DSLR Photography 101: Choosing a Lens

Megan O'Neill


Over the past few weeks, we’ve been exploring DSLR photography. So far, we’ve taken a look at ISO, shutter speed, and aperture. After the basics, one of the most common questions about DSLR photography is “which lens should I buy?” That’s why, today, we’re taking a look at the different types of lenses and how to choose a lens that best suits your needs.

Why your sensor size matters

The first thing to consider when selecting a lens is your camera’s sensor. Depending upon whether you’ve got a full frame sensor (equivalent to the size of the traditional 35mm film frame size) or a smaller sensor (also known as a crop sensor), the way a specific lens performs will differ.

Cameras with full frame sensors will present the same field of view at a given focal length as a traditional 35mm film camera. However, cameras with smaller sensors will change the field of view at a given focal length by effectively cropping the image and therefore increasing the effective focal length of your lens, making it act like a longer lens. This is illustrated in the image below, created by our Consumer Customer Owner, Beth Forester.

Full Frame Crop DSLR Photography

Cameras with crop sensors are given a crop factor so that you can calculate the effective focal length of a given lens. You’ll multiply the focal length of the lens you are using by the crop factor to arrive at the effective focal length that you will see in your photo. For example, if your camera has a crop factor of 1.3 then a 100mm lens would actually represent an effective focal length of a 130mm lens (100 x 1.3=130).

Note: For the remainder of this article, we’ll be referring to lenses and focal lengths in relation to a full frame sensor.

Standard and kit lenses

When you purchased your DSLR camera, it may have come with a “kit” or starter lens. Kit lenses vary according to camera and manufacturer but they are referred to as “kit” because they are sold together as part of a package (or “kit”) with the camera body and accessories you need to get started with DSLR photography.

Generally, most kit lenses sold as part of a package are zoom lenses that fall within the standard (or normal) focal range of 35-70mm. Lenses with focal lengths in the range of 35-70mm are often referred to as “standard” or “normal” because they are closest to to the perspective or view of the human eye. A 50mm lens is generally considered the closest to human sight.

Understanding that the standard lens is closest to normal, human sight, will make it easier to understand the other types of lenses, which allow you to capture a wider area of a scene than the regular eye would, or to magnify far away objects so that you can see them closer and more clearly than you’d be able to with an unaided eye.

Focal Lengths

So if a standard lens is in the ballpark of 50mm, you’ll get a different effect when you use a lens that’s either longer or shorter. Shorter focal lengths result in a wider angle of view and less magnification, while longer focal lengths result in a narrower angle of view and more magnification. Focal lengths fall into 3 major categories: wide (20-35mm), standard (35-70mm) and telephoto (70-1200mm).

The images below, shot by Beth, show how the same subjects look through different lenses. These images were all photographed at the same distance away from the subjects, approximately 40 feet.

Focal Length DSLR Photography

Prime vs. Zoom Lenses

Lenses fall into two types, prime and zoom. Prime lenses have one fixed focal length while zoom lenses have variable focal lengths, meaning that you can adjust them to zoom in and out on your subject, changing your focal length and angle of view.

Prime lenses usually have larger maximum apertures, which can be helpful in low light situations. Popular prime lenses are 35mm, 50mm, 85mm, though zoom lenses tend to be more popular because of their versatility.

Zoom lenses can fall within one focal length category or span multiple focal length categories. For example, an 18-35mm zoom lens would be strictly in the wide range, while a 24-70 mm zoom would fall within both the wide and standard rages. Some zoom lenses can even fall within three ranges, such as the 24-105mm lens, which covers wide, standard, and short telephoto. Beth commonly carries the 24-105mm when traveling. She uses the shorter 24mm option for landscapes and the longer 70-105mm range for taking photographs of her family.

Some common lenses and their applications

Fish Eye Lens – 18mm or less

Sometimes referred to as a super wide angle, this lens is usually used for unique effects and in super tight spaces.

Wide Angle Lens – 20-35mm

This lens has a short focal length that captures a wider view. It is useful for landscapes, for architecture, or for situations where you may want an area to look larger or more spacious, as in interiors.

Telephoto Lens – 70mm and above

These lenses have long focal lengths that result in magnification of the subject and are useful for sports and wildlife photography.

Macro Lens – 100mm, 200mm, 60mm prime lenses are popular choices

Macro lenses magnify your subject and allow for focusing at closer distances — with a macro lens you can achieve focus at as little as a few inches away. Macro lenses are useful for shooting extreme close ups of small objects like insects or for capturing small details of a larger subject like flowers.

Join us next week when we dive deeper into lens selection and how various focal lengths affect your portraits.

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