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06 - Depth of Field part 2


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When you understand what depth of field is, it's much easier to understand how aperture affects depth of field. Contrary to popular mythology, most professional photographers don't walk around in manual mode all the time, they walk around in aperture priority (AV) mode so they can control the depth of field. If the light is good and you have done your 1.5 x focal length calculation and you're satisfied that auto shutter speeds are more than sufficient for sharp photos with no risk of motion blur, aperture priority so you can control depth of field is the way to go.

Unfortunately, aperture priority affects depth of field differently in different lenses. If you're using a wide angle lens at 10mm, f5.6 will probably get everything in a landscape photo in sharp focus. However, if you're using a telephoto at 200mm you may have to go to f16 to get everything in focus. The only way to learn your lenses is to use them. A good way to get to know your lenses is to take a series of photos of the same subject at differing apertures to see how each lens performs.

In the following example I'm using a 50-140mm lens at 50mm taking 3 photos of the same subject, one at f/2.8, one at f/8 and one at f/16. Looking at the photos on my computer I can see how this lens renders the depth of field. From this I can see that if I'm shooting subjects close to the camera and want nice bokeh I need to get as close as I can to my subject and select f/2.8. If I'm shooting landscapes and want the foreground in sharp focus as well as the far distance, I really need to go to f/16.




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In this next example, again with my 50-140mm, I focused on the clock. Seeing how aperture affects the depth of field however isn't immediately obvious and you have to look around the edges of the photo to see what's happening.




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Of course, there are another two factors which also greatly affect the depth of field, and that is the distance of separation between subject and background, and how close you are to your subject. The more you understand depth of field, the easier it is to understand how aperture affects depth of field, and the more you use your lenses, the more you will learn how to control depth of field when out taking photos.

Although a shallow depth of field is generally used to separate a subject from the background, and a wide depth of field is usually for landscapes where everything would be in focus, sometimes you may want to shoot landscapes with a shallow depth of field and shoot closer subjects with a wide depth of field. For me, both of these photos of the seal work well. The first one uses a shallow depth of field which focuses the eye on the seal, but in the second photo I think the background is also well worth looking at as it brings the seal's environment into sharp focus. The first photo was shot using my 200mm prime at f/2 while the second photo was shot at f/16.



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This landscape was shot at 16mm using my 16-55mm. I would more usually shoot this type of photo with everything in sharp focus. With my 16-55mm at 16mm, f/8 does that job very nicely. However, in this case I shot the photo at f/5.6 to throw the background slightly out of focus as I wanted to focus attention on the strand of seaweed, the gorgeous ripples in the calm surf, and the reflections in the foreground. The background being slightly out of focus is unusual for a landscape and gives the photo a kind of painterly feel. Quite a few have remarked that this photo is out of focus or that it has been overly post processed, but it isn't out of focus, the focus is exactly where I wanted it, and the painterly feel isn't due to post processing or editing, it was achieved with clever use of aperture and depth of field.


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