Congratulations on taking the giant photographic leap to an interchangeable lens camera! Sure, your phone has served you well (and will likely continue to do so) but now it’s time to spread your picture-taking wings. And as cool as your new DSLR or mirrorless camera is now, it won’t reach its true potential until you take a deep dive into the world of lenses. It’s a somewhat sad fact that most interchangeable-lens camera buyers never take off the kit lens that came with the camera, which sort of defeats the purpose of having an interchangeable-lens camera. This is why we’ve put together this guide to help make sure you know what to look for in lenses, and thus get the most out of your new camera.
Your first step
If you’ve yet to pull the trigger on a new camera, make sure to check out the lens options available for the brands and models you’re researching. Sure, it’s unlikely that anyone needs to buy a dozen lenses for their camera, but the larger the collection available, the more variety you will have to choose from, from wide-angle to telephoto and everything in between. Above all, make sure the specific type of lenses you need for your personal photographic style are available for your system of choice. For example, if you primarily photograph landscapes, you’ll want a different type of lens than if you plan to shoot mostly portraits (we’ll get into the specifics in a minute).
When you buy an interchangeable lens camera you’re entering a relationship with the specific hardware mount determined by the brand, so this is not a choice to take lightly. For example, Nikon DSLRs use the F mount and Canon DSLRs use the EF and EF-S mounts. Canon’s EOS-M series mirrorless cameras use a completely different mount, called EF-M. With the exception of Panasonic and Olympus, who share the Micro Four Thirds mount, virtually every manufacturer sticks to its own mount. And while they are all interchangeable-lens cameras, you cannot use Nikon glass on a Canon body and vice versa (well, sometimes you can but this involves using a mount adapter and almost always sacrifices some functionality).
Beyond the basics
DSLRs and mirrorless cameras — particularly entry-level models — are often sold in “kits,” meaning they are typically supplied with a basic zoom lens, which may be something like an 18-55mm or 14-42mm depending on the brand and format of your camera. One common misconception about large, interchangeable-lens models is that they offer inherently better zoom capability than a compact camera. In fact, the opposite is often true. An 18-55mm lens is only a 3x zoom. Compared to a compact like the $400 Canon PowerShot SX730 HS, which has a 40x zoom (over 13 times the zoom power of a DSLR kit lens), this is nothing.
Typically, the maximum zoom power you’ll find in an interchangeable lens is around 10x, but comparing a DSLR or mirrorless camera to a point-and-shoot isn’t really fair. These cameras use much larger sensors that produce very high quality images compared to compact models, but those large sensors require equivalently larger lenses. This is why small cameras can have oodles of zoom, while larger cameras will rely on multiple lenses to cover the same range.
The numbers game
Don’t put your phone away just yet; we’re going to need the calculator. Although a lens’ focal length may be 14-42mm, 18-55mm, 28-80mm, and so on, these numbers can’t be directly compared to each other across different formats. The actual angle of view that you’ll capture is impacted by the size of the imaging sensor, with the most common sizes (or formats) being full frame, APS-C, and Micro Four Thirds. (There are also medium-format cameras, but those are for the pros.)
In order to understand what a lens will look like on one format compared to a different lens on another format, we need to convert those focal lengths into some kind of standard. The industry agreed-upon method for doing this is to use the full frame equivalent focal length, which is calculated using a format’s crop factor.
Most APS-C sensors have a crop factor of 1.5x, which means if you multiply a lens’ focal length by 1.5, you will get the full frame equivalent focal length of that lens. (Canon is an oddball here, with a crop factor of 1.6x on its APS-C cameras.) For example, an 18-55mm kit lens on a Nikon D5600 will have a full frame equivalent focal length of 27-82.5mm. The Micro Four Thirds format is a bit smaller than APS-C and has a 2x crop factor, so a 14-42mm MFT lens will have an equivalent focal length of 28-84mm. Notice anything about those numbers? Exactly: An 18-55mm APS-C lens provides just about the same field of view as a 14-42mm MFT lens. Across manufacturers and formats, basic kit lenses cover roughly equal zoom ranges and fields of view.
So, why is this important? In the days of 35mm film, most cameras used the same size recording medium, and so when looking at the focal length of a lens, the user immediately knew what angle of view it would capture. A 24mm lens was always a wide-angle, a 50mm was always a “normal” lens, and a 24-70mm zoom would always cover everything from wide-angle to short telephoto.
Nowadays, the only instance where the stated lens focal length is one-for-one are cameras with full-frame sensors, such as the Nikon D750, Canon EOS 5DS, or the mirrorless Sony Alpha A7 series. In these cameras, the sensor is the same size as a frame of 35mm film. This is why you will often see “full frame equivalent” written as “35mm equivalent.” We stubbornly prefer the former in order to avoid confusion: Saying an APS-C 35mm lens has a 35mm equivalent field of view of 52.5mm is just a mess.
When buying lenses for your new camera, you always have to keep in mind how the size of the sensor impacts the angle of view of the resulting images. Using a “nifty fifty” 50mm f/1.8 lens on a Canon Rebel T6i will not yield a “normal” angle of view as it will on a full frame camera. Instead, it becomes a moderate telephoto at around 80mm due to the 1.6x crop factor. Likewise, on a Micro Four Thirds camera, a 25mm lens is not a wide-angle, but equivalent to a 50mm lens due to the 2x crop factor.
Once you’ve decided on your format, you don’t really need to worry about equivalency anymore. Slap a lens on your camera and what you see is what you get. However, when comparing formats, understanding crop factor isn’t just about knowing what you’re talking about; it can actually save you money and help make sure you’re picking the right camera system for your needs. Don’t look at a $350 25mm f/1.8 Olympus lens and think, “Wow, this is way less expensive than the $750 Nikon 24mm f/1.8.” These are completely different lenses. Instead, compare the Olympus 25mm f/1.8 to Nikon’s 50mm f/1.8, and you’ll discover that the Nikon is actually much cheaper — just $220.