Aperture & DOF Rule of Thumb?

Discussion in 'Beyond the Basics' started by Neuner, Aug 7, 2007.

  1. Neuner

    Neuner TPF Noob!

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    I think the best way to explain my question is with an example. I took portrait shots of my two little girls using a 50mm at f1.8 on my D80. Even though I set them next to each other, because of their squirming and playing around, they were not of equal distance from me. The one closest too me was in focus and the one set slightly further back was not. I lost some really cute shots of them because of this. Is there a rule of thumb as to what the DOF will be for an aperture setting? I like to have the lowest aperture but have a DOF deep enough to have both of them in focus with a blurred background.

    Thanks!
    Neuner
     
  2. Stranger

    Stranger TPF Noob!

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    im not 100% if there is a rule of thumb, if so i have never read it.

    What you should really look for is the subjects distant from the background.
    The sharpest aperture on your lens is about 2 stops down from wide open. So if the background is quite a ways away, dont stop yourself from going to f/5.6 or so if the lighting calls for it. That will still throw the bg out of focus if they are not right next to it. but at the same time be good enough to keep them in focus.

    Shooting at 1.8 and focus on the closest eye is usualy shallow enough to throw the back eye out of focus a bit so when shooting two people i would def close it down a bit.

    hope that helps
     
  3. JenR

    JenR TPF Noob!

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    Your depth of field is related to your focal length, your aperture, and the distance to your subject. Here is an online calculator....

    http://www.dofmaster.com/dofjs.html


    If I am trying to do a portrait of two small kids together, I will typically shoot in the range of f3.2. It works for me; but your situation may be very different.
     
  4. lifeafter2am

    lifeafter2am TPF Noob!

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    What camera do you have? On mine (30d) there is a button that lets you preview the DOF. I have never used it, but it seems interesting.
     
  5. Big Mike

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

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    You DOF will be different, depending on the distance to the subject, the aperture setting, the focal length of the lens etc. You can probably find a DOF chart for that lens, which would help you to get an idea of what DOF you are looking at, based upon the variables of your shot.

    You could also use the DOF preview button, if your camera has one. When you press the button, the lens stops down to the shooting aperture and the DOF will be discernible. The viewfinder does get dimmer and it's often hard to tell exactly. Of course, this isn't' something that you can do with squirming subjects but it should give you an idea.
     
  6. Neuner

    Neuner TPF Noob!

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    Thank you! I will try your settings and see how they turn out. I've tried to play around with the DOF button, but I don't get it...
     
  7. Neuner

    Neuner TPF Noob!

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    Excellent - thanks. I searched and found the following website that may also help others. It will produce a chart for your camera & lens focal length: http://www.dofmaster.com/doftable.html
     
  8. deanimator

    deanimator TPF Noob!

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    There´s a point called "hyperfocal distance"...it´s kind of in the middle of the zone which appears to be in focus.

    What may help is, borrow a manual SLR with a 50mm lens.
    Look at the lens barrel...for the focus point.
    There will be a ring of numbers corresponding to f-stops on either side...this helps see the RANGE of focus or Depth of Field.

    Look at these examples I have quickly made using an old manual camera:

    f4 A nice aperture for portraits with a 50mm lens. If you select f4 and focus at 3.8 metres, you can see the marked DOF...just to the left and just to the right of the focus point is the number 4. ...look at the distances it corresponds to: it means that everything between 3m and 5m is in focus. Try changing the focus point to say 15m and you will see the DOF is from 8m to infinity.

    [​IMG]

    f16 For this aperture you will need good light or a tripod. But it offers you a good (long) DOF. Selecting f16 and again focusing on 3.8m...now look for the 16 on the left and right of the focus point, and check out what the corresponding DOF is: you can see that everything from 1.8m to infinity is in focus. If you set your focus at infinity to shoot a landscape, you will find the DOF is only 3.5m to infinity so that things or people close to the camera are not sharp. (this mistake is commonly made).




    [​IMG]
     
  9. Digital Matt

    Digital Matt alter ego: Analog Matt

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    You won't see a change in your viewfinder if you are shooting wide open. In this case, you are already previewing the depth of field. The lens will always be wide open until you shoot, regardless of what aperture you are set at. When you press the DOF preview button, it stops down to the aperture you are shooting at to give you the preview.
     
  10. deanimator

    deanimator TPF Noob!

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    Make sure you have set the exposure type to either aperture priority or manual. Then select f16 and focus on something 4 metres away. Press you DOF preview button...the screen or better, the viewfinder, should become noticeably darker, but you should see that nearer things are sharper.
     
  11. deanimator

    deanimator TPF Noob!

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  12. Neuner

    Neuner TPF Noob!

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    Wow, thanks for all of the help! I've read through that thread before, it's very informative.

    I'm anxious to give it another try this weekend. Hopefully I have the time and my girls are in a good mood...
     

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