Depth of Field/Exposure time Question

Discussion in 'Photography Beginners' Forum' started by Jubei, Sep 22, 2008.

  1. Jubei

    Jubei TPF Noob!

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    Hello, new to the forum.

    Would like to ask a question regarding depth of field and exposure time.

    I use a canon DSLR with a 50mm 1.8 aperture lens.

    When I take a photo and the background is a bit further away it becomes VERY blurred. I DO want the depth of field effect but I dont want the background to become SO blurry that it's completely indistinguishable. What can I do about that? If I decrease the aperture from 1.8 to say 4 then automaticaly the exposure time increases and the subject becomes slightly overexposed.

    Is there anything I can do to avoid that?

    a very good example of the effect I am trying to achieve is this photo:
    http://www.fightingmaster.com/legends/kanazawa/kanazawa.jpg

    if I were to take it with my 1.8 lens the background would be incredibly blurry and you wouldnt be able to see anything.

    Nick
     
  2. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Hmm which mode are you shooting in?
    Reducing the aperture from f1.8 to f4 (a larger f number means a smaller aperture - less light entereing the camera - so its called reducing) will increase your depth of field - so less blur - hence the need for a slower shutter speed (longer exposure time).
    If you are getting blowouts then try shifting to full manual mode and using the cameras built in meter underexpose the shot - that should help prevent overexposed blowouts -- or use exposure compensation in aperture or shutter priority modes - a negative value down to -1 at most should be enough
     
  3. Dao

    Dao No longer a newbie, moving up!

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    You may want to experience more.

    There are few factors that cause the blurred background.

    1. The distance between the camera and the main subject.
    2. The distance between the main subject and the background.
    3. The Aperture size.
    4. The sensor size. Of course, you cannot change your camera sensor size. (unless you use the same setting with the same lens on a different camera body)

    In your case, I believe you can try changing the value in point number 1 and 3. Like increase the distance between the main subject and the camera and increase the Aperture F number (decrease the actual Aperture size).

    I will try it in Aperture Priority (Av) mode.
     
  4. Village Idiot

    Village Idiot No longer a newbie, moving up!

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    Don't close the aperture so much. f/2.8 should still give you a shallow DoF
     
  5. Jubei

    Jubei TPF Noob!

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    I was shooting in the P mode where the camera automaticaly adjusts exposure time.

    Thanks for the tips guys. I guess I will try it in manual mode with the exposure compensation.
     
  6. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    in full manual mode exposure compensation is not active - you have to watch the meter and set the shutter speed, aperture and ISO to get the meter to show slight underexposure -- exposure compensatin is for the more auto modes - like aperture priority and shutter priority - where the camera controls one of the variables for you -- I think it migh also work in P mode though I am not sure
     
  7. srt86hil

    srt86hil TPF Noob!

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    As far as I'm aware, you can't control the f-stop in P mode, only the overall exposure - to have more control over the DOF you'll need either Av or M mode.
     

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