DOF Question

Discussion in 'Photography Beginners' Forum' started by jwhphoto, Sep 21, 2008.

  1. jwhphoto

    jwhphoto TPF Noob!

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    What settings are generally used to create DOF? is it a larger aperture? I really am not sure how this works and would like some more information so i can try this out. Currently i only have a 18-135 mm lens, so is this lens able to do good DOF?

    Thanks

    jwhphoto
     
  2. Early

    Early TPF Noob!

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    As you close down the lens, the more DOF you will get. Also, wide angle lenses will give you more DOF then telephotos.
     
  3. kundalini

    kundalini Been spending a lot of time on here!

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    Each lens at each aperture setting has DOF. Wiki definition.

    What are you trying to accomplish?
     
  4. jwhphoto

    jwhphoto TPF Noob!

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    Heres a pic i took today in downtown Sacramento. It was taken at 18mm, f/4.0, 1/200 sec. I was able to blur the background some, but i would like less detail than this in some of the other ones i shoot. (getting the blur in this pic was luck for me, i still dont know how to do it exactly) What i want to do most is if i take a close up of a flower, and there are other flowers 2-3 feet behind it, i want those quite out of focus.

    Also feel free to C&C this photo please.


    [​IMG]
     
  5. Josh66

    Josh66 Been spending a lot of time on here!

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    For that you'll need a large aperture (small f/#). The larger the aperture, the more out of focus the background will be.
     
  6. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Well the wider the aperture you use (the smaller the f number) the smaller your depth of field gets (the area in a shot which is in focus). Once you are at the widest your lens will go then the only other way to increase the blur is by distance - from you to subjcet and from subject to background.
    In the case of the shot you show above you have done the right method - the subject (in focus) is close to the lens - whilst the background if much further off. Couple that with a wide aperture to get your background blur.

    I think to get more blur - unless you add blur in editing - then you need a wider lens - f2.8/1.8 area
     
  7. kundalini

    kundalini Been spending a lot of time on here!

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    If that 18-135mm lens is the Nikon version, then f/3.5 is your maximum aperture. You are likely to get better image quality at f/4 to f/5.6 than at f/3.5, however you'll need to check reviews at photozone.de or somewhere for actual results.

    Another factor to achieving the blurred effect (bokeh) you're after is focal length in addition to what Overread stated with regard to subject-to-background. I'm fairly confident that the wider the field of view, the less bokeh effect you will get.

    Try this at you leisure, set up an inanimate subject, anything... a can of soup, set of bongos, your ex-girlfriend.... Have the background a minimum of at least 5 feet from the subject. With camera-to-subject and subject-to-background remaining constant, take test shots at varying, but precise, focal lengths.... say 18mm, 50mm, 85mm, 100mm, 135mm. All at the same aperture. So if your maximum aperture at 135mm is f/5.6, set all shots at f/5.6. This should give you an idea of what part focal length plays with the blurred background. Of course the next excercise will be to keep the maximum aperture at those same focal lengths and that will tell you what your lens is capable of.

    Just a thought. Someone else will come along and have a better idea. :biggrin:
     
  8. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    hmm you reminded me Kundalini - out of interest when you say wide field of view do you mean a shorter focal length?

    I think its the greater the focal lengths that lead to increased background blur
     
  9. Resin42

    Resin42 TPF Noob!

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    Is this the world's tallest Dalek? :D
     
  10. kundalini

    kundalini Been spending a lot of time on here!

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    Maybe I screwed the terminology up, but 18mm is a wider field of view than 135mm.

    Also when going more towards the telephoto end of focal lengths, you also get compression which aids in achieving bokeh with a wide aperture and isolating subject from background, provided there is a distance of subject-to-background.

    Correct me if I'm wrong, please.
     
  11. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    ahh no you were right = it was late and I read your point backwards!
     
  12. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    Not sure if this was said, but the closer to your subject you are the more shallow your depth of field. (less in focus)

    This is in addition to the effect of aperature.

    This also works in reverse, so the further away you are the more that is in focus. This is handy because it allows you to use very wide aperatures when shooting landscapes, which tends to give you sharper images up to the point closest to you where the focus will fall off. (which can be adjusted by hyperfocal focusing)

    Some valuable links:

    http://www.thephotoforum.com/forum/showthread.php?t=130556
    http://www.great-landscape-photography.com/hyperfocal.html
    http://www.dofmaster.com/hyperfocal.html
     

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