Setting focus by distance settings

Discussion in 'Canon EOS' started by mary_beth_aiello, Mar 31, 2008.

  1. I just returned from shooting sunrises/sunsets at Hilton Head, and am generally
    not pleased with the lack of depth of field with many of the photos. I'm now
    reviewing back to basics.

    In one photography book, Understanding Exposure, by Bryan Peterson, he suggests
    presetting focus by using the distance setting on the lens. In theory, I
    understand what he's saying, but in practice I'm confused as to how you line up
    the numbers. IF you want depth of field to infinity, you line it up with
    infinity? But if you want five feet, you line it up to five feet? I don't think
    that's what he's suggesting. Also, where do you focus initially? Foreground?

    You can see my confusion! Please help. Your comments are more than welcome.
  2. This is not very practical with modern AF lenses because the focus ring arc is too short. Also many lenses do not have any DOF scale. You can try and work with tables or use a different method all together, I tend to use the new method. See
  3. The apeture of the lens controls the depth of field, the distance markings on the lens represent the distance to the in-focus, for lack of a better term. To increase depth of field, stop the lens down to something like f/11. Another way to do it is, depending on what make/model camera you have, use the DOF mode. At least with my Canon EOS-30, you put the center focus point on one extreme of the the range you want in focus and then do the other extreme, then take the picture, the camera will set the apeture so that, if possible, the range you selected will all be in focus. The distance markings, like Lester said, are essentially not very practical to use because there isn't really a fine adjustment. However, with manual focus lens, they have a silky smooth focus ring and have a wide range of rotation so you can be very precise.
  4. A couple corrections, the distance markings on the lens represent the distance to the in-focus POINT, and with my old film camera, in DOF mode, you push the shutter button after you put the focus point of one extreme of your desired DOF.
  5. This is what I usually do:

    1. Focus 1/3 into the frame.

    2. Use your DOF preview button to see if everything is focus.

    3. If the closest object still blur step back.

  6. I suspect that what your book was referring to was the use of something called hyperfocal distance. Google that and you will find explanations.

    As suggested this is difficult without the markings on AF lenses nowadays. Just use the aperture-preferred setting (Av) and set the aperture as small as you can and still have a hand-holdable shutter speed. (The old rule of thumb was that the slowest speed you could hand hold a lens at was the reciprocal of the focal length, thus a 135mm lens at whatever is closest to 1/135 sec on your camera). Of course, IS changes that.
  7. I'm with Lester on technique for shooting landscapes. Merklinger's approach makes good sense - i.e. maximise sharpness of the distant elements of the scene and make the foreground "acceptably" sharp. When maximising apparent sharpness with a crop sensor camera, you should allow for the fact that diffraction becomes noticeable a stop sooner than with a full frame one. Shoot at f/11. If you haven't got a tripod or if there is a blustery wind that means you need a high shutter speed to freeze motion in branches etc. don't be afraid to increase your ISO. You can use any high contrast edge in the distance to give AF something to work with, and at large distances focus/recompose error doesn't arise.

    Depth of field calculations (implicit in setting a focus distance manually from the focus scale) work best for mid distance subjects such as group portraits, where you need the front and back row to be equally and acceptably sharp.
  8. You would need a lens with a depth of field scale, or a pre-printed depth of field chart. You also need a lens with a distance scale; for instance, 50mm 1.8 is out.

    You set the infinity mark to the aperture on the depth of field scale that is to the right of the line with a Leica/Canon-style lens. To the left of the line with a Nikon, which focuses the opposite direction.

    Technically, if you have the freedom to do it, focusing on infinity will probably make a sharper picture.

    Of course, this is also difficult with a modern AF lens, because the focusing collar most often turns past infinity.

    I wish there was a button on your camera that would automatically focus it to infinity.

    It's much easier with an older camera.

    For now, I would just focus on a distance object, and make yourself a depth of field table for every aperture for when the lens is set at infinity, so you know ow far to stop down to get the closer objects sharp.

  9. Mary Beth, much seems missing in your description of what you were shooting and what your intent was. that makes it difficult to address your particular issue. That having been said I will go out on a limb here and venture a guess that you were shooting landscapes at sunrise and sunset intended to capture the sun as a primary element of the image. If it was your intent in this low light situation to have enough depth of field to include objects relativly near the camera in focus, you should have been using a rather small aperture, (big f number). To do this in low light, you probably need a tripod or other mechanical means of holding the camera steady for long exposures no matter what ISO and lens you used.

    There is no information in your post about whether or not you used a camera with a depth of field preview function although virtually any camera should be able to do this one way or another even if it means putting everything in manual mode and composing the image that way first before going back to one of the more automated aperture priority modes. This makes the short version of the answer "aperture priority and DOF preview".

    The secret about dof that some folk struggle with is that the point of focus is not at the center of the dof zone. If you focus on a point ten feet away and chose an f stop that should provide a dof of six feet, your field of focus will not extend from seven feet to thirteen feet. The real answer is more like eight feet to fourteen feet. focus is more critical the closer you get to the primary optic.

    Hence the answer becomes aperture priority and dof preview. If it is too dark to be certain, compse the image with the aperture wide open so you have enough light to see all of the elements, stop down all the way and manualy focus fifteen feet away.

    That should focus everything sharply. If your intent is to have some things out of focus... well that's different. And if you are using a film camera be mindefull of recipricosity failure.
  10. From this site, download the DOFMaster Hyperfocal Chart:

    Then install it on your computer (it will put a neat little icon on your screen).

    When you run it, it will produce a chart; I have one for each of my lenses printed on light cardboard in shirt pocket size.

    The options are as follows:

    1. Chart size (any size you want),

    2. Title, the default is Hyperfocal Distance Chart, but your lens info can be entered,

    3. Short lens length/long lens length - useful for zooms,

    4. Distance units (feet or meters),

    5. Minimum and Maximum Distances

    6. Minimum and maximum f/stops of the lens (or the ones you use),

    7. Show 1/2 or 1/3 stops,

    8. Circle of Confusion. Elsewhere on the site, they list the values for various cameras.

    Print your chart(s).

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