Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Digital Photography > how close is infinite focus?

Reply
Thread Tools

how close is infinite focus?

 
 
Lazarus Long
Guest
Posts: n/a
 
      08-09-2004
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?
 
Reply With Quote
 
 
 
 
Gene Palmiter
Guest
Posts: n/a
 
      08-09-2004
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" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> 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?



 
Reply With Quote
 
 
 
 
Marvin Margoshes
Guest
Posts: n/a
 
      08-09-2004

"Lazarus Long" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> 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.


 
Reply With Quote
 
skymuffins
Guest
Posts: n/a
 
      08-09-2004

"Marvin Margoshes" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "Lazarus Long" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > 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.)


 
Reply With Quote
 
Lazarus Long
Guest
Posts: n/a
 
      08-09-2004
On Mon, 9 Aug 2004 11:41:26 -0400, "skymuffins"
<(E-Mail Removed)> wrote:

>
>"Marvin Margoshes" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>>
>> "Lazarus Long" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed)...
>> > 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.

 
Reply With Quote
 
David Littlewood
Guest
Posts: n/a
 
      08-09-2004
In article <(E-Mail Removed)>, Lazarus Long
<(E-Mail Removed)> 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
 
Reply With Quote
 
David J Taylor
Guest
Posts: n/a
 
      08-09-2004
David Littlewood wrote:
[]
> 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


For much action phtotography, the secret is to half press the shutter to
lock focus and exposure - keep your finger on the button and press at the
critical moment. Zoom up to 420 mm at f/2.8 with image stabilisation is
available in cameras such as the FZ10:

http://www.steves-digicams.com/2003_...z10.html#specs

at a considerable saving on the price of the DSLR equivalent. So you pays
your money and takes your choice.....

Cheers,
David


 
Reply With Quote
 
Dave Martindale
Guest
Posts: n/a
 
      08-09-2004
Lazarus Long <(E-Mail Removed)> writes:

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


Infinite focus means just that. If you set the camera to infinity, then
the objects in best focus is something so far away that the rays of
light reaching the camera are parallel - a distant landscape for
example.

Closer objects will be less sharp, though *how much* less sharp depends
on focal length and aperture. This is where "depth of field"
computations come into play.

>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.


No, it probably picked some random value that seemed best to it (without
a real target to focus on). With my cameras, at least (Canon), they
light a LED and draw a different-coloured box on the LCD to tell you
that they failed to focus, though you can force the camera to take a
picture anyway in that state.

>So if I had manually set
>infinite focus, how close to the camera would something appear to be
>in focus?


Do a web search for "depth of field" for the answer to that question.
But with the very short focal length lenses on most digicams, probably
anything that was still in the air would be far enough away for good
focus.

For this type of photography, switching to manual focus and setting
infinity is the right approach.

Dave
 
Reply With Quote
 
Ron Hunter
Guest
Posts: n/a
 
      08-09-2004
Lazarus Long wrote:

> 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?


For practical purposes, anything over 50 away from an ordinary sized
lens will be 'infinite' focus.
 
Reply With Quote
 
Joseph Meehan
Guest
Posts: n/a
 
      08-09-2004
Lazarus Long wrote:
> 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?


David L has the most complete and totally accurate answer to your
question.

I will try to have the shortest accurate answer:

Infinity is infinity, but it is safe to say that any aircraft flying
that you are photographing at an air show will be as sharp as they can get
with the camera focused on infinity. You best bet is to lock the focus on
infinity.

Motion (yours and the aircraft's) is a common cause of less than ideally
sharp images at such events.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math



 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Re: How include a large array? Edward A. Falk C Programming 1 04-04-2013 08:07 PM
How to close a TCP socket? (TCPSocket#close doesn't close it) IƱaki Baz Castillo Ruby 7 01-12-2010 01:32 PM
Why does JdbcRowSetImpl.close() close the database connection? Paul van Rossem Java 0 04-07-2005 07:01 PM
JavaMail POP3 folder.close() method close also store! Daniel Albisser Java 1 04-07-2004 03:45 PM
How to close child browser while parent close? Denon ASP .Net 1 11-14-2003 08:14 AM



Advertisments