Wide aperture is best for portraits

When shooting portraits, whether of people or animals, your subject should be the main focus of the picture and the best way to achieve this is to use a wider aperture. This will keep your subject sharp, while blurring out any distractions in the background.

Keep in mind that a smaller f/ number means a wider aperture and the wider the aperture, the more dramatic this effect will be. Some lenses can go as low as f/1.2, but even apertures of f/5.6 can do the trick. To better understand how the aperture affects your images, switch to Aperture Priority Mode (Av or A) and try taking some shots with different apertures.