how close is infinite focus?

I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

Depends on the lens. Bear in mind that the greater depth of field because of
the smaller than film sensor makes it almost moot if you are out of doors.


"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

You are right that the autofocus in a digicam doesn't work on a featureless
field. It would certainly work to set the focus at infinity at an air show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

You are right that the autofocus in a digicam doesn't work on a featureless
field. It would certainly work to set the focus at infinity at an air show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

You are right that the autofocus in a digicam doesn't work on a featureless
field. It would certainly work to set the focus at infinity at an air show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

"Marvin Margoshes" wrote in message
...

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

You are right that the autofocus in a digicam doesn't work on a
featureless
field. It would certainly work to set the focus at infinity at an air
show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

Use the "sports" scene mode. With most cameras that allows the autofocus to
lock on to a moving subject.

(sorry if this has already been suggested... I haven't caught up on this
group in a while.)

"Marvin Margoshes" wrote in message
...

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

You are right that the autofocus in a digicam doesn't work on a
featureless
field. It would certainly work to set the focus at infinity at an air
show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

Use the "sports" scene mode. With most cameras that allows the autofocus to
lock on to a moving subject.

(sorry if this has already been suggested... I haven't caught up on this
group in a while.)

On Mon, 9 Aug 2004 11:41:26 -0400, "skymuffins"
wrote:


"Marvin Margoshes" wrote in message
...

"Lazarus Long" wrote in message
...
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show

You are right that the autofocus in a digicam doesn't work on a
featureless
field. It would certainly work to set the focus at infinity at an air
show
or a fireworks display.

You had a good learning experience. The quick feedback with a digicam is
going to help you to learn more.

Use the "sports" scene mode. With most cameras that allows the autofocus to
lock on to a moving subject.

(sorry if this has already been suggested... I haven't caught up on this
group in a while.)


Good suggestions - sports mode or simply infinite focus. I've also
thought about the cameras "landscape mode" too.

But my basic question still stands - how close is "infinite focus"? I
know aperture plays a role in apparent sharpness, but focus is focus.

In article , Lazarus Long
writes
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

The cute answer is that "infinity focus" is focussed on things
infinitely far away.

The helpful answer - though it may not seem like it - is this. When your
camera is focussed at infinity, objects considerably closer than this
will appear to be sharp. (This is because the amount of "fuzziness" -
the diameter of the circle of confusion - is too small to be seen). The
bad news is that the limit (i.e. how close they get and still appear
sharp) depends on the aperture of your camera lens, and its focal
length; it also varies according to what you propose to do with the
picture (small web picture to huge enlargement - they have different
demands on sharpness). This zone for which objects appear sharp is known
as depth of field (DoF).

With 35mm film cameras, it is easy to find tables (in books, on the web
etc) which will tell you DoF details for any common focal length. For
example, my 50mm f/1.4 lens shows that at f/22 I might expect everything
from 3m to infinity to be in focus at the infinity setting.

With lenses of longer focal length, the DoF for any lens aperture gets
very much smaller; conversely, for wide angle lenses, it is larger. Thus
if you take a portrait with a long lens at wide aperture, DoF is so
small it is often impossible to get both eyes in sharp focus unless the
subject is dead square to the camera. OTOH, if you use a very wide lens
for a landscape at f/16, you can often get everything from a rock 1m
away to the distant mountains in sharp focus.

There is a slightly better way than setting the camera focus at
infinity, and that is to set it (in my above example with the 50mm f/1.4
lens) to focus at 3m, then everything from about 1.5 m to infinity
should be sharp. This setting is called the "hyperfocal distance". For
any lens, at any particular aperture, there is such a setting which
gives you maximum DoF, from about half the hyperfocal distance to
infinity.

Unfortunately, because these numbers are different for every focal
length of lens and every aperture, I can't tell you what they are. You
will have to do some research yourself, either to work it out (the maths
is not that difficult) or to find a suitable table.

One cautionary word: whilst you may be used to seeing the focal lengths
of the lenses of digital compacts being quoted as "35mm equivalent"
numbers - e.g. 35 - 135 or 28 - 80mm - these are a complete trap for
this purpose. You will have to use the actual focal length of the lens,
and the real sensor size, to do the maths.

