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07 - Depth of Field part 3


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Before taking a photo it's important to think about your depth of field. This is why most photographers walk around in aperture priority when the light is good. If the camera is automatically selecting fast enough shutter speeds that we don't have to worry about motion blur, then we can put our cameras in aperture priority and concentrate purely on depth of field.

If we're taking a landscape shot then most times we would want a wide depth of field with everything in focus so we would stop down our apertures to widen the depth of field. If we want to isolate something close to the camera we would want a shallow depth of field to focus attention on our subject.

In these two photos taken at the same time we have a balancing stone sculpture set against Sputie Waterfall. The stones are clearly the subject. In the first photo, taken with my 200mm lens, the aperture is at f/8. In the second photo the aperture is at f/2.8. I did try f/2 but the depth of field was too shallow and some of the balancing stones were not completely in focus. I had to stop down the aperture one stop from f/2 to f/2.8 to widen the depth of field slightly so all the stones were nicely in focus.

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Now you can test the power of aperture and depth of field for yourself. Look at the first photo and you will notice your eyes don't stay on the stones, but keep wandering into the background. The grass and twigs and the waterfall are distracting and compete with the stones for attention. If you look into the background in the second photo you will find your eyes want to go back to the balancing stones sculpture. This isn't an optical illusion, it is the power of depth of field. Rather than compete with the sculpture, the background now complements it very nicely. In this case, a very slight dark vignette also helped.

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Here's another example of why being in aperture priority so you can control depth of field is important. This time I used an oriental poppy which appeared in my garden this week as my subject.

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The first thing I decided was I wanted to fill the frame with the flower. As I don't have a macro lens, I opted for my beloved Fuji 16-55mm, got as close to the flower as I could so the lens would still focus (which is 30 cms or about 1ft) then zoomed all the way to get as close as possible. That gave me a sufficiently large file to take a 3500 pixel wide crop and fill the frame.

My first attempt was at f/2.8. However, when I checked the image at 100% most of the flower was out of focus. The full sized image looked okay, but when you zoom in you can see the problems due to the depth of field being far too shallow.

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My next attempt was at f/11. Again, the image looked okay until you zoom in to check focus. It's much better, but there is still too much of the flower out of focus.

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My next attempt was at f/16 and that did the job very nicely indeed. All the flower was in sharp focus right across the image, corner to corner. Here's my final image, which I'm delighted with.

flowerdof02.jpg.97a143c06faa227406680d366ddb46ec.jpg

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