Question from 'Understanding Exposure' by Peterson

Discussion in 'Photography Beginners' Forum' started by smackitsakic, Apr 6, 2010.

  1. smackitsakic

    smackitsakic TPF Noob!

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    Hi folks!

    This weekend I picked up the book 'Understanding Exposure' by Donald Peterson at the suggestion of some of the posters on here.

    So far, GREAT book!

    As I was reading it last night I was on the section about storytelling apertures. I think it's around page 35. It speaks to using an exposure where everything is sharply in focus by pre-setting your depth of field.

    I read this about 5 times and can't seem to grasp the concept of what Peterson is trying to tell the readers. Can anybody please try to explain to me what Peterson is trying to explain to me? How is it possible to pre-set the depth of field to get sharply focused images?

    Also, my camera is a Canon and has a depth of field preview button...how does this relate to pre-selecting a depth of field?

    Any help to this new photographer would be great!

    Thanks.
     
  2. Goontz

    Goontz TPF Noob!

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    I don't have the book handy, but it sounds to me like he's probably just talking about using a certain aperture to get the depth of field that you want for your shot, then adjusting the shutter speed accordingly for the correct exposure (or maybe just using Aperture Priority mode).

    Remember: Aperture size will directly affect your depth of field. Thus, choosing the appropriate aperture would be pre-setting your [desired] depth of field. This would be opposed to if, for example, you were shooting sports and you knew that a fast shutter speed is most important to freeze the action, and didn't care as much about your aperture or depth of field.

    If you want a shallow depth of field for what you're trying to achieve, you'd use a large aperture (think f/1.8 - maybe f/3.5 or f/5.6 in the case of your kit lens). If you're shooting a landscape (which sounds like the case for a "storytelling" aperture) with everything in focus, you'd choose something more like f/13 or smaller. He'll refer to f/8-f/10 as the "I don't care" apertures because they're a middle ground for when a specific depth of field isn't desired. With these, the DOF wouldn't be as nearly as shallow as when wide-open, but would also not be as deep as with an even smaller aperture.

    As for the DOF Preview button: Your camera has the aperture as large as it will go anytime you're simply looking through the viewfinder. This is so that it can let as much light in as possible so you can see through it. Right before it actually takes the exposure, it stops the lens down to whatever aperture you'll actually be shooting at. Pressing the DOF Preview button simply makes it stop the lens down to whatever aperture you're set at so that you can get an idea of how deep your DOF will be. Set your aperture to something small (f/10 or smaller). Look through the viewfinder at something and push this button. You'll notice that even things in the background will be more in-focus than they were before. It will also appear darker because the aperture is now stopped-down and not letting as much light through for you to see.
     
    Last edited: Apr 6, 2010
  3. Dominantly

    Dominantly TPF Noob!

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    I believe it is Bryan Peterson that you are referring to.

    Story telling apertures are basically shot at f/22, with the focal point set about 5ft from your lens (18mm is a good place to start with your focal length).

    The idea of the "Story" is to have something interesting throughout the whole picture. For example, a nice set of rolling hills with flowers or tall green grass, then a nice old oak tree standing along in this field as your middle ground, then maybe a nice snow capped mountain range in the background.
     
  4. smackitsakic

    smackitsakic TPF Noob!

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    Thanks for the comments.

    DOMINANTLY, what do you mean by having the focal point 5 feet in front of your lens? That is the part that I don't get.

    In one of Peterson's examples he talks about setting the focal point to be 2 feet in front of the lens, set the depth of field, then move the camera to take the picture. This is the part that confused me, and still kind of is confusing to me.

    I have a fairly good understanding of DOF and that a higher f-stop will result in a shallower DOF. It seems like Peterson is trying to tell readers that there is something more to it than this, but maybe i'm just reading it wrong.

    I'll try to play around with the DOF Preview button on my Rebel. He mentions on a side note something about Canon cameras beeping if the DOF isn't appropriate, or something like that. It's written in a confusing way in my opinion. Am still a bit confused!
     
  5. Goontz

    Goontz TPF Noob!

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    Focal point is basically just the main point of interest in the shot; the object that you're focusing on. With a large aperture, it may be the only thing in focus, while with a very small aperture, everything would be in focus.
     
  6. Vinny

    Vinny TPF Noob!

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    I've never read the book but by pre selecting an aperture and pre focusing the lens you are taking shots with all the same depth of field/focus. The aperture is the mechanism that gives you the depth of field. A f 1.4 has a much narrower DOF than a f 11 than a f 22. Some people prefer aperture priority so they can control the DOF.

    Personally I always had a hard time seeing the DOF in my camera (maybe that's something I need to work on!) but with digital it should be a simple matter of pointing and clicking.

    As far as a camera knowing what depth of field is correct ... how does it know what effect you're looking for? I would ignore that section or turn that off in the camera.
     
  7. Goontz

    Goontz TPF Noob!

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    :scratch:
     
  8. Vinny

    Vinny TPF Noob!

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    What don't you understand Goontz?

    I was explainig why you might set aperture and pre focus - did I explain something wrong?

    The fact that I could never see depth of field through my camera is something I never worked on. I usually knew what look I was going for and took the picture with different apertures around what I wanted.

    Camera not agreeing to the depth of field - you are in control of your photos.

    Please explain.
     
  9. Dominantly

    Dominantly TPF Noob!

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    What that means is you can point your camera to something 5ft in front of you, lock focus on it, then recompose and shoot.
    I do not like to lock and recompose, so I would just move a focal point using the thumb pad, down to that point 5ft in front of me and do it that way.
    This is suppose to ensure you have clarity throughout the whole scene, vice focusing on something further away and having a soft foreground.
     
  10. pbelarge

    pbelarge TPF Noob!

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    I, like the OP am confused about how all this focusing and refocusing actually works. I think this thread has some good info and a couple of intelligent people here.

    Could one or both of you try to explain it to us a little differently, maybe more detail? or maybe send a link that has this information available in a format that I (very inexperienced) can understand.

    Thanks in advance of your response!!!
     
  11. smackitsakic

    smackitsakic TPF Noob!

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    This is the part that still confuses me:

    What that means is you can point your camera to something 5ft in front of you, lock focus on it, then recompose and shoot.

    I now understand what it means to have a focal point, but how do you lock focus on it? And what do you mean by recompose? That's the part that i'm not comprehending:)

    Thanks for the patience with us newbies! Glad there are some photographers willing to share their vast knowledge!
     
  12. Dominantly

    Dominantly TPF Noob!

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    So imagine that your camera has a cone shaped field of view attached to the lens cap (and it's rigid). If you aim the camera higher, the bottom of that cone points to a ground point further away. If you point it at a sharper angle down towards the ground, you gain more detail area closer to you, but loose some way off in the distance.
    The bottom of that "cone" area where it is seeing the ground in front of you is your Hyper Focal Distance.
    What does this mean? Well, the sharp portion of your photograph at an aperture of f/22 and a hyperfocal distance of 10ft, would be 5' to infinity. The closet point of clarity/sharpness is 1/2 of your focal distance. So if you were going for that lanscape shot, but focused on a set of trees 150ft in front of you, you would have robbed yourself of the maximum clarity and sharpness in the first large portion of your photograph.

    Here is another example.

    You have a Nikon D60, with the 18-55mm lens, your subject is 10,000ft away from you, and you want everything in the frame as sharp as possible.
    Your Hyperfocal distance would be 2.41ft, AND your depth of field would extend from 1.205ft to infinity (1/2 of your Hyperfocal distance).


    Check this website out
    Online Depth of Field Calculator
     

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