In the end, it may be easier to find the answer empirically. Even if you
calculate or find a figure, you still have to test it - it will vary, as
I said above, with the use to which you will put the pictures. So, set
the camera to manual, find some regularly spaced objects (lamp posts or
telegraph posts spring to mind) and get to it. You will find a setting
which will work well for your purpose. I'd guess 20m at f/8 will be fine
- but please come back and tell us yea or nay.

At least (being digital) it will be quick and cost nothing except your
time.

BTW - I don't want to rain on your parade, but I would imagine that
digital compacts are about the worst possible type of camera for air
displays. The shutter lag would make it impossible to catch the critical
moment and the focal length at the longest end inadequate for any but a
large formation. If you can't afford a DSLR, a film SLR (with a zoom up
to at least 300mm) would give much better results at reasonable price.

David
--
David Littlewood

In article , Lazarus Long
writes
I'm a relative newbie to most of the features of a "modern" camera.

My question is about focusing - how close, is infinite focus. My
camera is a Coolpix 5400. 20 feet? 30 feet?

I was at an air show this past weekend. With my film camera I would
have simply twisted the lens to the infinite focus and left it there.
However, with this new digital autofocus, I let the camera pick the
focus. Well, for a lot of the shots of the planes overhead, they're
not that well focused. I wrongly thought the camera would
automatically go to infinite focus. So after looking around a bit
(including the manual) I note that AF systems are confused by
relatively featureless backgrounds (sky). So if I had manually set
infinite focus, how close to the camera would something appear to be
in focus?

The cute answer is that "infinity focus" is focussed on things
infinitely far away.

The helpful answer - though it may not seem like it - is this. When your
camera is focussed at infinity, objects considerably closer than this
will appear to be sharp. (This is because the amount of "fuzziness" -
the diameter of the circle of confusion - is too small to be seen). The
bad news is that the limit (i.e. how close they get and still appear
sharp) depends on the aperture of your camera lens, and its focal
length; it also varies according to what you propose to do with the
picture (small web picture to huge enlargement - they have different
demands on sharpness). This zone for which objects appear sharp is known
as depth of field (DoF).

With 35mm film cameras, it is easy to find tables (in books, on the web
etc) which will tell you DoF details for any common focal length. For
example, my 50mm f/1.4 lens shows that at f/22 I might expect everything
from 3m to infinity to be in focus at the infinity setting.

With lenses of longer focal length, the DoF for any lens aperture gets
very much smaller; conversely, for wide angle lenses, it is larger. Thus
if you take a portrait with a long lens at wide aperture, DoF is so
small it is often impossible to get both eyes in sharp focus unless the
subject is dead square to the camera. OTOH, if you use a very wide lens
for a landscape at f/16, you can often get everything from a rock 1m
away to the distant mountains in sharp focus.

There is a slightly better way than setting the camera focus at
infinity, and that is to set it (in my above example with the 50mm f/1.4
lens) to focus at 3m, then everything from about 1.5 m to infinity
should be sharp. This setting is called the "hyperfocal distance". For
any lens, at any particular aperture, there is such a setting which
gives you maximum DoF, from about half the hyperfocal distance to
infinity.

Unfortunately, because these numbers are different for every focal
length of lens and every aperture, I can't tell you what they are. You
will have to do some research yourself, either to work it out (the maths
is not that difficult) or to find a suitable table.

One cautionary word: whilst you may be used to seeing the focal lengths
of the lenses of digital compacts being quoted as "35mm equivalent"
numbers - e.g. 35 - 135 or 28 - 80mm - these are a complete trap for
this purpose. You will have to use the actual focal length of the lens,
and the real sensor size, to do the maths.

In the end, it may be easier to find the answer empirically. Even if you
calculate or find a figure, you still have to test it - it will vary, as
I said above, with the use to which you will put the pictures. So, set
the camera to manual, find some regularly spaced objects (lamp posts or
telegraph posts spring to mind) and get to it. You will find a setting
which will work well for your purpose. I'd guess 20m at f/8 will be fine
- but please come back and tell us yea or nay.

At least (being digital) it will be quick and cost nothing except your
time.

BTW - I don't want to rain on your parade, but I would imagine that
digital compacts are about the worst possible type of camera for air
displays. The shutter lag would make it impossible to catch the critical
moment and the focal length at the longest end inadequate for any but a
large formation. If you can't afford a DSLR, a film SLR (with a zoom up
to at least 300mm) would give much better results at reasonable price.

David
--
David Littlewood