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07-23-2015, 12:45 PM   #166
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QuoteOriginally posted by kh1234567890 Quote
The man behind the coat and sunglasses girl refuses to pop into focus.
“One good test is worth a thousand expert opinions.”

Who said that?

07-23-2015, 02:55 PM   #167
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QuoteOriginally posted by Not a Number Quote
Up to 11 or 12 already
I posted on page 3 that it is a futile thread :-)
07-23-2015, 04:15 PM   #168
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QuoteOriginally posted by kh1234567890 Quote
Hmm... No matter how much cropping and chair wheeling I do, a shot like this (apologies for the bad composition) looks the same to this tired old brain and eyeballs. The man behind the coat and sunglasses girl refuses to pop into focus.
QuoteOriginally posted by mohb Quote
All that cropping and resizing does is alter the visual signals we use to measure depth, the actual DOF will still remain what t was when the photo was taken.
Again, use equivalence to understand what is going on here ...

First, there is no such thing as "actual DOF".

Second, assume you crop the inner 50% x 50% part of the original image, i.e., you apply a crop factor of 2. And assume the original image was taken with 50mm F/4.

The cropping then means the cropped image has equivalent shooting parameters of 100mm F/8 (equivalent wrt an uncropped image looking exactly the same on the same camera body).

Now, the DoF of 100mm F/8 is actually shallower than 50mm F/4. And that's no surprise because you magnified the blur at the boundaries of the DoF region (the cropped image needs be magnified more).

This man will never pop into focus, if anything, cropping will make things pop out of focus.

But the same equivalence teaches us that we would have needed to take the original image before cropping at 50mm F/2 if we were after an image looking like 100mm F/4 after cropping.

It may all sound confusing. But only if you didn't fully understand the concept of equivalence.
07-23-2015, 04:18 PM   #169
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QuoteOriginally posted by SpecialK Quote
I posted on page 3 that it is a futile thread :-)
No offense, but that's hardly indicative of any sort of psychic ability.
It's roughly the equivalent of predicting that the sun will rise in the East tomorrow morning.

07-23-2015, 05:18 PM   #170
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QuoteOriginally posted by kh1234567890 Quote
Hmm... No matter how much cropping and chair wheeling I do, a shot like this (apologies for the bad composition) looks the same to this tired old brain and eyeballs. The man behind the coat and sunglasses girl refuses to pop into focus.
You're going in the wrong direction. Cropping reduces DOF.
07-23-2015, 05:49 PM   #171
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QuoteOriginally posted by jsherman999 Quote
If you're willing to achieve a certain DOF at the expense of maintaining a certain perspective.

snip
QuoteOriginally posted by osv Quote
changing perspective is not equivalence.

claiming that equivalence only entails three parameters is not equivalence either, because it ignores perspective and all the rest of the essential parameters.

this discussion just keeps going downhill
Oh - perspective. I thought we were talking about Depth of Field. In that case there really can't be equivalence because there are too many essential parameters to make alike (or reasonably so).

APSc 100mm f/5.6 12 ft *** Near Limit 11.5ft, Far Limit 12.5ft, DoF 0.97ft, Hyperfocal 290.3ft, CoC 0.03
24x36 100mm f/5.6 10ft *** Near Limit 9.52, Far Limit 10.5ft. DoF 1ft, Hyperfocal 193.7ft CoC, 0.02

24x36 100mm f/4 12ft. *** Near Limit 11.5ft, Far Limit 12.5ft., DoF 1.03ft. Hyperfocal 273.7ft., CoC 0.03

etc.

It isn't exact, but it is equivalent. Except it isn't because of the other essential parameters.

But then, if we're only talking about Depth of Field -- Ansel Adams wrote:

"We can achieve critical focus for only one plane in front of the camera, and all objects in this plane will be sharp. In addition, there will be an area just in front of and behind this plane that will appear reasonably sharp (according to the standards of sharpness required for the particular photograph and the degree of enlargement of the negative). This total region of adequate focus represents the depth of field."

