Understanding Camera Sensor Sizes
Medium format, full-frame, APS-C and Four Thirds are commonly used camera sensor sizes. This post explains their significance and the impact of sensor size on photography.
From left to right we have cameras with a Four Thirds type, APS-C format and full-frame sensor. Although the Micro Four Thirds Panasonic Lumix G9 II has the smallest sensor, it is as similar size to the full-frame Nikon Z7 II.
When film photography reigned supreme, 35mm film was the go-to format. You’d crack open a film canister, carefully load the film into your camera and be ready to shoot. Whether using a simple point-and-shoot or a professional-level SLR, the film size remained the same.
In digital cameras, film has been replaced by sensors and there are a variety of sizes in common use. By sensor size, I mean the physical size of the chip, not its pixel count or resolution.
A ‘full-frame’ sensor matches the size of a 35mm film frame at 24x36mm, sometimes dropping to around 23.9x35.9mm. There are also smaller sensors like APS-C, Four Thirds, 1-inch and even smaller formats. APS-C sensors are named after the short-lived Advanced Photo System Classic film format, which measured 25.1x16.7mm, however, APS-C sensors typically come in at about 23.5x15.6mm.
There are also sensors that are larger than full-frame format chips. Fujifilm, for instance, has the GFX line of medium-format cameras. These cameras, such as the Fujifilm GFX100S II, have a sensor that measures 43.8 x 32.9mm, close to 1.7x the size of a full-frame (35mm) sensor.
Another difference to note between Four Thirds and full-frame or APS-C format sensors is their aspect ratio. The Four Thirds sensors in Micro Four Thirds cameras have a 4:3 aspect ratio, while full-frame and APS-C format sensors have the same 3:2 aspect ratio as 35mm film.
Read our Fujifilm GFX100S II Review
The origins of names like Four Thirds, 1-inch, and 2/3-inch are rooted in the era of video camera tubes, which is why their naming conventions can seem a bit obscure. However, these names have stuck, and they represent a range of sensor sizes: Four Thirds sensors are usually around 17.3x13mm in size, 1-inch sensors are about 13.2x8.8mm and 2/3-inch sensors typically measure 8.6x6.6mm. As you might guess, Four Thirds sensors are found in modern Micro Four Thirds cameras.
Medium format sensors are named after medium format or 120 film, with typical film frames of 6x4.5cm, 6x6cm and 6x7cm. Interestingly, 35mm film was often called ‘small format’ to distinguish it from medium format film.
Sensor Dimensions
Here’s a list of the common sensor sizes and their typical dimensions:
1-inch sensors - 13.2x8.8mm
2/3-inch sensors - 8.6x6.6mm
Four Thirds (Micro Fours Thirds cameras) - 17.3x13mm
APS-C sensors - 23.5x15.6mm
Medium format - 43.8 x 32.9mm
What’s the Advantage of a Big Sensor?
The buzz around full-frame and medium format cameras stems largely from the size of the photosites (commonly known as pixels) on their larger sensors. Bigger pixels can capture more light, producing a stronger image signal. This stronger signal means less need for amplification, resulting in images with less noise, or grain, particularly in low-light situations. This is why cameras with larger sensors often offer higher ISO settings and better performance in challenging lighting conditions.
Having a larger sensor also allows more pixels to be squeezed onto a sensor without image quality being over-compromised. The medium format Fujifilm GFX100S II and GFX100 II, for example, have a resolution of 102MP.
This graphic shows the relative sizes of full-frame, APS-C with 1.5 crop, APS-C with 1.6x crop and Four Thirds type sensors. Click on the graphic to see an enlarged view.
Focal Length and Crop Factor
Although camera sensors are rectangular, lenses produce a circular image. This must completely cover the sensor so there are no blank areas in the image.
Sensor size also affects the lenses you need and how they behave. Larger sensors require lenses that produce larger image circles, which usually means bigger lenses. If you use a full-frame lens on an APS-C sensor camera, the lens’s image circle exceeds far beyond the sensor size and the image is captured from just a small section within the circle. This results in what appears to be a cropped image and the effect is often called the crop factor or focal length magnification factor. It makes the lens appear as if it has a longer focal length on a smaller sensor. The smaller the sensor, the greater the crop factor.
This graphic shows the relative sizes of the different sensors and the image circles that are required to cover them. Click on the graphic to see an enlarged view.
