The difference a portrait lens makes
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
Selecting the right focal length
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 those with a focal length over 85mm.
Let's look at some shots to demonstrate what you can achieve with the 18-55mm lens that comes with most EOS cameras, compared with a specialist portrait lens.
At this classic distance for a head shot, the specialist lens offers a greater focal length to give a more natural look and separate the model from the background.
We have shot each of them at the same aperture, it is only focal length that changes. Look at the shape of the models face in the first image compared to the other two and also how the background compresses when using the longer focal length. In the 24mm shot the models face appears distorted whereas it feels more natural in the 70mm and 135mm shots. Also the background is far more noticeable in the 24mm shot compared to the 135mm.
A bigger aperture helps
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 setting an aperture available with the kit lens, compared with portrait lenses.
The picture on the right is taken with a wide aperture, only available with a specialist lens, so the model stands out from the busy background. The aperture also helps with the lightness of the shot.
These three images are all shot at the same focal length and exposure with just the aperture size varying from small in the first shot to large in the third shot. When trying to eliminate distracting backgrounds in portrait photography, having a large aperture lens is essential. In the third image the viewer's attention is directed away from the distracting background and onto the model's face and is a far more effective portrait.
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