Front tilt focus concern

Discussion in 'Exposure Discussion' started by shyguy, May 15, 2005.

  1. shyguy

    shyguy Member

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    I believe I am seeing something I haven’t found reference to in my books. When employing front tilt to bring the near and far objects into focus, I believe I am seeing the center area go out of focus. The final image on the negative and print will sometimes show what appear to be a sharp front object, and a sharp far object, with a middle ground that seems soft.

    Can anyone help explain what might be going on?

    S.
     
  2. noseoil

    noseoil Member

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    This one is covered in Jack Dykinga's book on Nature Photography, if you can find a copy, and shows examples of what you are asking.

    Basically, you are changing the plane of sharp focus to allow the near-far relationship to come into focus with the lens. The same type of relationship can be accomplished with rear tilt to accentuate the foreground, where you want to have near objects loom and look "larger than life." What is happening is the small amount of tilt (you did use a very "small" amount of tilt, didn't you?) employed to change the plane of sharp focus must be made up for by stopping down. In the same way dof is used by hyper focal distance and f stop, the middle ground is brought into sharp focus by stopping down once the near-far objects are brought into focus.

    A polaroid back will help give instant feedback to see this one. Once the near-far objects are brought into focus, the f stop is used to bring in the middle. Takes a bit of practice, but there are books which cover this subject (Steve Simmonds, Leslie Strobel, etc). tim
     
  3. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Yup. The situation where this happens is usually where you have some tall thing, like a mountain ridge in the distance, and you want the horizon in focus as well as something in the near field. Sometimes it makes sense to tilt and stop down, and other times just to stop down without using any tilt. If you're going to tilt and stop down, then sometimes it works to have the plane of focus go through a line somewhat lower than the horizon--like 2/3 the way up the mountain. If you've also got tall things perpendicular to the ground in the near field like tall trees or tall buildings, then tilt and swing usually won't help.
     
  4. rbarker

    rbarker Member

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    When using tilts, you may find it helpful to think of DOF as a wedge, with the narrow end nearest the camera. The plane of sharp focus is essentially in the center of the wedge. Due to the wedge shape, it's very easy for other near and middle-ground elements in the scene to extend above or below the wedge of DOF, even at fairly small apertures.

    As others have said, the choice is then to find a more optimal placement for the plane of sharp focus, not use tilt and rely on just aperture for the required DOF, or choose a different composition that works better.
     
  5. shyguy

    shyguy Member

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    so it's all about the plane? items within the plane, front to rear will be in focus. items outside of the plane will not be in focus.??
     
  6. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Yes.
     
  7. photobackpacker

    photobackpacker Advertiser Advertiser

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    I got a very helpful hint at a seminar - When checking near/far focus and adjusting tilt - You normally extend for near focus and retract for far focus. When this relationship reverses - you have added too much tilt.
     
  8. shyguy

    shyguy Member

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    yes, i have seen that. I have been trying to use tilt as a way to get the DOF i need while keeping the aperture open more than usual to gain speed.

    Stroebel goes into this a bit, but not the out of focus side affects. I re-read Dykinga and i see he touches on it a bit.

    I appreciate all your input. I'll pay more attention to the plane itself. Perhaps lowering my far point of focus a bit to broaden the in focus field applied by the now reduced aperture .

    S.
     
  9. Ole

    Ole Moderator Staff Member Moderator

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    I suggerst you read Harold Merklinger's "The INs and OUTs of Focus", which can be found here togerther with a LOT of other useful information.
     
  10. shyguy

    shyguy Member

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    Thank You Ole. I'll give it a look.

    S.

    Ps. Wow that's quite a site. Lots of info. Thanks
     
  11. rbarker

    rbarker Member

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    Yep. That's why the short guy on the "Fantasy Island" TV show kept exclaiming, "The Plane, The Plane!" :wink: