Re: How far is "infinity?" - Not a metaphysical query
- From: floyd@xxxxxxxxxx (Floyd L. Davidson)
- Date: Fri, 06 Mar 2009 00:46:10 -0900
Justin C <justin.0903@xxxxxxxxxxxxxx> wrote:
In article <49afebe6$0$33225$815e3792@xxxxxxxxxxxxxx>, Don Stauffer wrote:
What is infinity depends on the hyperfocal distance, which in turn is
dependent on relative aperture (f-stop). On some cameras there is a DOF
scale on the focusing scale that shows the near edge of the distance in
focus at a given f-stop. With wide adoption of AF, those scales seem to
be disappearing :-)
Anyway, google "hyperfocal distance." There is a lot on line on the
subject and it definitely relates to your question. If your camera does
not show such a scale, you'll need to get the calculator out and
calculate it.
What has the hyperfocal distance to do with infinity? The hyperfocal
distance is merely the point at which, for a given aperture, the
foreground, subject, and background, are in focus.
Infinity, on the other hand, is the point beyond which, IME, it is not
possible for anything to be in focus (though atmospheric pressure, AIUI
Not quite! It's the point at which nothing can get
*out* of focus by being further away.
Of course, as Don indicated, that has to do with
hyperfocal distance!
can have impact on whether infinity, or slightly nearer/further than
infinity is actually the point at which infinity is in focus).
It is an interesting subject. I don't pretend to fully understand it,
but I do understand the meaning of hyperfocal distance. The two are not
(necessarily) related.
If the lens, for any given aperture, is focused so that
the most distant point that is in focus is just at
infinity, then for all practical purposes the lens is
focused on infinity. Granted that the hyperfocal
distance is at some closer point, and that for some
distance before that the foreground will be in focus.
But the point is that that is the closest distance where
one can focus the lens (at that aperture) and have an
object be at an infinite distance be in focus.
It is also true that one can then move the focus to
extend the point of focus farther away from the film
plane, and as that is done the range of distane over
which the lens is "in focus" narrows. That can be
extended right out to the point where the _closest_
object in focus is right at an infinite distance. Focus
farther than that, and nothing is in focus.
So, where is the infinity focus point for any given lens
at any given aperture? One definition would be *any*
point of focus between where the farthest possible
distant object is just in focus and a focusing point
where that object is the nearest thing in focus.
(Note that most if not all auto focus lenses can focus
past the point of infinity, which allows the AF hunt to
work.)
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@xxxxxxxxxx
.
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- How far is "infinity?" - Not a metaphysical query
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- Re: How far is "infinity?" - Not a metaphysical query
- From: Don Stauffer
- Re: How far is "infinity?" - Not a metaphysical query
- From: Justin C
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