How to determine infinity focus distance?

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How can I determine at what distance the Canon 300D kit 18-55 lense (or any
lens for that matter) starts to focus at infinity.
I am setting up a table of hyperfocal distances and I want to ignore
distances beyond which the lens will be focusing at infinity.
Is it 63 metres or 200metres or 1 kilometre??? Is there an equation that
will calculate this?
regards
PeterH

Archived from groups: rec.photo.digital (More info?)

"My View" <reply to newsproup@NOSPAM.net> writes:
>How can I determine at what distance the Canon 300D kit 18-55 lense (or any
>lens for that matter) starts to focus at infinity.
>I am setting up a table of hyperfocal distances and I want to ignore
>distances beyond which the lens will be focusing at infinity.

First, you should understand that there's a contradiction in your
question. The lens "focuses at infinity" (meaning it gives the sharpest
image of things a long way away" only when it is actually set to the
infinity position, not somewhere nearer.

Now consider depth of field. Given a particular criterion of
acceptable sharpness, usually expressed in terms of the size of the
"circle of confusion", the depth of field is defined to be the range of
subject distances that are acceptably sharp. This doesn't mean that
the whole range of depth is equally sharp; it's not. And the near and
far limits of the depth of field are, by definition, right at the
minimum limit of acceptable sharpness.

The hyperfocal distance is the lens focus distance that makes the far
limit of depth of field equal to infinity. In other words, everything
from some near limit all the way out to infinity is acceptably sharp,
and this is the setting that maximizes the range of depth that is so.
Thus, it's useful when you absolutely need this. But it guarantees that
objects at infinity are just acceptably sharp, not good and sharp. You
*will* get sharper images of distant objects if you set the lens closer
to the infinity mark than at the hyperfocal distance.

>Is it 63 metres or 200metres or 1 kilometre??? Is there an equation that
>will calculate this?

Having said all that, there is a formula that will calculate hyperfocal
distance, which should be found in any good lens or photography
reference book. But it depends on focal length *and* aperture *and*
your chosen circle of confusion size. You'd normally pick some fixed
value for CoC, then calculate a 2D table of hyperfocal distance as a
function of focal length and aperture setting.

Dave

Archived from groups: rec.photo.digital (More info?)

"Dave Martindale" <davem@cs.ubc.ca> wrote in message
news:cr5amo$c17$1@mughi.cs.ubc.ca...
SNIP
> Having said all that, there is a formula that will calculate
> hyperfocal distance, which should be found in any good
> lens or photography reference book.

Or on the web as a small Windows application at:
<http://www.bobatkins.com/photography/technical/depth_of_field_calc.html>,
which directly gives the "point blur diameter at infinity" as you move
the slider through the distance setting. That also allows to set the
CoC to one value and play with the other settings for the amount of
infinity defocus, while giving a warning if the aperture setting
causes the diffraction circle to exceed.

Bart