Behind the Lens: Aperture setting can be used to manipulate depth of field


This photograph of my wife holding a dragon for Chinese New Year demonstrates a creative use of a camera’s aperture. By selecting a large aperture, represented by an f/stop number of f/2.0 on the camera, and focusing only on the dragon, I created a very shallow depth of field, throwing the entire background out of focus.

The typical camera has a control dial on top. Last week I reviewed how setting this dial to “S’ “T” or “Tv”, controls the shutter speed. The other primary controls on this dial are “A” or “Av” for aperture priority, “P” for program, and on some cameras, “M” for manual.

Honestly, most people don’t know an aperture from an aperitif. If you do, consider yourself a well-schooled photographer.

For those who need a refresher, the aperture is basically an opening through which light travels. Like shutter speeds, different sized apertures control the quantity of light entering your camera. If you think of your camera and lens as a window with curtains, your aperture is the size of your curtain opening and the shutter speed is how fast you open and close the gap in the curtain.

One of the reasons people don’t pay much attention to the aperture is because on small-sensor, point-and-shoot cameras, aperture choices have little noticeable effect on photographs.

The effects of shutter speed, however, can be very apparent. A fast shutter speed enables you to capture the movement of your daughter playing soccer, but if a shutter speed is too slow it can blur a portrait of your sleeping dog in low light.

For these reasons, with P&S; cameras, I recommend setting cameras to “S” to give you control over shutter speed and adjust to slower or faster shutter speeds as light and subject change. In “S”, shutter-priority mode, the camera will automatically select an appropriate aperture, based on your shutter speed choice, to determine a correct exposure.

If you shoot with a 35mm single-lens reflex camera, which has a larger sensor size, the aperture can have a greater effect on the look of your photographs — something known as “depth of field” (DOF).

Depth of field represents an area of your image, in front of and beyond your point of focus, that will also remain in focus.

Professional photographers use different apertures to make creative use of DOF.

On all cameras, if you are selecting apertures by menu or dial, you see numbers like this: f2.8, f4.0, f16. These numbers, also called f/stops, represent different-sized apertures. Simply put, the larger this number, the greater your depth of field — f11.0 would give you greater depth of field than f2.8.

However — and this is a little confusing — the larger an f/stop number, the smaller the aperture. While numerically f/22 is larger than f/8, these numbers represent fractions like 1/22 and 1/8, and therefore the confusion. Here is what’s important to keep in mind.

• Larger f/stop numbers (f16, f22) equal smaller apertures, which can create greater depth of field. If you or your camera selects a large f/stop, there is typically lots of available light or you are taking very long shutter speed exposures.

• Smaller f/stop numbers (f2.8, f4) equal larger apertures, which means less depth of field. If you or your camera are selecting small f/stops, there is probably very little available light or you are using very fast shutter speeds.

I’ll continue this subject next week and show how to make effective use of your aperture for creative results.


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