DOF Preview

Discussion in 'Beyond the Basics' started by Harpua, Feb 11, 2006.

  1. Harpua

    Harpua TPF Noob!

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    Can someone please explain how the DOF preview is supposed to work on my camera (D70s)?

    My basic understanding is that when I hit that button, it should show me what the depth of field will look like on the final picture. Whenever I use it though I either do not see a difference or it becomes to dark to see anything. Am I understanding this feature wrong? Am I doing something wrong? Please educate a novice who is struggling to learn as much as I can. TIA!
     
  2. fightheheathens

    fightheheathens TPF Noob!

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    when your camera meters, the aperature is wide open all the time. So if you have a lens with the widest f value of 1.7, even when you set it to 22 the aparature will be at 1.7. If say you are at F/22, several things will happen when you hit the shutter button. First, the aperature will close to f/22 while the reflex mirror slides up and out of the way. then the shutter opens then closes and then the aperature returns to wide open. If you look at the lens of your camera while you take a picture, you can see the aperature close while the picture is taken.
    When you use the DoF preview button, it manually closes the aperature. The reason its open all the way when metering is because that lets in as much light as possible for you to see. (your camera can calculate using a simple program how much light will be let in based on your shutter speed and aperature. It only need read actual light, not the light that will actually hit the film plane. Making a smaller aperature means you let in less light to the camera and therefore it will appear dimmer to you. So thats why often the image gets very dim.
    try using Dof on a very bright day. first at 1.7 then at 22. (or the extreams of you lens) and you should have enough light to see at f/22.
    that make sence?
     
  3. Harpua

    Harpua TPF Noob!

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    Well the mechanics of it make sense to me, but in practical use it does not seem to make sense. It seems that I don't see any difference or it is too dark to see anything. Does this mean the DOF preview will only work on a very bright day?

    BTW thanks for such a speedy response!
     
  4. crawdaddio

    crawdaddio TPF Noob!

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    You just have to train your eye to focus when it dims. Yes it is most easily used when shooting in alot of light. You will learn how your particular lens and camera produce certain DOF's at certain settings with trial and error. Then you will know what (in your image{viewfinder}) to look for when using the DOF preview button. It is a great feature and I wish my dslr had it.
     
  5. markc

    markc TPF Noob!

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    If it's a wide aperture, you won't see a difference, a there isn't any. If it's a narrow aperture, the dof will change, but it will be dimmer. I found the feature nearly useless for my eyes and the kind of light I was often in.
     
  6. doenoe

    doenoe TPF Noob!

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    just try to make a macro of a flower or something. First with the aperture wide open. Hit the DOF preview button and look at the background, you wil see no difference. Then try this with a with a very small aperture, hit the DOF preview again and look at the background. You will notice that the background is more in focus now. But you wont see that when you dont push the button. And you dont push the button just once if you want to see the preview, you keep it pressed the whole time that you want to see the DOF.
     
  7. JonathanM

    JonathanM TPF Noob!

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    If you take this photo as an example
    [​IMG]

    It could really do with less of the image in focus, except the cap, as the grass etc is distracting ie a narrower Dof.

    this image however really needs a wider Dof
    [​IMG]
    ImgFree.net - Hosting Images

    as only a narrow band is actually in focus, with flowers at the fron & rear of the plant out of focus. The only flower in focus is the one with the broken staem facing away from the camera (obvious in the original, les so in the linked photo).
     

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