Recently, I have noticed a fair number of people who are somewhat new to photography asking about the differences between full frame and APS-C sensor cameras. With all of the various camera manufacturers and choices on cameras, having a basic explanation of the differences between the two sensor sizes can be helpful. In this article, I explain what the difference between the sensors is and how it relates to the field of view. I also touch on size and weight differences between a full frame camera kit and an APS-C camera kit. This article does not cover every aspect of the differences, but was written to help with understanding of the basics.
Digital Camera Sensors: Full Frame and APS-C
Digital cameras use an electronic sensor to capture light. This sensor is the digital replacement for film. Sensor size plays a role in some aspects of a photograph. For DSLR and mirrorless cameras, the most common sensor sizes are referred to as Full Frame or APS-C. A full frame sensor is the same size as a 35mm film frame (36mm x 24mm). APS-C sensors are typically about 2/3 of the size of a full frame sensor, which is why they are also called crop sensors. The exact size of an APS-C sensor varies by manufacturer. Note that digital cameras can have larger sensors, such as in medium format cameras, or smaller sensors. In this article, the discussion will be kept to full frame and APS-C sensors.
Sensors are comprised of light-gathering pixels. The number of pixels on the sensor gives the megapixel (1 megapixel = 1 million pixels) count for the camera. For example, a Nikon D850 is a full frame 45 megapixel camera having 8,256 x 5,504 pixels. The ability of a sensor to gather light is affected by both the sensor size and the pixel size. In general, larger sensors and larger pixels each contribute to higher-quality images. However, over time, advances in sensor technology improve so that current sensors with smaller pixels can capture light better than older sensors having larger pixels. For the purpose of this discussion comparing full frame and APS-C sensors, we will assume that the ability of pixels to capture light will be the same for the two sensor sizes. In this way, the primary differences between the two sensor sizes will be described without getting into the weeds on the nuances of various sensor differences.
Field of View and Effective Focal Length
For a particular focal length, a camera with a full frame sensor will capture a larger portion of a scene than a camera with an APS-C sensor. This is the reason why the APS-C sensors are also called crop sensors. They are smaller than full frame sensors and capture only a portion of what the full frame sensor captures. For this reason, marketing for APS-C cameras often refer to an effective focal length that is longer than the true focal length. For example, for a 50mm focal length on a full frame camera, an APS-C camera will have a field of view that is equivalent to about a 75mm focal length. Keep in mind that what this really means is that relative to a full frame sensor, about 1/3 of the image has been eliminated simply because the APS-C sensor is smaller. The greater effective focal length does not give greater magnification or resolution, it just gives a smaller area of the scene. When viewing this smaller area, it appears as if the image was shot using a longer focal length based on the smaller field of view. The image below compares the field of view for a full frame and APS-C camera shown against the image circle provided by a lens designed for a full frame camera. An image circle is simply the circular field of light that passes through a lens and strikes the camera sensor.
To obtain the same field of view with an APS-C camera as can be captured with a full frame camera, a shorter focal length would be required. For example, the field of view obtained by using a 50mm lens on a full frame camera could be approximately achieved by using a 35mm lens on an APS-C. The field of view with a 35mm focal length on an APS-C camera would not be exactly the same as 50mm on a full frame camera, but would be close.
When shooting close-ups or macro, a full frame camera will allow for more of the subject to fill the frame at a given distance from the lens. Depending on the subject size, lens focal length, and minimum focus distance of the lens, a full frame camera may be able to get closer to the subject without having part of the subject being out of the field of view.
Camera Kit Size and Weight
A major factor in selecting an APS-C camera is often the smaller size and weight of the camera and lenses. Many people look to reduce or minimize the overall bulk and weight of their photography kit. Cameras with APS-C sensors are typically smaller than those with full frame sensors. This size relationship holds true for both DSLR and mirrorless cameras. APS-C sensor cameras can use a smaller image circle which means that lenses can be smaller and lighter than those made for full frame cameras. Tripods, brackets, and other support equipment do not have to support as much weight as a full frame kit either. Therefore, the support equipment can also be lighter. A lighter and smaller APS-C camera kit can make an enormous difference when traveling or carrying gear around all day.
Lenses for full frame cameras must have an image circle that is larger than what is required for a camera having an APS-C sensor. Lenses made specifically for APS-C cameras generally cannot be used on full frame cameras because the image circle will not cover the entire sensor. On the other hand, lenses designed for full frame cameras can be used on both full frame and APS-C cameras.
Weighing the Pros and Cons of Full Frame vs APS-C
When deciding on a camera system that is right for you, weighing the pros and cons of full frame vs. APS-C sensor cameras is one of several factors that can be considered. The primary differences that have been focused on in this article can be summarized as follows:
APS-C (crop) sensor cameras tend to be smaller and weigh less. They are easier to carry around all day and to pack extra lenses if needed. Traveling with a APS-C camera kit is easier than with a full frame DSLR kit. Because they are relatively light, tripods and ball heads can use a lower weight capacity than full frame camera systems. While APS-C cameras do have a smaller field of view than full frame cameras, many people do not find them limiting at all. They are fully capable of producing very high-quality images.
Full frame sensor cameras are bulkier and kits tend to be heavier. However, they provide more flexibility in composition and more latitude for cropping. A full frame camera makes full use of the field of view of lens, which can be important for wide-angle shooting. In addition, the lens can get closer for macro/close-up photography and retain more of the subject in the field of view.