Camera Sensors Explained
What’s full frame? What’s APS-C? Not all camera sensors are the same, so understanding what a camera sensor is and how it functions will give you a better sense of your camera’s capabilities. In this guide, we’ll break it down to get you set up for success. Let’s get started.
What Is a Camera Sensor?
A camera sensor is made up of millions of tiny microlenses, RGB filters, microscopic metal wiring, and photosites, which are layered. Today, most camera sensors use CMOS (Complementary Metal-Oxide-Semiconductor) technology. The four common types nowadays are standard CMOS, stacked, BSI (backside illuminated), and global shutter.
When you press the shutter button on a camera with a CMOS sensor, it begins to capture and record the light passing through your lens. After going through RGB filters, photosites convert the photons coming though into an electrical signal.
That electrical signal is then sent to an analog-to-digital converter (A/D or ADC) that converts the electrical signal into pixels (picture elements). The pixels go through a digital processor, ultimately resulting in an image.
How Other CMOS Sensors Work
Other camera sensors use different layering methods. The main alternative to standard CMOS sensors is BSI CMOS, stacked and partially stacked CMOS, and global shutter sensors.
- BSI CMOS sensors capture more light and a crisper image because the metal wiring is layered behind the photosites.
- Stacked sensors eliminate metal wiring, replacing it with additional memory and circuitry that reside behind the photosites. This results in fast readout speeds, which eliminate blackout when shooting. This is particularly useful when shooting in bursts.
- Partially stacked sensors use the same memory and circuitry as fully stacked sensors, but these components only cover part of the sensor.
- Unlike CMOS sensors which record images line by line, global shutters capture the entire image simultaneously, resulting in minimal latency between the top and bottom of the frame. These are commonly used in cameras designed for fast motion capture.
Camera Sensor Sizes
Not all cameras capture the same image because it depends on the sensor size. Some of the most common sensor sizes on the market include full frame, APS-C, Micro Four Thirds, and 1″.
- Phone camera sensors vary in size, ranging from 1/1.15″ to 1/1.3″, depending on the manufacturer, model, and year.
Full Frame vs. Crop Sensor
Full-frame sensors shoot in 35mm and have a surface area of 36mm x 24mm. They have a large field of view (FOV) and are physically larger than crop sensors. Crop sensors are smaller and, as the name suggests, have a cropped field of view.
- Digital camera manufacturers use 35mm as the industry standard because it was the most common width of camera film.
- There are different sizes of crop sensors. For example, point-and-shoot cameras can have a sensor size of 1/2.3″ or 1″, but mirrorless cameras can haveAPS-C sensors.
Crop Factor
A camera sensor’s crop factor is the ratio compared to 35mm. The crop factor determines the equivalent magnification between different sensor sizes. Full-frame camera sensors are 35mm, so the ratio is 1x. APS-C is a smaller sensor size and has a crop factor of 1.5x (1.6x for Canon cameras).
For example, a 50mm lens on a camera with a full-frame sensor has a 50mm focal length. On cameras with an APS-C sensor, a 50mm lens on the camera is equivalent to using a 75mm (50 x 1.5) lens on a full-frame camera, or 80mm (50 x 1.6) on a Canon.
Here is the crop factor equivalence for the most common sizes of camera sensors:
- Full Frame: 1x
- APS-C: 1.5x (1.6x for Canon)
- Micro Four Thirds: 2x
- 1″: 2.7x
Aspect Ratio
NOTE: Aspect ratio is not the resolution or the physical size of the sensor!
A camera’s aspect ratio indicates the image width relative to its height, represented as two numbers separated by a colon (e.g., x:y). For example, if your image is 1080 x 720 pixels, then the aspect ratio is 3:2.
There are different aspect ratios depending on what camera you’re using. The most common aspect ratios with traditional digital cameras are 1:1, 3:2, 4:3, and 16:9/9:16 (cell phones). Some cameras have variable aspect ratios, which are most often used for video.
Megapixels & Sensor Size
Pixels are the smallest units of measurement in digital photography. As mentioned above, a pixel is the converted light absorbed by photosites, and there are millions of photosites on a sensor. Knowing this, one megapixel (1MP) is equivalent to one million pixels.
The total amount of megapixels does not necessarily equate to quality, however. It’s light sensitivity that matters. For example, 24MP on a full-frame sensor has more dynamic range than 24MP on an APS-C sensor because the pixels are inherently larger. This also means you can shoot at higher ISO levels before quality degrades.
Depending on your application, you may not be able to tell the difference between APS-C and full frame unless you “pixel peep” (zoom in to look for flaws) or print on large formats.
- The total number of megapixels indicates the resolution of your image. So, if the image resolution is 6000 x 4000, then it’s 24MP.
- Higher pixel counts equate to larger file sizes.
- More total photons and larger pixels mean there’s often better dynamic range since they are able to capture more light.
- Megapixels in some devices such as smartphones, drones, and action cameras are sometimes due to on-device upscaling. In this case, they multiply the count by four times.
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