Analyzed: Effective Depth of Field

Depth of field is a major element of photography. To most people, a razor-sharp subject and an extremely out of focus background (also known as “bokeh”) is a pleasing effect, isolating the subject with indiscernible surroundings. I personally am a huge fan of bokeh; something about the surrealistic dreamy glow of distant, out of focus lights or glares is extremely appealing to me.

I won’t go into the technical details, but essentially the fuzzy background comes from an extremely shallow depth of field. The shallower the depth of field, the fuzzier the background. Shallow depth of field is the result of shooting with a wide aperture. The wider the aperture, the shallower the depth of field, the fuzzier the background. Ironically, aperture width is inversely relational to the f-stops; the smaller the f-stop, the larger the aperture.

My dad has been letting me use his DSLR, a Canon EOS 40D, and for the most part I use the Canon EF 28-135mm f/3.5-5.6 IS USM lens that came with it as part of a kit.

I was baking cookies today, and silly me still hasn’t learned to preheat the over before mixing ingredients, so while I was waiting for the oven to preheat, I decided to play with some aperture settings.

What a difference: ISO 100, f/5.6 (2″) on the left, f/36 (30″) on the right.

(Click the photo to see the full resolution image – 10.1MP, 3888×2592)

The above photo is a composite of two photos taken of exactly the same scene. I’d set my camera to Aperture Priority using ISO 100 (for the lease amount of noise) and “Shade” white balance, so the only factor I changed was the aperture, the camera automatically set shutter speed for me. Some things worth noting:

  • f/5.6 is almost as wide as the lens barrel, f/36 is practically a pinhole.
  • Small f-stop: more light is let in, less exposure time necessary, but focus is softer.
  • Large f-stop: less light let in, longer exposure time necessary, but focus is sharper.

At close-range like this, the change in aperture setting is very apparent. Even stepping from f/5.6 to f/6 made quite a difference.

I just wanted to see the stark difference side by side. :)