DOF

Discussion in 'Photography Beginners' Forum' started by Weaving Wax, Apr 23, 2007.

  1. Weaving Wax

    Weaving Wax TPF Noob!

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    Ok...I'm a little confused..

    DOF is the distance in front of and beyond the subject that appears to be in focus. I know that the apeture will effect the DOF. The smaller the apeture the larger the DOF?

    What is the difference between DOF and selective focusing? I get a little confused... Does focusing effect the DOF?
     
  2. DSLR noob

    DSLR noob TPF Noob!

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    The larger the aperture (not greater, think size, not value) the less DOF the smaller the aperture, the greature the depth of field. As the aperture number decreases, the blades are opening up larger. An aperture of 1.4 if isnanely large, and has very little DOF, an aperture of 16 is very small and has large DOF. Take your 50mm 1.8 and put it on your camera body. Set it to aperture priority, look at the LCD and dial the aperture to 1.8, then ,looking into your lens from the front of your camera, adjust the aperture while holding the DOF preview button, this will show you that the aperture blades are gradually closing in as the number increases.

    As for focusing, focusing is for getting an object to be as sharp as possible, I.E. in the very middle of your DOF. A lens at F/8 with your camera's AF system focused on the object, will yield that object in nearly razor sharp focus. It will, on a magnified scale, be the most focused out of anything in focus in your picture (will be the same for objects that are the same distance from the camera).
     
  3. Weaving Wax

    Weaving Wax TPF Noob!

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    Thanks! That makes total sense now!
     
  4. xfloggingkylex

    xfloggingkylex TPF Noob!

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    another thing that effects DOF is focal length and distance from subject, as I have been discovering with my latest toy.

    It's a little hard to see on such a small image, but if you look at the bottom of the stem you can see where the focus is, and there is also a little sliver in focus on the sides of the apple directly across from the in focus stem. This spot is very very small even at this aperture, but you can make out the detail of some of the dust and the spots on the apple. Very very shallow. This is with aperture f/8 at 300mm about 38 inches away from the apple.

    [​IMG]
     
  5. Layton

    Layton TPF Noob!

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    When you say 'selective focusing' do you mean the effect like the lensbabies achieve? if so, i would like to know the answer as well.
     
  6. fmw

    fmw No longer a newbie, moving up!

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    Almost. Actually, DOF extends beyond the plane of focus about twice as far as it does in front of it. Lens focal length and camera to subject distance also affect DOF, by the way. Aperture is just one of three elements to consider.
     
  7. Weaving Wax

    Weaving Wax TPF Noob!

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    No...

    I mean something like this: [​IMG]

    Notice that the greenery in the front is the only thing in focus. But so is the fence in front of it..some of the greenery in the front is out of focus...but I got DOF and selective focusing confused. I now know that there are 3 different things that effect DOF.

    When you say focal length do you mean like the mm on the lens (sorry don't know all the technical terms yet). Like my lens is a 50mm?
     
  8. Digital Matt

    Digital Matt alter ego: Analog Matt

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    There is no such thing as "selective focusing". Every time you take a photo, you select a focus point. The amount of acceptable "in focus" part of an image is a factor of depth of field. How to control it has been discussed already. Just don't confuse it with a topic that doesn't exist.

    Yes, a 50mm lens would have a focal length of 50mm.
     
  9. Weaving Wax

    Weaving Wax TPF Noob!

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    Thanks. Someone else on here (can't remember whom) used the term "selective focusing". So I thought it was a real term.
     
  10. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Selective focusing makes sense, if you think of a lens baby, or any other tilt/shift type lens or camera. When you alter the lens angle to the film plane, you change the plane of focus, but that is not the same as depth of field, and does not apply to normal cameras/lenses.
     
  11. Weaving Wax

    Weaving Wax TPF Noob!

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    So...

    How does DOF preview work? I did use it and I did see the blades gradually close as the aperture got smaller and smaller... And at some of the smaller apertures (f/16) or so...I saw more of my image come into focus.. Is this correct or am I missing something...

    Sorry for all the questions, but I think I'm starting to get it...
     
  12. Digital Matt

    Digital Matt alter ego: Analog Matt

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    When you focus and compose your image, the aperture is always open to the max of the lens, even if your settings indicate f/22. When you press the depth of field preview button, it stops the lens down to the aperture in your settings, and thus gives you a preview of the dof. Unfortunately it also lets less light in, which makes it hard to see what you are getting.
     

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