might be sharper at f/4
than f/16 at the focal distance, but with a lot more depth of field,
more of the photo will be sharper at f/16, than at f/64.
I'm primarily interested in answers based on personal, practical
experience, rather than theory. My hunch is that as long as I'm not
too close to wide open, or pushing diffraction limits, optimizing
aperture for sharpness is not the most productive place to spend my
time and energy. That I'm generally best optimizing the aperture for
the picture, and not trying to optimize the aperture for MTF.
--
Larry Colen lrc at red4est.com sent from i4est
Larry, I'd consider both sharpness and DOF when choosing the aperture
for one particular pic.
Manual focus, f/8 at 2m with the wide part of the 18~55 has given me
the fastest AF in town. It also has improved sharpness across the frame.
Using the fixed 50s I see a strong diff as I go from wide open to f/5.6
- but then I often want less focus on the background and accept less
sharpness.
My old SMC Takumar 135 f/2.5 is soft open and gets very sharp from 5.6
to 11.
I checked MTF charts / pratical resolution tests of lenses, and did my
own over the years. Some of my results did go against others, but all my
lenses are softer wide open than at some other point, both in the tripod
against some target and in the real world. Knowing what to expect at any
particular setting is useful, IMHO.
From memory, some lenses got sharp faster - close to wide open - and
two in particular needed to be closed a lot to behave - an ancient
Tokina 28-85 and Sigma's 24mm (first version).
--
luiz felipe
luiz.felipe at luizfelipe.fot.br
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