How far is "infinity?" - Not a metaphysical query

I have a Canon A580 digital camera. It has a "Landscape" setting that
I suspect focuses on infinity. Not sure about that but I suspect it.

How far away should something be before I tell the camera that it
should focus on infinity? Is 100 feet infinity for this camera? More?
Less? Sometimes I try to take photographs of the Moon, definitely at
"infinity," and I'd like to know if "auto" or "Landscape" is the best
mode for that. At some point I may ask how to keep the full Moon from
overexposing itself, but I'm trying to work that one out on my own
right now.

I ask because the auto focus doesn't always focus on what I want to
capture and I frequently don't have the time to try to coax it into
automatically locking onto what I want to get a shot of.

Daguerreotype type wrote:
I have a Canon A580 digital camera. It has a "Landscape" setting that
I suspect focuses on infinity. Not sure about that but I suspect it.

How far away should something be before I tell the camera that it
should focus on infinity? Is 100 feet infinity for this camera? More?
Less? Sometimes I try to take photographs of the Moon, definitely at
"infinity," and I'd like to know if "auto" or "Landscape" is the best
mode for that. At some point I may ask how to keep the full Moon from
overexposing itself, but I'm trying to work that one out on my own
right now.

I ask because the auto focus doesn't always focus on what I want to
capture and I frequently don't have the time to try to coax it into
automatically locking onto what I want to get a shot of.

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.

"Daguerreotype type" wrote in message
...
I have a Canon A580 digital camera. It has a "Landscape" setting that
I suspect focuses on infinity. Not sure about that but I suspect it.

How far away should something be before I tell the camera that it
should focus on infinity? Is 100 feet infinity for this camera? More?
Less? Sometimes I try to take photographs of the Moon, definitely at
"infinity," and I'd like to know if "auto" or "Landscape" is the best
mode for that. At some point I may ask how to keep the full Moon from
overexposing itself, but I'm trying to work that one out on my own
right now.

I ask because the auto focus doesn't always focus on what I want to
capture and I frequently don't have the time to try to coax it into
automatically locking onto what I want to get a shot of.

Now that you've gotten some theoretical answers, I'll try to give you a
practical one. If your zoom is set to wide angle, you can safely use 50 -
100 feet as "Infinity". As you zoom toward the telephoto end, you need to
think in terms of 200 feet or more. As the other posts implied, you can
calculate the "exact" distance to focus on, but you don't always have a
calculator and formulas handy. Do some test shots and examine the results
for sharpness and you will soon get a practical idea of where to set the
focus.

As for full moon exposure, remember that the full moon is lighted by by the
sun, so basically, you use the same exposure as a sunlit landscape on
earth - maybe a half-stop more. Again, experiment. Keep in mind that as the
moon goes toward crescent, you will have to increase your exposure. There
are some good charts online if you give Google a whirl.

Good luck!

On Thu, 05 Mar 2009 14:17:03 GMT Daguerreotype type wrote:

| I have a Canon A580 digital camera. It has a "Landscape" setting that
| I suspect focuses on infinity. Not sure about that but I suspect it.
|
| How far away should something be before I tell the camera that it
| should focus on infinity? Is 100 feet infinity for this camera? More?
| Less? Sometimes I try to take photographs of the Moon, definitely at
| "infinity," and I'd like to know if "auto" or "Landscape" is the best
| mode for that. At some point I may ask how to keep the full Moon from
| overexposing itself, but I'm trying to work that one out on my own
| right now.
|
| I ask because the auto focus doesn't always focus on what I want to
| capture and I frequently don't have the time to try to coax it into
| automatically locking onto what I want to get a shot of.

Infinity is that point where parallel lines meet.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
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| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

"Daguerreotype type" wrote in message
...

How far away should something be before I tell the camera that it
should focus on infinity?

When a camera is focused on infinity, a point on the subject appears to be a
circle with the same physical diameter as the lens entrance pupil.

Let me explain this in more detail. Suppose you have a camera with a lens
with an 8mm focal length (typical for small digital cameras) that you are
using at f/4. Then the entrance pupil is 2mm in diameter -- the focal
length is f, and f/4 (i.e. f divided by 4, which is what f/4 really means)
is 2mm.

That means that when you focus on infinity, a point on your subject -- at
whatever distance -- is blurred until it looks like a circle 2mm in
diameter. Obviously if your subject is at arm's length, a 2mm blur circle
looks pretty big. Similarly, if the subject is several km away, a circle
2mm in diameter might as well be a point.

