3. 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 the current Nikon camera models, such as the DF, D610, D750, D810, and the D4S, and all of the older D4, D600, D700, D800/E, and D3, D3S, and D3X models. Nikon uses the designation FX for all of the full-frame sensor cameras. For those photographers moving from film SLR 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. For many, particularly portrait photographers, landscape photographers, and photojournalists, a full-frame sensor is much desired for many reasons beyond how it correlates with the use of our lenses.
A crop sensor shares the same rectangular perspective (often referred to as the 3:2 ratio) but is considerably smaller. How much smaller? For Nikon crop-sensor, or DX, cameras, a bit more than 50 percent smaller. At the time of writing, Nikon makes only one size of crop sensor, which measures approximately 24mm by 16mm (Figure 1.7). These sensors can be found in all the current DX cameras—the D3300, D5300, and D7100.
Figure 1.7 This image represents what you would capture using the two different-sized Nikon sensors. The red stroke represents a full-frame (FX) shot made at 17mm. With the same lens, the smaller DX sensor captures a tighter shot (outlined in green) because of its 1.5x crop.
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 Nikon DX crop sensor has a crop factor of 1.5x. 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 1.5 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 (FX) camera, such as the Nikon D810, and on an crop-sensor camera (DX), such as the Nikon 7100. 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 D7100, we must multiply the focal length, 50mm, by the crop factor, 1.5, to determine the visual perspective with which we’re shooting: 75mm. 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 75mm lens on a full-frame sensor. If you are using a crop-sensor camera, multiply any focal length by 1.5 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 Nikon 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 an AF-S Nikkor 16–35mm f/4G ED VR on a Nikon D810, you might consider looking into an AF-S DX Nikkor 10–24mm f/3.5–4.5G ED for your Nikon D5300. 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, Nikon makes a set of lenses designed to work with their DX crop-sensor cameras. Whereas all the Nikon lenses work on both full-frame and crop-sensor cameras, the lenses labeled DX were designed for the DX camera’s smaller sensor. When a DX lens is used on an FX body, the camera automatically crops the image, effectively turning the full-frame body into a cropped-sensor body. The DX lenses are fewer in number, but Nikon tries to accommodate crop-sensor camera owners by offering equivalents to some of the most popular lenses. Typically, DX lenses are more affordable than their full-frame 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 full-frame glass instead of purchasing a lens that might be limiting in the near future. This is one of the issues 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.