A stupid question: sharpness/resolution vs focus

Started Nov 27, 2005 | Discussions
Gediminas 8 Senior Member • Posts: 1,133
A stupid question: sharpness/resolution vs focus

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?

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

Enlightenment would be appreciated:)

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beerguy Senior Member • Posts: 2,539
Re: A stupid question: sharpness/resolution vs focus

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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bg

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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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karl vollmers Regular Member • Posts: 389
A second stupid question

So given that diffraction is a problem with small apertures. How did the A. Adams and others in the f-64 crowd do it or deal with it?

beerguy Senior Member • Posts: 2,539
Re: A second stupid question

karl vollmers wrote:

So given that diffraction is a problem with small apertures. How
did the A. Adams and others in the f-64 crowd do it or deal with it?

I'm not sure how often they actually shot at f/64. The f/64 Group was dedicated to images that were sharp from edge to edge. A lot of that can be accomplished with camera movements (law of converging planes), which allows you to stop down a bit less. OTOH, the lenses they used back then were probably not as razor sharp as today's glass, and diffraction was less noticeable. Or they were willing to take the hit from diffraction to get maximum DOF. On a 8x10 contact print, it may not even be noticeable.

I looked at my collection of LF glass, and most stop down to f/64. One, my Nikkor 450M, stops down to f/128. However, it starts at f/9. I can't recall ever having stopped down past f/32, and f/22 is more typical. (Most LF lenses specify the image circle at f/22, so if you are using extreme camera movements, you need to stop down to at least f/22 to prevent vignetting.)

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karl vollmers Regular Member • Posts: 389
f/64 macros

I've seen some flower macro's shot with LF stopped down to f/64, then blown up to a meter square. they were amazing.

Clemens B. Regular Member • Posts: 173
Re: A second stupid question

did the A. Adams and others in the f-64 crowd do it or deal with it?

They had way larger CoC than our smallish 16MP/24*36 Chips today, I think it didn't affect their regular prints much.

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Clemens Bauer

OP Gediminas 8 Senior Member • Posts: 1,133
Re: A stupid question: sharpness/resolution vs focus

beerguy wrote:

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 partly agree on the horizon part. On the other hand, not all tripods are equipped with spirit levels, which means there's little or nothing to be gained in that respect from using one.

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.

Where did I say that it's bad? I love mine:) I was only referring to the effect of diffraction on resolution (of any lens) - in the case of the 10-22, the effect has been found to surface from f8 upwards (see http://www.photozone.de/8Reviews/lenses/canon_1022_3545/index.htm ).

A detailed explanation here:

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

Thanks for the link. However, it doesn't quite answer my question, which was: if diffraction deteriorates the sharpness of a lens, is there any point in using the lens for landscape work, say, at f16? The positive and negative effects of a stopped-down aperture would seem to cancel each other out.

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OP Gediminas 8 Senior Member • Posts: 1,133
What do current ≤35mm pros do then? (nt)

Clemens B. wrote:

did the A. Adams and others in the f-64 crowd do it or deal with it?

They had way larger CoC than our smallish 16MP/24*36 Chips today, I
think it didn't affect their regular prints much.

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Petteri Sulonen Forum Pro • Posts: 24,585
Re: A stupid question: sharpness/resolution vs focus

Actually, most "serious" landscapers I know rarely stop past f/11 if they're using 35 mm. OTOH few really "serious" landscapers I know are using 35 mm, they tend to prefer medium-format or view cameras, although some have gone for FF digital lately.

But yeah, if you stop down past the diffraction limit, you will be sacrificing resolution for depth of field. That's why they don't, unless they really want the DOF.

As to the tripod, it'll make a difference even if you're not shooting at f/22... unless you're shooting in the noonday sun, which very few "serious" landscapers do on a regular basis.

(Why am I again reminded of cousin Angus and sugar on porridge...?)

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beerguy Senior Member • Posts: 2,539
Re: A second stupid question

Clemens B. wrote:

did the A. Adams and others in the f-64 crowd do it or deal with it?

They had way larger CoC than our smallish 16MP/24*36 Chips today, I
think it didn't affect their regular prints much.

The thing I find interesting regarding CoC is that even in 4x5, the CoC is sized based on an 8x10 print, the same as in 35mm. So the DoF calculators found on some LF cameras, like Sinars, are based on this number. Standard advice is, if you want to go big with your images, use the calculator, and close down at least one more stop.

I haven't shot my LF stuff much in recent years, but I'm getting the urge to break it out. I hate lugging it around, but nothing else comes close to LF when it comes to holding detail. I find myself sometimes disappointed with the detail in digital images. I know it's because I'm spoiled by LF images - grain-free 30"x40" prints are incredible. I mostly shoot landscapes, and LF is really the way to go if you want the detail that caught your eye to begin with. Cost of film and processing can really hurt, though - it's on the order of $5-$6 per 4x5 frame.

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beerguy Senior Member • Posts: 2,539
Re: A stupid question: sharpness/resolution vs focus

Gediminas 8 wrote:

beerguy wrote:

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 partly agree on the horizon part. On the other hand, not all
tripods are equipped with spirit levels, which means there's little
or nothing to be gained in that respect from using one.

For landscape work you should be using some sort of level, at a minimum the small spirit level you stick in the cameras hot shoe.

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.

Where did I say that it's bad? I love mine:) I was only referring
to the effect of diffraction on resolution (of any lens) - in the
case of the 10-22, the effect has been found to surface from f8
upwards (see
http://www.photozone.de/8Reviews/lenses/canon_1022_3545/index.htm ).

Looking at the test data, the diffraction effects seem to be fairly minimal. I wouldn't expect to see much impact on image quality, at least in a print. Pixel peeping is another story.

A detailed explanation here:

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

Thanks for the link. However, it doesn't quite answer my question,
which was: if diffraction deteriorates the sharpness of a lens, is
there any point in using the lens for landscape work, say, at f16?
The positive and negative effects of a stopped-down aperture would
seem to cancel each other out.

It just a matter of finding the sweet spot for a given lens. If the lens starts to exhibit diffraction at f/8, then maybe you only stop down to f/11, and then only when needed. I typically shoot between f/8 and f/11 with most lenses anyway, unless I'm looking to blur out the background. Sometimes I shoot at f/16, but only if necessary. And I suspect that you would be hard pressed to see diffraction effects in a print, anyway. Many things that can be found on an optical bench are not really noticeable in real shooting situations.

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bg

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OP Gediminas 8 Senior Member • Posts: 1,133
The answer I was looking for - thanks (nt)
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