Depth of Field questions

Discussion in 'Photography Beginners' Forum' started by Mugen80, Aug 31, 2009.

  1. Mugen80

    Mugen80 TPF Noob!

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    Please bare with my totally noobish question. Im a bit frustrated with trying to figure out DOF with my camera and lens. Im shooting with a T1i using the 18-55mm lens that came with it.

    With this lens, what is the max distance that my subject can be from me in order to get my subject in focus and the background out of focus. I had a hell of time getting the background out of focus when my subject was more than say 10-15 feet away. Is this because of my lens? If not then what in the heck am I doing wrong because its driving me crazy! :(

    - Jerry
     
  2. Plato

    Plato TPF Noob!

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    Go here and memorize the figures for the camera/lens/distance/aperture(s) that you're most likely to use.

    By the way, you're using a lens with a relatively short focal length and fifteen feet is (for that lens) "distant." If you also had a small lens opening (large f-number), your DoF will extend pretty far beyond the subject.
     
  3. Derrel

    Derrel Mr. Rain Cloud

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    Welcome to the world of small-sensor, crop-body cameras and slow maximum aperture kit lenses. The reason you can NOT get the background well out of focus when the subject is 10 to 15 feet distant is because your camera's sensor is very small, and therefore it uses short foal length lenses. The longer the camera-to-subject distance, the greater the depth of field becomes. With short focal length lenses, there is a great deal of depth of field, and with small apertures like f/5.6 to f/11, there is a great deal of depth of field. As Plato states above, the distance you are shooting at is relatively "far" with a short lens on a small-sensor camera that has slowish max. apertures.

    The problem comes from 1) small capture format with 2) correspondingly short focal length lenses with 3) small maximum aperture size and 4) moderately long camera-to-subject range of 10 to 15 feet.

    The very issue you are discussing is one of my main arguments against DX-size sensors for use in "serious" people photography. To compensate, you need a wider lens aperture, which comes from a much more expensive lens,and you need a longer focal length than an 18-55mm kit lens delivers.

    To compensate, one thing you van try is to shoot with the lens at its widest aperture settings. Focus VERY carefully. Make sure the background is as distant, as far behind, the subject as you can get and use the longest focal length setting you have on your zoom lens. The "kit lens" does not allow the type of foreground/background separation many people are hoping to achieve with a "good camera". On the other hand, the small sensor,short focal length lens settings, and smallish lens apertures CAN deliver deep depth of field and lessen the need for absolutely critical focus. Sort of the proverbial double-edged sword.
     
  4. musicaleCA

    musicaleCA TPF Noob!

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    Memorize? You memorize that stuff, Plato? Gee, I just take a guess "er...somewhere in the area of f/4...Yeeeeaahhh...lesse if that works." :lol:
     
  5. DScience

    DScience No longer a newbie, moving up!

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    I would be careful with the fact's your throwing out there. You don't need BOTH a faster lens and longer focal length. You can get either or, which both will have a factor on the DOF.
     
  6. Plato

    Plato TPF Noob!

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    I submit that you're exaggerating the issue. You can get excellent selective focusing with DX sensors without spending much money. Consider that a 50mm f/1.8 is about a hundred dollars and an 85mm f/1.8 is $450. Even a 50mm f/1.4 is only $400. That's a whole lot better than spending $2000 for an FX body with no lens.

    Here are some snaps that illustrate my point. (Check the pics on all four pages, especially the horse.)
     
  7. Plato

    Plato TPF Noob!

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    Naah, I don't memorize but the OP is a beginner. It's kinda like learning to drive. When you first start out, you had better be certain about the speed limit. After you learn how to drive, you don't give a damn!
     
  8. Dao

    Dao No longer a newbie, moving up!

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    Agree. A cheaper fast 50mm or a not so fast telephoto should be able to achieve what OP want to do. Of course, subject to camera and subject to background distance play important role as well.
     
  9. fiveoboy01

    fiveoboy01 TPF Noob!

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    There are plenty of DX-compatible lenses which won't break the wallet, while still being capable of delivering a narrow enough DOF to really screw up your image... if you're not careful with your focus point and/or subject positioning.
     
  10. Derrel

    Derrel Mr. Rain Cloud

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    Actually, the degree of selective focus possible with DX is VERY limited indoors. I'm very experiecned in multiple formats, having shot with 4x5, 120 rollfilm in 6x6 and well as 645, 35mm full-frame, 35mm half-frame long roll, as well as Nikon APS-C and Canon APS-C and Full Frame.

    Anybody thinking that I am over-stating the facts care to discuss specifics? Unless you have actually owned and photographed with FF digital, I have very little respect for half-formed opinions. 20-somethings who have learned on DX and amateur snappers who have only shot DX format digital have opinions that are rather ill-informed, in my book. if you don' actually OWN FF and DX, then your arguments are all based on second-hand knowledge, not empirical, first-hand knowledge.

    Read my blog entry about what DX format shooting does for people photography, and then come back and discuss some of the issues with some actual facts and figures, okay? There's a while host of reasons that serious people photographers (wedding, portrait,editorial) favor full-frame cameras over DX bodies,and why almost NO serious people shooters use the 4/3 format cameras.

    Derrel's Photography Blog: How The DX Format Impacts People Photography
     
  11. Plato

    Plato TPF Noob!

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    Well, let's see. My first serious camera was a "Honeywell Pentax" Spotmatic, advertised as the "world's first automatic SLR" because you could compose the shot with the lens wide open and the camera would automatically stop down the lens to the selected aperture when you pressed the shutter button. Personally, sonny, considering your condescending choice of words you're full of it.
     
  12. fiveoboy01

    fiveoboy01 TPF Noob!

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    "Very limited" selective focus capability? 50/1.4 wide open on a DX format D60:

    [​IMG]

    Doesn't look too limited to me. But maybe my eyes are bad.
     

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