Most EOS cameras come with a general purpose kit lens that works for most types of photography. There are, though, a series of specialist lenses designed for specific genres, like portrait photography, for instance. These can make a huge difference to your photos. With portrait lenses, the main difference is with the focal length and maximum aperture.
Focal length is the distance between the lens and your camera sensor when the subject is in focus, and is stated in mm. Zoom lenses have a focal range which is written as minimum and maximum such as 18-55mm. Typically, a portrait lens refers to a lens with a focal length over 85mm.
In this classic head and shoulders composition, the specialist EF 85mm f/1.8 USM portrait lens offers a greater focal length to give a natural look and to separate the model from the background.
In comparison, using a shorter focal length such as 24mm would distort the subject's face by appearing to alter its proportions. Also, backgrounds are usually more noticeable at shorter focal lengths.
Another key factor in selecting a lens suited to shooting portraits is its maximum aperture. Aperture refers to the size of the lens opening that lets in light to your camera sensor.
Each lens is given an aperture rating such as f/2.8 or f/5.6. Some zoom lenses have an aperture rating depending on which focal length is selected; these will show an aperture range such as f/3.5-5.6. The smaller the aperture number, the larger the maximum opening and there are advantages to shooting portraits on a lens with a larger maximum aperture.
A bigger aperture lets in more light through the lens into the camera, so large aperture lenses are great for shooting in low light such as indoor portraits. A second benefit is that shooting with the aperture set to its maximum value, often referred to as “wide open”, produces more background blur often favoured by portrait photographers.
Let's take a look at some examples of taking portrait photographs at different apertures, using the Canon EOS M5 with a Canon EF-M 32mm f/1.4 STM lens.