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Thread: Depth of field on tilted plane

  1. #1

    Depth of field on tilted plane

    All the depth of field calculations I have seen are assuming a lens parallel to the film plane. What happens when you tilt the lens putting the plane of sharp focus at an incline? Is there a simple method to calculate the depth of field at a given distance from the camera if the anlge of the plane of focus is knows?

  2. #2

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    Depth of field on tilted plane

    Yes Dave. There are several papers dealing with this issue. You can read this one in English. http://www.galerie-photo.com/profondeur-de-champ-scheimpflug-english.html. There is a pdf copy on Tuan Luong information web site. Basically for small tilts angles, a simple model can be derived and the corresponding DOF region in object space is contained between two slanted planes, a wedge-shaped volume. The more you stop your lens down, the more the wedge opens. The model fails at high tilt angles not used in practice in landscape LF photography.

  3. #3

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    Depth of field on tilted plane

    The Rodenstock Scheimpflug/DOF calculator computes both at angles of 0, 10°, 15°, 20°, 30°, 35° and 40°. The difference at infinity and on 4x5 between 0 and 40° tilt is 2/3rds stop. At 1:1 it is about 1 stop.

    The calculator also computes DOF at 1:1, 1:1.15, 1:2, 1:3, 1:4, 1:5, 1:10, 1:20 and at infinity. And for camera formats of 35mm, 6x4.5, 6x6, 6x7, 6x9, 9x12, 4x5, 5x7, 18x24 and 8x10.

    Every change in angle of the camera, film size and reproduction ratio will make some change in the DOF and in Scheimpflug settings. The Rodenstock calculator shows these settings and differences very plainly and simply.

  4. #4

    Depth of field on tilted plane

    Dave

    One answer is to determine not the DOF, but the aperture required for the DOF you need: there is a scale for this purpose on Sinar monorails.

  5. #5

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    Depth of field on tilted plane

    "there is a scale"

    Many cameras have a "scale. The one on the Linhof GTL computes aperture at 5 different magnification ratios, for instance, not just one.

  6. #6

    Depth of field on tilted plane

    Bob:

    Do most monorails have the "apeture for required DOF" scale, or which cameras do?

  7. #7

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    Depth of field on tilted plane

    Linhof does and so do some Horseman cameras. You would have to ask about others. Not all scales are the same and Linhof currently has different types for the M679 series and the GTL series.

  8. #8

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    Depth of field on tilted plane

    Maybe we use different kinds of "depth of field" tables but the one I use is made by Linhof and bases the necessary aperture on the distance the lens travels between focusing on the near and focusing on the far (the greater the distance the smaller the aperture). It's always been my understanding that when using this and similar tables you first apply whatever tilt or swing you're going to use and then just do the measuring. In other words, nothing special required to use these tables with front tilt.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  9. #9

    Depth of field on tilted plane

    I have a Sinar F2 as well as a field camera so I am familiar with the scales DOF tools on the Sinar. My question is how to determine the DOF for a subject that is 5 feet from the camera and at 50 feet from the camera when the plane of focus is inclined from beneath my feet to the top of the building. It came up last week when I was trying to capture an old pump in front of a barn out on the prairies. I realize the DOF is such that I may not get the full height of the pump which is several feet away and the barn at a distance in focus. I was hoping for a simple formula that I could run on my Palm Top. I use Bob Wheeler's Vade Mecum but can't understand a way to make that particular calculation. Maybe I just need to re-read Wheeler's notes again.

  10. #10

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    Depth of field on tilted plane

    Dave,

    With the Rodenstock Pocket Calculator you simply do the following:

    1: set the angle of the camera rail on the outer white scale. 2: set the blue scale to the format size 3: set the magnification ratio on the inner white scale. 4: measure the distance from the near to the far point on the monorail. If your camera does not have an accurate scale the calculator has an 8cm ruler on it. 5: read and set the aperture opposite the extension used in 4 above. 6: set the standard to 1/2 the difference between the near and far point found in 4 above.

    Note: a seperate scale indicates any exposure compenstaion necessary for the magnification ratio used. None in your example.

    The calculator is fast and accurate and convenient to use and carry.

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