Other than controlling exposure, the aperture setting has another significant effect on your pictures. That is, the depth of field.

To understand depth of field, you need to understand that lenses can focus at only one distance. It could be anywhere between its nearest focusing distance and infinity. The distance that a lens is focused at, is where objects will appear the sharpest. And objects in front or behind that focused distance will gradually become more fuzzy or blurry as their fore/aft distance increases.

The above photo is a good illustration of depth of field. The lens was focused on the part of the barbwire that is in sharp focus, and everything else in front or behind are turned into a nice creamy blur.

Hence, you pick the appropriate depth of field depending on your needs. And you do that by setting an appropriate aperture setting. To get less depth of field, you use a lower f-stop (e.g. f1.8, f2.8), and to get more depth of field, you simply use a higher f-stop (e.g. f8, f11).

When do you want large depth of field?

• When you are shooting stuffs like landscape or architecture, where you want everything in the picture to be in focus.
• When taking group photos. You want enough depth of field to have everyone’s face in focus, especially when you have more than one row of people.

When do you want less depth of field?

• When taking portrait shots, and you want to turn the background into a nice creamy blur.
• When you want to emphasize an object in a photo, by making everything else less focused.

I’ve set the aperture to the smallest number. But I still can’t get that much of a blur.

Different lenses have different aperture range. Some can go as low as f1.2, while others can only reach f4. That is why some of the professional lenses are so expensive. Not only do they contain quality glasses, they allow you to use very low aperture numbers. But of course, there are inexpensive alternatives such as the Nikon or Canon 50mm f1.8 lenses, or f2.8 lenses from Tamron, Sigma and Tokina.

Also, the distance between you and your focused distance plays a part too. At the exact same aperture setting and zoom/focal length, the closer you move in to your subject the lesser depth of field. Of course, this changes your photo’s composition. But it is an important knowledge for times when you are very close to your subject (like a close-up headshot), and you are wondering why only certain parts of the face is in focus, while there is no focus issue when you take a half-body shot.

The simple practical approach

Too much mambo jambo to remember? In the world of digital photography, there’s really no need to memorize all these technical stuffs. Just go out and shoot, and play with the aperture setting to achieve your desired depth of field. Move closer or further from your subject and see how it works out. Nothing beats learning by hands-on. Very soon, you’ll get the hang of it.

Happy shooting!