Is Focus relative?
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View Poll Results: Is focus relative?
Focus is absolute, never relative to anything. 1 16.67%
Focus is relative to the exhibit/display environment 5 83.33%
Voters: 6. You may not vote on this poll

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Old 1 Week Ago   #1
Vicuna
 
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Default Is Focus relative?

I was told by a member of another forum that

" it's either in focus or not. Focus is not relative......"

I believe that the first part of that statement statement to be true. But whether or not to use the image I believe focus to be very relative to the end use and presentation / exhibit. For instance, If the image is to be displayed as a small image with little magnification or at an abnormally long distance in comparison to the print size...Is focus still not relative? I believe it becomes very relative.

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Old 1 Week Ago   #2
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Default Re: Is Focus relative?

`


EVERYTHING is relative, except
acoarst the speed of light

OTOH, anyone pondering such a
question needs to know, or learn,
the basics of circles of confusion.

As to the line " it's either in focus
or not. Focus is not relative......"
,
thaz a pointless meaningless thing
to preach. There's no such condition
as " in focus ". Yes, it's common-use
photo jargon, but happens to be too
vague for arguing about. Something
can be "focused" ... and can be very
focused, badly focused, etc. But "in
focus"
is meaningless.



`
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Old 1 Week Ago   #3
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Default Re: Is Focus relative?

Inherent in depth of field calculations is the concept of "circle of confusion," which may be defined as the maximum diameter of the blur spot on the image to be considered "in focus." This also presupposes that the ratio of the size of the as-viewed image - usually measured as the diagonal of an uncropped enlargement of the original image - to the viewing distance is held constant. This ratio is typically one or thereabouts, which for an imager of 4:3, translates to a 10 x 7.5 inch enlargement at normal reading distance. For a full-frame image, this translates to circle of confusion of 0.03 mm, which translates to a blur circle of about 0.2 mm for the enlargement to be viewed at normal reading distance. Of course, for an image to be viewed at a correspondingly larger distance, the blur circle may be correspondingly bigger and the image still be considered sharp. Pixel peepers and viewers who break out the magnifying glass when viewing enlargements of this size may not consider a 0.2 mm blur circle small enough, while those viewing the image on a monitor may be able to tolerate an even bigger blur circle.

There are those who would say that a detail is either blurred or not, and these would be those who would say that focus is absolute. However, there is a transition between "can't get any sharper than that" to obviously not sharp, so there is some wiggle room in the transition region. Of course, I voted for "focus is relative."
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Old 1 Week Ago   #4
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Default Re: Is Focus relative?

Focus is a tool, the use of that tool is relative to the desired output. Focus for most photographers is a very close first cousin at the least and may be a closer relative for many. All things in the universe are relative, including the speed of light.

Miles Padgett at the University of Glasgow has as well as physicist at Princeton have shown that the speed of light is not the absolute as once thought.
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Old 1 Week Ago   #5
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Default Re: Is Focus relative?

`


Quote:
Originally Posted by gryphonslair99 View Post
"... All things in the universe are relative,
including the speed of light."

Miles Padgett at the University of Glasgow
has as well as physicist at Princeton have
shown that the speed of light is not the
absolute as once thought.
So .... the warp engines on the Starship
Enterprise are not so far fetched as they
might seem




`
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Old 1 Week Ago   #6
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Default Re: Is Focus relative?

Quote:
Originally Posted by Golem View Post
`




So .... the warp engines on the Starship
Enterprise are not so far fetched as they
might seem




`
In our lifetime they are.
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Old 1 Week Ago   #7
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Default Re: Is Focus relative?

perceived sharpness is absolutely relative. Hence the rules for viewing distances of pictures in galleries and museums and such. True focus however refers to absolute sharpness of details and edges and such at any distance of the unaided eye. And then you get into clarity. Think pointillist paintings and such things where clarity is relative to viewing distance. It's all semantics, and from which vantage you are discussing: the physics of the thing, or the mental subjective. the aided eye, microscope whatever reveals that it is ALL relative to distance.
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Old 1 Week Ago   #8
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Default Re: Is Focus relative?

`



Compared to most of what gets discussed and
the examples offered here, focus IS relative. I
can recommend a comparison that illustrates
just how relative it can be.

If you reeeeeally wanna see a hugely more
powerful example of "absolute" focus, allowing
that everything is relative, but an example so
much closer to absolute than visible light lens
photography, check out some images from the
scanning electron microscopes. Some of the
subject matter is actually not microscopic but
things visible to the naked eye, bug-sized.

What you'll see is deep focus stacking using
electrons rather than photons-and-glass. The
details of why it works are not worth detailing
in this space, but the imagery WILL give you
a whole new standard for "focused"

Examples at:

http://webspace.ship.edu/gspaul/Scan...rthropods.html



`


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