DigitalCameraReview.com
FPT: How to Create Depth of Field
by Laura Hicks -  8/16/2013

You see it all the time in professional portraiture - that mixture of a perfectly in-focus subject and a smooth, soft background. You love the look, but you're not sure how to get it. Trust me, it's easy. In just a few short minutes, you'll be shooting like the pros.

Creating depth of field in your imagery is a mixture of several elements including focal length of the lens, distance from the lens and the aperture of the lens. Together, these factors will help you to create an image that either has a shallow depth of field or a narrow depth of field.

Aperture
Before we get to the how-to part of this article, I'm going to give you a quick lesson about aperture. Aperture is the opening in your camera's lens that controls the amount of light that enters your camera. In photography, aperture is referred to as an f-stop. I'm sure you have seen numbers like f/1.8 or f/16. These numbers tell us about the opening of a lens and how much light will enter that lens. For example, if we say we are using an aperture of f/1.8 it means quite a bit of light is entering the camera by way of a large opening in the lens. On the other hand, if we say we are using an aperture of f/8, we are restricting the amount of light we allow to enter the camera because the opening of the lens gets smaller. That's the tricky part--in photography, the bigger the aperture, the smaller the number. For example, an aperture of f/1.8 is considered wide. It will allow more light to enter the camera and will also render a larger percentage of the image out of focus. F/16, on the other hand, is considered narrow and renders a larger percentage of the image in focus.

Below is a sampling of images at various apertures ranging from f/1.8-f/16.

f/1.8/ 50mm /ISO 400                                                  f/2.8/ 50mm /ISO 400 

f/3.5/ 50mm /ISO 400                                                  f/4.0/ 50mm /ISO 400 

f/5.6/ 50mm /ISO 400                                                  f/6.3/ 50mm /ISO 400 

f/7.1/ 50mm /ISO 400                                                  f/8.0/ 50mm /ISO 400

f/13/ 50mm /ISO 400                                                  f/16/ 50mm /ISO 400  

The biggest difference can be seen when comparing f/1.8 side-by-side with f/16.

f/1.8/ 50mm /ISO 400                                                  f/16/ 50mm /ISO 400

Lenses
Before we move on let's talk quickly about lenses and their apertures. Many prime (fixed focal length) lenses have maximum consistent apertures starting around f/1.4, f/1.8, f/2, or f/2.8. This makes them a great option for portraits since they can produce images with shallow depth of fields. They can be found in a multitude of focal lengths generally ranging from 8.5mm to 600mm. Zoom lenses can also be found in a myriad of focal lengths and aperture ranges. Zoom lenses can either have fixed maximum apertures or variable apertures. If the lens has a variable aperture of f/3.5-f/5.6 for example, the lens will adjust the maximum aperture as it travels through the focal lengths. However, if the lens has a constant aperture of f/1.8, then the lens can use that same maximum aperture no matter what focal length you are using. As a general rule, zoom lenses that have a constant wide aperture are more expensive than those that have a variable aperture. 

How-To
Setting your camera for a shallow depth of field:

If you have a point and shoot camera, do not despair. You can still produce images with a shallow depth of field. Many modern PNS cameras have a scene setting called "portrait." This mode tells the camera that you are interested in a defocused background and will set the aperture to the widest possible setting. Also, putting distance between your subject and your background will also give you a more defocused look.

Have a great weekend and go grab that shot!