A stupid question: sharpness/resolution vs focus

Started Nov 27, 2005 | Discussions thread
RapidPix Contributing Member • Posts: 917
"sharp"

I'd agree with what you've said, but still suggest that the word "sharp" encompasses more than just "within the acceptable "circle of confusion." Sharpness has to do with focus, blur (or lack thereof), resolution, contrast and a sprinkle or two of fairy dust and gold.

beerguy wrote:

Gediminas 8 wrote:

Hello,

while many lenses are considered to be their sharpest at f/8-11,
others are said to be better at different F numbers due to the
effect of diffraction. For example, the EF-S 10-22 is said to
deliver the highest resolution at something like f/4.5.

However, I have difficulties reconciling this with the fact that
any serious landscape photography is done with lenses stopped down
to f/16 or even f/22 so as to get in focus as much of the image as
possible.

Are folks who use tripods and such small apertures sacrificing
image sharpness for the sake of DOF, ie focus? Should they be using
their wide-angle lenses at f/4.5 and the like and leave their
tripods at home?

I would never leave the tripod at home - no hand-held image is as
sharp as one shot using a good tripod, disregarding IS. It's also
tough to guarantee a straight horizon hand-held.

I find it difficult to believe the 10-22 is that bad-I've used it
and been extemely pleased with the images, and I tend to shoot at
at least f/8.

And - a silly question perhaps - what's the difference between a
"focused" and "sharp" part of an image then?

The "focused" part of the image is what you actually focused on.
The "sharp" part of the image is the portion that is within the
acceptable "circle of confusion", generally 1/30 mm. The only part
of any image that is truly in focus is what you focused
on-everything else is blurred to some extent. The degree of
accebtable blur depends on how much you want to enlarge the
image-more blur is acceptable for a 4x6 print than for an 8x10.

A detailed explanation here:

http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/950/depth-of-field.html

Enlightenment would be appreciated:)

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