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Focussing for Depth of Field

Control depth of field to make images "pop"!

Focussing for Depth of Field (DOF) - Depth of field is the term used to describe the amount of your image that is in focus. Landscapes, for example, where everything is in focus have good or deep DOF. A macro shot, where only a small part of the image is in focus has poor or shallow DOF.

Focussing for Depth of Field

Depth of field is generally determined by the aperture setting with larger apertures of say F2.8 giving shallow depth (not much in focus). Small apertures of say F16 give deep or good depth of field (most of the image in focus).

By closing the aperture to its smallest setting of say F32, you won’t actually increase the depth of field. This is because some of the light rays passing through the aperture become diffracted at very small apertures causing poorer quality.

The lens that you use also plays a massive part in creating depth of field.

Focussing For Depth of Field - The Effect With Different Lenses

Many people don’t realise that the type of lens you use has a definite effect on the depth of field. The why’s and wherefores of how this works are for a more advanced book and aren’t particularly important at this stage.

What you do need to know however is the effect that each lens has.

  • Wide angle (10-24mm) - Due to the amount of coverage that these lenses give, even with larger apertures of around F2.8, most of the image tends to be in focus. To create some depth of field using a wide angle lens you can simply bring the main subject closer to the lens. To illustrate this point we can use an awesome tool called a depth of field calculator over at dofmaster.com. Open it and try these entries:
  • 1
    Camera - Canon EOS 1D Range
  • 2
    Lens focal length - 16mm
  • 3
    Selected aperture - F2.8
  • 4
    Subject distance - 20 feet

You would think that with this aperture of F2.8, you would get a shallow depth of field, but by using the calculator you will notice that the results are quite amazing. The closest depth of field coverage is from less than 8 feet in front of you to infinity (and beyond)!

The other extreme

Now, the other extreme, just change the subject distance to 1 foot and notice the difference. The DOF is severely reduced to just 0.15 feet in total!

  • Telephoto (200-500mm) - Because a telephoto lens is drawing the subject closer, the knock on effect is that the DOF greatly reduces as the lens gets larger. Again, using the calculator, try these entries;
  • 1
    Camera - Canon EOS 1D Range
  • 2
    Lens focal length - 500mm
  • 3
    Selected aperture - F16
  • 4
    Subject distance - 50 feet

Here you would think that by using an aperture of F16, most of the image would be in focus. Wrong! The calculator shows us that the total distance in and around the subject which is in focus is just 2.17 feet.

So the basic rule applies that a large aperture gives shallow depth of field and a small aperture gives great depth of field. Therefore, always bear in mind what lens you are using and the effect it has.

Once you understand the basics of DOF, you can incorporate it in much of your photography whatever the subject. It should be always on your mind what apertures and lenses you are using and what effect they will have on the clarity of your photos.

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