depth of field preview

Discussion in 'Beyond the Basics' started by Osmer_Toby, Jul 27, 2004.

  1. Osmer_Toby

    Osmer_Toby TPF Noob!

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    how does it work? when i press the button for dof preview on canon 10d, the image through the viewfinder darkens. is this supposed, somehow, to show what will and will not be in focus? :scratch:
     
  2. voodoocat

    voodoocat ))<>(( Supporting Member

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    Yes. It closes down the apeture to what it is set to so you can get the DOF preview. Which also lets in a lot less light. It takes some getting used to.
     
  3. danalec99

    danalec99 TPF Noob!

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    Ditto
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    You have to really look at the parts of the scene that are not near the centre (or near the focus point). Whatever you are focused on will be in focus with or without the DOF button presses or not...just darker.

    The closer/farther parts will be both darker and more in focus depending on how far down the lens is stopping.
     
  5. Osmer_Toby

    Osmer_Toby TPF Noob!

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    so darker=more in focus or vice versa?
     
  6. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Basically that's the way it will work. The smaller your aperture is set the darker it will get when you press the DOF button. Of course the smaller your aperture...the greater your DOF will be.

    Although, you can't make the direct connection that because it's darker it will be in focus. That depends on the actual DOF of the lens at that particular aperture.
     
  7. Osmer_Toby

    Osmer_Toby TPF Noob!

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    ahhh. so dof preview simply shows you the brightness of the exposure, not what's ultimately going to be in focus.

    do i have that correct?
     
  8. voodoocat

    voodoocat ))<>(( Supporting Member

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    No, it does show you what will be in focus. It will just be darker due to less light entering the lens. It was definately hard to get used to when I first got the D70. But now I'm using hyperfocal and doing a quick check with the DOF preview.
     
  9. photobug

    photobug TPF Noob!

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    Toby, to really illustrate this you need a brightly lit subject. Like a line of cars on the street at noon or something.

    Line up a shot down the line of cars. Focus on the third car in line. Notice how many of the cars appear to be in focus. Set your aperture at f/8. Hit the DOF preview button. How many cars are in focus now? Try it at f/16.

    The viewfinder darkens because the camera normally meters at full aperture and stops the lens down just before the shutter trips. When you use the DOF preview you're manually closing down the aperture, so the viewfinder gets darker. Assuming there's enough light you also can see how much of the view is going to be in focus.

    You really have to do it in bright light so you can see the effect as the viewfinder darkens. After awhile it becomes second nature.
     
  10. grooski

    grooski TPF Noob!

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    Well by pressing down the depth-of-field preview you see what depth there is. Well to see what depth you have you must have an f/stop such as f/16, f/5.6, etc. When you press the preview it simply just closses the aperture ring to the designated f/stop you put in. Why it gets dark? It gets dark because the larger the f/stop meens that there is a smaller hole and if there is a smaller hole that makes it so less light gets in. Does this answer your question? Oh and yes it does show what will be in focus even though it is hard to see with a larger f/stop. Oh and remember the larger the f/stop the more depth or whats in focus.
     
  11. jadin

    jadin The Mad Hatter

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    Using DOF preview drains my battery like nobody's business. I know 'roughly' how much a given aperture will provide and work from there. Works for me anyway.
     

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