On 2012-06-04 18:22, Larry Colen wrote:
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.
If you're using an F series or later lens, and you put the camera's auto
program into "MTF" mode in the menus (it might be the default), it will
base it's aperture selections on MTF data in the lens' on-board chip.
This is at least Pentax' idea of the best aperture/shutter tradeoff for
the particular lens.
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