On 6/4/2012 6:22 PM, Larry Colen wrote:
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 l...@red4est.com sent from i4est
To a large extent it depends on the lens - I've seen some that benefit
hugely from being stopped down one or two stops and others that show
less of an improvement. My A 50 1.4 benefits form being stopped down, my
FA 50 1.7 is almost as good wide open as it is at f 4 or 5.6. Back when
I had the Rikenon 55MM F1.2 it was noticeably less sharp wide open (and
also had a fair bit of light fall off.) My Tokina 400 f5.6 is not so
sharp at f5.6 but improves tremendously at f8. Most macro lenses I've
tried benefit from stopping down but are very good wide open as well.
What it boils down to (for me) - in theory any lens would benefit from
stopping down one or two stops, but unless I see a difference I don't
worry about it. Stopping down = slow shutter speed or higher ISO, either
of which would probably offset the benefit gained by shooting at the
optimum f stop.
I do notice a loss of sharpness when stopping down to f16 or beyond, I
assume due to diffraction. So, as a general rule of thumb I try to stick
with f8 or at the most f11 . Makes for nicer backgrounds as well. For
general shooting I find f5.6 to usually be fine for DOF. You really just
got to try out your lenses and see what you experience.
MCC
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