Last edited by monochrome; 07-24-2015 at 06:51 PM.
07-23-2015, 07:22 PM   #172
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QuoteOriginally posted by kh1234567890 Quote
Hmm... No matter how much cropping and chair wheeling I do, a shot like this (apologies for the bad composition) looks the same to this tired old brain and eyeballs. The man behind the coat and sunglasses girl refuses to pop into focus.
Your expectations are backwards if you hope he'll "pop into focus" when you crop and enlarge the image.

---------- Post added 07-23-15 at 10:29 PM ----------

QuoteOriginally posted by wombat2go Quote
“One good test is worth a thousand expert opinions.”

Who said that?
Yep, I've certainly never done the simple test of comparing the DoF of a cropped photo with it's original version (when viewed at the same size):

https://www.pentaxforums.com/forums/169-pentax-full-frame/240468-dof-ffs-aps-...ml#post2553553
07-23-2015, 07:31 PM   #173
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QuoteOriginally posted by BrianR Quote
Your expectations are backwards if you hope he'll "pop into focus" when you crop and enlarge the image.
News flash! He's not going to pop into focus no matter what you do.

07-23-2015, 07:34 PM   #174
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Why is this thread even still going?

It's pretty clear that after 12 pages of "discussion", exactly no one on either side has been convinced by the other. Everyone still believes exactly what they did before entering this thread.

The only hope now is to wait for the Pentax FF. After that comes out, and we can unambiguously use the same (Pentax) lenses on both APS-C and FF, maybe, maybe we can get to "closing this argument once and for all" (though probably not even then ).
07-23-2015, 07:34 PM   #175
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QuoteOriginally posted by Parallax Quote
News flash! He's not going to pop into focus no matter what you do.
Make it a thumbnail, say 200 or 300 pixels or so high and view at the same distance (i.e. don't move your eyes 2 inches from the monitor, that's bad for your health). Does he look anywhere near as blurry or out of focus now?
07-23-2015, 08:05 PM   #176
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QuoteOriginally posted by BrianR Quote
Make it a thumbnail, say 200 or 300 pixels or so high and view at the same distance (i.e. don't move your eyes 2 inches from the monitor, that's bad for your health). Does he look anywhere near as blurry or out of focus now?
No, it doesn't look as blurry; but the image has not changed. The apparent difference is a matter of physiology, not physics.
07-23-2015, 09:18 PM - 2 Likes   #177
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QuoteOriginally posted by Parallax Quote
No, it doesn't look as blurry; but the image has not changed. The apparent difference is a matter of physiology, not physics.
The concept of depth of field cannot be discussed without taking into account physiology. The very definition of depth of field includes a human physiology term - circle of confusion. It's the smallest size a person with good vision can distinguish detail; generally agreed to be 0.01 inches viewing an 8x10 print 1 foot away, if I recall correctly. Many people can see finer detail than that definition. My eyes are much worse than normal (-9.5 and -11.5 diopter). So I would tend to say more of a picture is within focus than the average Joe would say.

If you don't want to consider physiology when talking about what is in focus and what is out of focus, then you have to say that only a single infinitesimally thin plane a certain distance from the lens is in focus. Everything behind or in front is out of focus. Without considering physiology, the DOF for any lens at any aperature at any distance with any size sensor is zero. Well, not sure about those Lytro things.

It's the idea of how much in front and behind that perfect focus plane looks "acceptably" sharp which gives meaning to DOF values.
07-23-2015, 09:34 PM - 1 Like   #178
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The silent learners among us

QuoteOriginally posted by Cannikin Quote

It's pretty clear that after 12 pages of "discussion", exactly no one on either side has been convinced by the other. Everyone still believes exactly what they did before entering this thread. .
I'm not so sure about that.

You only see who's posted, you don't see the slient readers who may have followed (and actually read) some links and learned a thing or two.
07-24-2015, 03:35 AM   #179
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QuoteOriginally posted by jsherman999 Quote
The silent learners among us
I'm sure they are just to terrified to comment
07-24-2015, 04:31 AM   #180
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QuoteOriginally posted by Parallax Quote
No, it doesn't look as blurry; but the image has not changed. The apparent difference is a matter of physiology, not physics.
If changing the physical size of an image and how it appears from your point of reference doesn't count as 'changing the image' to you, that's fine, I'm not interested in a semantics argument.
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