For example, Fujifilm, Nikon, and Sony APS-C cameras have a crop factor of 1.5x, so an 18-55mm lens gives a field of view equivalent to a 27-82.5mm lens on a full-frame model. Meanwhile, Canon’s APS-C cameras have a crop factor of about 1.6x, making the same lens appear like a 28.8-88mm lens on a full-frame camera.
Micro Four Thirds cameras have a 2x crop factor so they double the effective focal length of lenses. Consequently, a 14-42mm lens on a Micro Four Thirds camera behaves like a 28-84mm lens on a full-frame camera. This is especially interesting with longer lenses, as a 300mm lens effectively becomes a 600mm lens.
Superzoom and bridge cameras typically have very mall sensors and this enables them to achieve vast effective focal length ranges and long zooms on compact bodies.
This image was photographed on a full-frame camera at a focal length of 35mm.
This image was photographed on a full-frame camera at a focal length of 70mm. The trees appear closer, or larger, in the frame than in the image shot at 35mm.
Depth of Field: The Sensor and Lens Relationship
Larger sensors are often touted for their ability to produce shallower depth of field, which helps create those creamy, blurred backgrounds that make subjects pop. However, this is actually more about the relationship between sensor size, focal length and aperture. To achieve the same framing with a full-frame camera and an APS-C camera, you need to use different focal lengths. Because depth of field decreases as focal length increases, changing the focal length affects the depth of field.
For instance, if you’re shooting with a Nikon Z50 (an APS-C camera) and a 35mm lens, the 1.5x crop factor means the lens behaves like a 50mm (actually 52.5mm) optic would on a full-frame Nikon Z6 III. However, at any given aperture setting, a 35mm lens captures greater depth of field (a bigger in-focus area) than a 50mm lens. This means that you need a wider aperture on the 35mm with the Z50 to capture the same depth of field on the Z6 III with a 50mm lens.
How Does Sensor Size Impact Resolution?
A digital camera’s sensor is packed with millions of tiny light receptors known as pixels. When light hits the sensor, each pixel generates a signal based on the light’s intensity, which is then converted into a digital image. The number of pixels on a sensor determines the resolution of the images it produces, with more pixels generally allowing for larger prints and more detailed images.
Read our Guide to Camera Sensor Resolution
However, the number of pixels isn’t the only factor in image quality; sensor size plays a crucial role as well. A larger sensor with fewer, but larger, pixels can capture more light, resulting in stronger image signals and, consequently, better image quality. This is why full-frame sensors, despite sometimes having a similar number of pixels as smaller sensors, often produce superior images with less noise and greater dynamic range in low light.
These are both Micro Four Thirds cameras and have the same size sensor. Using a small sensor allows camera manfuacturers to make smaller cameras if they want.
What are the Advantages of Small Sensors?
While larger sensors offer advantages in terms of image quality, pixel count and depth of field control, they come with trade-offs. For a start, the sensor is typically the most expensive component in a camera, so opting for a full-frame model usually means a significant increase in cost. Full-frame lenses also need to produce a larger image circle, making them bulkier and more expensive than their APS-C or Micro Four Thirds counterparts. In some cases, there’s not a significant difference in the size of cameras with different-sized sensors, but the bulk and weight saving made with Micro Four Third and APS-C format lenses can be very significant.
Consequently, cameras with smaller sensors, like APS-C or Micro Four Thirds, are often more appealing to photographers seeking a compact and lightweight system. They can produce great image quality in a more portable package, making them ideal for travel, street photography, or any situation where space and weight are key considerations.
Thanks to their 2x focal length magnification and very acceptable image quality, OM Systems Micro Four Thirds cameras have proved very popular with wildlife photographers who need long telephoto lenses.
Choosing the Right Sensor Size
Ultimately, the right sensor size for you depends on your photographic needs and preferences. If you prioritise image quality, low-light performance, and shallow depth of field, a full-frame or medium format camera might be worth the investment. On the other hand, if portability, affordability and versatility are more important, an APS-C or Micro Four Thirds camera could be the better choice.
Each sensor size comes with its own set of advantages and disadvantages, so it’s important to consider what matters most to you in your photography. Whether you’re shooting sweeping landscapes, intimate portraits, or fast-paced action, understanding sensor size will help you make the best choice for your needs.
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