Suppose your image is 4,000 pixels across (again, typical for a 12MP digital
camera). If each pixel were 2mm wide, 4000 pixels would be 8000mm, or 8m.
The conclusion, then, is that with such a camera, if you are far enough away
from your subject that your field of view is 8m wide, then the blur circle
that a point forms will still fit within a single pixel.

Hope this helps.

In article , 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
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.

Justin.

--
Justin C, by the sea.

Andrew Koenig wrote:
"Daguerreotype type" wrote in message
...

How far away should something be before I tell the camera that it
should focus on infinity?

When a camera is focused on infinity, a point on the subject appears to be a
circle with the same physical diameter as the lens entrance pupil.

Let me explain this in more detail. Suppose you have a camera with a lens
with an 8mm focal length (typical for small digital cameras) that you are
using at f/4. Then the entrance pupil is 2mm in diameter -- the focal
length is f, and f/4 (i.e. f divided by 4, which is what f/4 really means)
is 2mm.

That means that when you focus on infinity, a point on your subject -- at
whatever distance -- is blurred until it looks like a circle 2mm in
diameter. Obviously if your subject is at arm's length, a 2mm blur circle
looks pretty big. Similarly, if the subject is several km away, a circle
2mm in diameter might as well be a point.

Suppose your image is 4,000 pixels across (again, typical for a 12MP digital
camera). If each pixel were 2mm wide, 4000 pixels would be 8000mm, or 8m.
The conclusion, then, is that with such a camera, if you are far enough away
from your subject that your field of view is 8m wide, then the blur circle
that a point forms will still fit within a single pixel.

Hope this helps.

Interesting way of explaining infinity!

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

Daguerreotype type wrote:
I have a Canon A580 digital camera. It has a "Landscape" setting that
I suspect focuses on infinity. Not sure about that but I suspect it.

How far away should something be before I tell the camera that it
should focus on infinity? Is 100 feet infinity for this camera? More?
Less? Sometimes I try to take photographs of the Moon, definitely at
"infinity," and I'd like to know if "auto" or "Landscape" is the best
mode for that. At some point I may ask how to keep the full Moon from
overexposing itself, but I'm trying to work that one out on my own
right now.

I ask because the auto focus doesn't always focus on what I want to
capture and I frequently don't have the time to try to coax it into
automatically locking onto what I want to get a shot of.

It depends on the lens, but for most common ones, 50 feet is effectively
infinity.

Ron Hunter wrote:
Daguerreotype type wrote:
I have a Canon A580 digital camera. It has a "Landscape" setting that
I suspect focuses on infinity. Not sure about that but I suspect it.
How far away should something be before I tell the
camera that it
should focus on infinity? Is 100 feet infinity for this camera? More?
Less? Sometimes I try to take photographs of the Moon, definitely at
"infinity," and I'd like to know if "auto" or "Landscape" is the best
mode for that. At some point I may ask how to keep the full Moon from
overexposing itself, but I'm trying to work that one out on my own
right now.
I ask because the auto focus doesn't always focus on
what I want to
capture and I frequently don't have the time to try to coax it into
automatically locking onto what I want to get a shot of.

It depends on the lens, but for most common ones, 50 feet is effectively
infinity.

It varies with the focal length, and while 50 feet might
be true for a short focal length, many longer focal
length lenses can't even focus that close!

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

On Thu, 5 Mar 2009 09:25:38 -0800 (PST) Pat wrote:
| On Mar 5, 9:17?am, Daguerreotype type wrote:
| I have a Canon A580 digital camera. It has a "Landscape" setting that
| I suspect focuses on infinity. Not sure about that but I suspect it.
|
| How far away should something be before I tell the camera that it
| should focus on infinity? Is 100 feet infinity for this camera? More?
| Less? Sometimes I try to take photographs of the Moon, definitely at
| "infinity," and I'd like to know if "auto" or "Landscape" is the best
| mode for that. At some point I may ask how to keep the full Moon from
| overexposing itself, but I'm trying to work that one out on my own
| right now.
|
| I ask because the auto focus doesn't always focus on what I want to
| capture and I frequently don't have the time to try to coax it into
| automatically locking onto what I want to get a shot of.
|
| Infinity is where your lens stops moving "out" when trying to focus.

Some lenses will move beyond that point.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |