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Lesson 3: Discovering Depth of Field Part 3. Focal Length

close proximity creates a shallow deth of field.
Lesson 2: Discovering Depth of Field
10th January 2020
Ten questions you should ask about your business and the photography you use.
27th January 2020
45 mm shot

45 mm look at the background.

Lesson 3: Discovering Depth of Field. Part 3. Focal Length

Shallow depth of field image of a starling

Last time and in lesson one we looked at Depth of field; how much of the picture is in focus. We have seen how this is affected by the aperture and proximity to the subject.The final part (for now) about depth of field involved using a zoom lens.

You will need:


A subject of your choosing.
A camera with a zoom lens.

Camera Settings


Set your camera into Aperture Priority (A or Av mode) if you have it and put ISO on Auto. Set the camera to its widest aperture. This will be the lowest f/ number. So set your camera to f/4 or f/3.5 or even lower if you can. We looked at this in the last lesson. You don’t want f/18 or f/22.

Practice zooming in and out with the lens. On a DSLR or mirrorless this is usually turning a ring on the outside of the lens barrel. On compacts and bridge cameras one usually has to press a toggle button to zoom in and out.

(N.B. Zooming in makes the subject look closer and zooming out makes them look further away.)

45 mm shot
45 mm look at the background. Iy is out of focus and slightly blurred. The bow appears to be sharp.
depth of field changing with the focal length
At 200mm, the background appears much more blurred. The bow is a little bit blurred.
depth of field changing with the focal length
At around 400mm, the background is very blurred and the bow is getting more unsharp. Much more fine detail is also visible than the first shot.

Take the shots

Look at a subject, such as a person, through the camera and zoom out – making them appear as small as possible. Make sure you include a background well behind the subject. Take the shot.

Don’t change position, but zoom in and take another shot

Compare these two shots photos. The one taken zoomed in has the most blurred background, the one shot zoomed out will have more of the background in focus.

In a way, this is an illusion. If you take the zoomed out shot and crop it using editing software so the photo looks the same as the zoomed in shot. The background should be blurred to the same amount. We’ll look more at this in later lessons.

Practice this and Let me see your shots! Add a comment below and/or share them with me on facebook or Instagram using the links in this page’s footer below and add the hashtags#ivorphoto and #ivorslessons and tag me @ivortog.

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