2. Full-Frame vs. Crop Sensors
Even if you’re new to the world of digital single-lens reflex (DSLR) photography, you’ve probably heard a comparison between full-frame and crop sensors. It might not have meant much to you when purchasing your first camera, but it certainly means a lot in regard to the use of lenses and your future lens purchases.
A full-frame sensor is the same size as a 35mm film frame—just think of the film shot in many pre-digital cameras. You can find full-frame sensors in Canon camera models such as the 6D, the 5D (all versions), the 1D-X, and all of the older 1D-S models. For those photographers moving from film SLR cameras (and many other types of cameras) to a DSLR, a full-frame sensor does not affect how you use your lenses and see your images, and you can more than likely use the same lenses, as long as they are designated as EF glass. For many, a full-frame sensor is much desired for many reasons beyond how it correlates with the use of our lenses, particularly among portrait and landscape photographers and photojournalists.
A crop sensor shares the same rectangular perspective (often referred to as the 3:2 ratio) but is considerably smaller. How much smaller? For Canon crop-sensor cameras, a bit more than 50 percent smaller. At the time of writing, Canon makes only one size of crop sensor, known as an APS-C sensor (Figure 1.5). These sensors can be found in anything “below” the 5D lineup, such as the Rebel series, the 70D (and its previous iterations), and the 7D. Up until a few years ago, Canon also manufactured another, larger crop sensor known as an APS-H sensor. It was exclusively reserved for the 1D lineup until Canon introduced the 1D-X, at which point the APS-H sensor disappeared from production.
Figure 1.5 This image represents what you would capture using the three different-sized Canon sensors. The red stroke represents a ull-frame shot made at 17mm. When using the same lens, and APS-H sensor (purple stroke) captures a bit-tighter shot because of its 1.3x crop. Even tighter is the APS-C sensor’s crop (green stroke), offering a roughly 32mm perspective.
The size difference for crop sensors is determined by the sensor’s crop factor. This is where the sensor matters when it comes to lenses. A Canon APS-C crop sensor has a crop factor of 1.6x (the now-discontinued APS-H has a 1.3x crop factor). The larger the crop factor, the smaller the sensor. For the crop factor to become relevant in this case, you must multiply the focal length of the lens by 1.6 to determine the actual focal perspective in which you are shooting. Sounds confusing, and it is unless you see it for yourself!
Let’s say you are using a 50mm focal length on both a full-frame camera, such as the Canon 6D, and on an APS-C crop-sensor camera, such as the Canon 70D. For the full-frame camera, which has a crop factor of 1x, the perspective provided when looking through and shooting with the 50mm focal length is actually 50mm. However, for the 70D, we must multiply the focal length, 50mm, by the crop factor, 1.6, to determine the visual perspective with which we’re shooting: 80mm. Since the crop sensor chops a considerable amount of sensor away from a full-frame chip’s perimeter, the area of the lens now used can be equated to an 80mm lens on a full-frame sensor. If you are using a crop-sensor camera, multiply any focal length by 1.6 (or 1.3 if you have an APS-H camera), and you’ll find out what the equivalent perspective is on a full-frame camera.
A crop sensor does not actually magnify the focal length of any lens. It simply crops the sides, top, and bottom of the lens’s angle of view. However, crop-sensor cameras are a big hit with folks in the sports and wildlife photography arenas, because compared to a full-frame camera that packs the same resolution (megapixels) as a crop-sensor camera, the crop sensor provides a bit further “reach” when looking at two images of the same size. This is not magnification, just simply the result of two different-sized sensors of the same resolution being combined with the same focal length.
Putting Them in Perspective
So, practically speaking, how does this affect you? It really all depends on which camera you are using. If you are shooting with a full-frame Canon camera, the focal length of the lens with which you are shooting is going to result in that true perspective. However, on a crop-sensor camera, the perspective you get when putting any lens on the camera is simply not as “wide” as it would be on the former type of camera. There is nothing wrong with a crop-sensor camera. They are more affordable because of manufacturing costs, and many are built with the same structural quality as their full-frame versions. However, the next time you read online that an ultra-wide image was shot with a Canon EF 16–35mm f/2.8L on a Canon 5D Mark III, you might consider looking into a Canon EF-S 10–22mm f/3.5–4.5 for your Canon Rebel T5i. At 10mm with this latter combo, you are actually achieving the 16mm perspective of the former’s image.
Wait, we’re not done with this subject yet! To make it even more complicated, Canon makes a set of lenses that work exclusively with their APS-C crop-sensor cameras. Whereas all EF-marked lenses work on both full-frame and crop-sensor cameras, EF-S lenses only work on crop-sensor cameras. The EF-S lenses are fewer in number, but Canon tries to accommodate crop-sensor camera owners by offering equivalents to some of the most popular EF lenses (such as the previous example). Typically, EF-S lenses are more affordable than their EF counterparts, but if you are thinking about upgrading your camera body from a crop-sensor to full-frame sensor unit, you might hold out for EF glass instead of purchasing a lens that might be useless in the near future. This is one of the deficiencies of moving to a full-frame sensor camera system: Some, if not all, lenses might also need to be updated (or upgraded) to fit the new camera. Usually, photographers see this as a valuable transition from one system to the other, but it does come at a premium.