Calculating aperture vs DOF (re infinity)

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

  1. BD

    BD Guest

    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
    #1
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  2. BD

    UC Guest

    UC, Dec 12, 2005
    #2
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  3. BD

    BD Guest

    It's called the hyperfocal distance.

    Ah, very good! Thanks! ;)
     
    BD, Dec 12, 2005
    #3
  4. BD

    BD Guest

    It's called the hyperfocal distance.

    That was an interesting read.

    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
    #4
  5. BD

    UC Guest

    Correct.
     
    UC, Dec 12, 2005
    #5
  6. BD

    BD Guest

    Correct.

    Very useful. ;)
     
    BD, Dec 12, 2005
    #6
  7. BD

    Mark W. Oots Guest

    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
    #7
  8. BD

    BD Guest

    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
    #8
  9. BD

    PcB Guest

    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 //
    Gallery at http://homepage.ntlworld.com/pcbradley/NewGallery2.htm
     
    PcB, Dec 14, 2005
    #9
  10. BD

    BD Guest

    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
    #10
  11. BD

    T Rock Guest

    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
    #11
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