# Calculating aperture vs DOF (re infinity)

Discussion in 'Photography' started by BD, Dec 12, 2005.

1. ### BDGuest

Hi, all.

Is there a quick and dirty way I can calculate ahead of time the
'minimum' distance that will be in focus when I set my camera to
infinity, given a specific f-stop?

reason I ask is I want to take pictures of a _large_ area, in low
light, and want to keep as much in focus as I can. But I also would
like to minimize my exposure because people may be milling about during
the exposure - it's a public area.

If not for the possibility of passersby, I'd go for f/16 or higher,
thereby ensuring that most of the area is in focus. But to also capture
the moving people, I'd want to go wide open. My 50mm lens goes to
f/1.8, and I am getting a 150mm f/2.8 next week.

If I knew that (for example) at f/1.8, with focus set at infinity (or
the far end of the subject area), everything up to 500 feet would still
be in focus, I could more easily gauge what the best balance of
aperture and exposure will be for my efforts.

Hope I'm making sense.

Thanks,

BD

BD, Dec 12, 2005

2. ### UCGuest

UC, Dec 12, 2005

3. ### BDGuest

It's called the hyperfocal distance.

Ah, very good! Thanks!

BD, Dec 12, 2005
4. ### BDGuest

It's called the hyperfocal distance.

What it says to me is that if you have your camera set to infinity,
then going by the chart in the article, an object will be in focus up
to the distance indicated.

So, if you then focus on an object that same distance away (or an
object between that distance and infinity), then objects at infinity
will still remain in focus, as will objects that are closer than that
distance. You're making better use of your focal range.

The analogy I see is one of a sphere: your focal range is a sphere, and
when you focus on an object at the very back of the scene, you're
'wasting' half of your focal range, because half of it is behind the
object at the back of the scene. So focusing on an object closer than
the very back will bring more objects into the focal range, and still
keep the objects at the far back in range as well.

Does that analysis make sense? Do you agree? Am I completely confused?

BD, Dec 12, 2005
5. ### UCGuest

Correct.

UC, Dec 12, 2005
6. ### BDGuest

Correct.

Very useful.

BD, Dec 12, 2005
7. ### Mark W. OotsGuest

Many lenses have the f stops printed on both sides of the focus mark. If you
set the f stop to f16, then set the inifnity mark to the f 16 mark on that
side of the focus mark, then everything between the f 16 marks are in focus.
And yes, it is called the hyperfocal range or hyperfocus. Many of the large
format senics that you see use the same method, but perhaps with apetures as
small as f 64, with everything from a foot or 2 to infinity in focus.

It can be very valuable when doing "grab shots" while walking along. Set to
the hyperfocal, point, shoot. Also handy for shooting over crowds, "the Hail
Mary" shot, hold camera high, point, shoot, pray!

Zoom lenses are harder to preset, since you get greater DOF at shorter focal
lengths.

Mark

Mark W. Oots, Dec 13, 2005
8. ### BDGuest

Many lenses have the f stops printed on both sides of the focus mark.

I don't believe I'll have that available; this is for a DSLR, and I
don't recall seeing any printed f-stop markers on the lens.

BD, Dec 13, 2005
9. ### PcBGuest

Many lenses have the f stops printed on both sides of the focus mark.
You can get depth-of-field calculators on the web, see

http://dfleming.ameranet.com/custom.html
http://www.outsight.com/hyperfocal.html
http://bobatkins.com/photography/technical/dofcalc.html

etc.

Perhaps you could compile a series of tables to carry with you?

--
Paul ============}
o o

// Live fast, die old //

PcB, Dec 14, 2005
10. ### BDGuest

Perhaps you could compile a series of tables to carry with you?

That's exactly what I plan to do; I have seen some of these calculators
(thanks for that), and will insert some likely focal length and
aperture values to get the hyperfocal distance etc. Should prove useful.

BD, Dec 14, 2005
11. ### T RockGuest

Is there a quick and dirty way I can calculate ahead of time the
It's also useful to decide what to focus on and then calculate what else is
in focus...

The code I posted in the 'DOF Calculator' subject below runs in a
keystroke-programmable RPN HP calculator. Once the code is keyed into the
calculator it stays in the calculator until the batteries die. Of course the
idea is that a computer is not going to be carried with the camera equipment
but a LCD calculator can be carried...

Put the COF (in meters) that is relevant to your camera on line A15 in the
code...

T Rock, Dec 14, 2005