If you have tried to accomplish a shallow depth of field in camera, but are still not successful, you may want to consider buying a new (or used) lens to help you with it.
A zoom lens is a great way to get a shallow depth of field. Most zoom lenses will give you a variety of focal lengths. Different maximum apertures at different points on the spectrum for focal length will be on many of the zooms you use. For example, a 55 mm lens would give you maximum aperture of f5.6 while the 18 mm would give you maximum aperture of f3.5 if you go with an 18-55mm kit lens. Many people seem to think that 18 mm end of the range will give the best blurry backgrounds and focal length because of the bigger aperture. The only problem with that idea is that the 18 mm shoot set a wide angle which means, if you’re shooting a portrait, you will need to be very close to your subject, potentially distorting the features on their face.
I personally prefer to shoot at the 55 mm end of the lens. This allows me to stand back farther, thus making my subject feel more at ease and causing the background to be further away from where I am shooting. Even using the fastest aperture around will still get you a blurry background. A zoom lens will also give you the ability to fill up your frame with the subject, putting the focus where it should be.
Of course, not everyone can go out and purchase a new lens to get the shallow depth of field they desire. It can be hard to add that into your budget. Just remember, maximum apertures are provided by different lenses. The ones that are larger and faster allow you to make your depth of field smaller. It also gives you the opportunity to shoot in situations of low light without the need of a flash. My favorite for the Canon DSLR is the Canon 50 mm f/1.8 lens that I use. It is great for portraits with its good focal length, it is very fast, and one of the more affordable lenses made by Canon.
If you are in the market for a new zoom lens, take your time and shop around. While the kit lenses can get you more variety, you may want to consider a fixed lens, depending on your needs.