Need help with DOF

Discussion in 'General Gallery' started by Synergy, Aug 8, 2003.

  1. Synergy

    Synergy TPF Noob!

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    I recently took some pictures of various rivers and the like in Wales, upon developing I found that a large number of them had problems with focusing and depth of view. I’d appreciate any feedback people can offer concerning the following pics so that I might learn and improve.

    My own thoughts are..

    The one with the bee and leaves and the one with the red flowers I think I set the f stop too low. My plan was to have the big leaf, the bee and the flowers in front in focus and then the leaves in the background out of focus and all of the red flowers in focus but not the fence. I need to find out if things appear focused in front and behind of the point I’ve focussed on or if things appear focused in front or behind the point I’ve focused on.

    The rock picture I’m wondering if I should of focused on the top of the water or on the riverbed. I guess if selected a lower f-stop it wouldn’t have mattered. Although I ran the risk of under exposing the shot if I lowered the f stop as I had to keep the shutter speed high-ish so as not to cause the water to blur from its movement and it was dark.

    Is there a rule that says under so and so conditions f stop needs to be set to this to obtain certain DOF ? I was hoping to use one the flower shots in the macro challenge but don’t feel too happy about how they came out! We live and learn though…



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    Many thanks for your help

    Synergy
     
  2. Taryn

    Taryn TPF Noob!

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    I have a Cannon AE-1 Program (20+ year old, manual SLR with auto light adjustment), and on the front of my camera is a little button I can push in toward the lens to give me a preview of the depth of field. Does your camera have anything like that?

    What kind of lens did you use for these? Is your camera auto-focus? If so, it may be having trouble working on close-ups. Try shutting it off if you can, and adjusting focus by hand.

    The first shot looks like it was focused on the leaf in the background, and not the flower in the foreground. I think you'll have a longer depth of field (stuff will be in focus in the background as well as the foreground) with your f-stop at 11 or 16. If you want the background to be blurred out, choose a lower f-stop (5.6 or so). Keep in mind you may have to adjust the shutter speed to compensate.

    -T
     
  3. oriecat

    oriecat work in progress

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    Hey Synergy! I am not sure I understood all your questions, but I just thought I would throw out some depth of field stuff, in case it helps. :) First off, does your camera lens have a depth of field guide on it? That can be very helpful, because it would say what distances would be in focus depending upon what f/stop you were at.

    I am taking this all from "Basic Techniques of Photography: An Ansel Adams Guide" by John P Schaefer.

    "The depth of field of a lens increases as you stop it down. Each time you double the f-stop (for instance, from f/4 to f/8 ), you double the depth of field."

    "The depth of field decreases markedly as the focal length of the lens increases. Wide angle lenses, therefore, are capable of producing images with a very large depth of field, while with telephoto lenses the depth of field is usually severely limited."

    Here's a table with the approximate depth of field for lenses focused at 5 feet at f/22

    <u>Focal Length of Lens</u> <u>Range of Sharp Focus</u>
    20mm 1.5 feet to infinity
    28mm 2.5 feet to infinity
    35mm 3 - 20 feet
    50mm 4 - 8 feet
    85mm 4.5 - 5.7 feet
    135mm 4.9 - 5.2 feet




    "In addition to being controlled by the focal length and aperture of the lens, the depth of field is also a function of the camera-to-subject distance: the closer the camera is to the subje t, the more limited is the depth of field. You can increase the depth of field in a scene by moving further away from the subject. Doubling the camera-to-subject distance quadruples the depth of field because depth of field is proportional to the square of the distance between the subject and the camera. Thus, if the depth of field is 4 feet at a subject-camera distance of 10 feet, it will be 16 feet (4x4=16) if you increase the camera-subject distance to 20 feet."

    Hope some of that helps!
     
  4. oriecat

    oriecat work in progress

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  5. trbo187

    trbo187 TPF Noob!

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  6. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    DOF is modified by format (film or sensor size), aperture (f/stop), focal length, and camera to subject distance.

    There are many good DOF calculators on the web if your lens doesn't have a DOF scale on the focusing ring (there's probably one in the instructions). Remember, if you are using a zoom lens DOF changes with focal length.

    I love the second pic!! Awsome!!! Check out a photographer named Huger Foote.
     
  7. ChristopherGrant

    ChristopherGrant TPF Noob!

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    Read 'oriecat's' comments&uml;. S/he explains all the basics of DOF. Visit some how-to-sites! It looks as if your problem lies in aperture and focal lengths but this is just a guess. Perhaps you can post all the details of these shots?
     

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