Camera Sensor Sizes Explained: Why 1-Inch Isn’t Really 1-Inch

Excerpt from camera brand marketing pages and spec sheets.

Did you know that a camera’s “1-inch” sensor isn’t actually one inch?

When I first learned this, I felt truly betrayed. This confusion is the result of a tangled history: the remnants of 1950s vacuum tube technology, the final gasps of 90s film, and the marketing need to claim hardware was “smaller yet better.” Today, let’s clear up the mystery behind camera image sensors.

① Medium Format

Why is it called “Medium” and not “Large”?

• Origin: During the film era, sensors larger than 35mm but smaller than the massive 4×5 inch “Large Format” films were categorized as 120/220 roll film, leading to the “Medium” designation.
• Size: Approximately 2.1 to 2.7 inches diagonally (typically 44x33mm or 53x40mm).
• Characteristics: The large surface area provides superior dynamic range and image quality, serving as the pinnacle of commercial photography.
• Examples: Fujifilm GFX 100II, Hasselblad X2D 100C.

② Full Frame (35mm)

The gold standard for conversion.

• Origin: Based on the 36x24mm frame of 35mm motion picture film, which was the standard for over 100 years.
• Size: Approximately 1.70 inches (43.2mm) diagonally. The “35mm” term refers to the physical width of the film strip.
• Characteristics: It has a crop factor of 1.0, making it the global standard for lens design and focal length calculations.
• Examples: Sony A7M4, Canon EOS R5 Mark II, Nikon Z8.

③ APS (Advanced Photo System)

The ill-fated film trio.

• Origin: Introduced in 1996 by Kodak, Canon, Nikon, Fuji, and Minolta to replace 35mm film. While it promised digital convenience, it was quickly eclipsed by the rapid rise of digital cameras. Today, the name persists as a sensor size standard.
• Size: Digital APS typically refers to C, though H existed in older models.
  • APS-H (High Definition): 30.2 x 16.7mm (16:9 ratio). Used in early digital cameras like the Canon 1D series.
  • APS-C (Classic): 25.1 x 16.7mm (3:2 ratio). The ancestor of the modern “crop sensor.” It was designed to be slightly smaller than physical film.
  • APS-P (Panoramic): 30.2 x 9.5mm (3:1 ratio). Designed for panoramic shots, it did not transition to digital.
• Examples: Fujifilm XT5, Sony A6700, Canon EOS R7.

(Important!) Video Camera Tubes (Vidicon) and Sensor Size

Before we dive into the “1-inch” sensors found in compact cameras, there is one crucial fact to address:

It is technically not a 1-inch image sensor, but a “1-inch Type” sensor.

In digital cameras, a 1-inch sensor is actually much smaller. This is a legacy from the vacuum tube video camera era. When the external glass tube diameter was 1 inch, the effective imaging area was only about 2/3 of an inch (approx. 16mm). The industry kept this naming convention even in the digital age. So, a “1-inch” sensor is actually about 2/3 of an inch diagonally!

④ Four Thirds (FT) vs. Micro Four Thirds (MFT)

What is the difference?

• Origin: Many people are confused, but the sensor size is the same. The difference lies in the flange distance and system size.
  • Four Thirds (FT): A DSLR-era standard. Because of the mirror, the flange distance (space between the sensor and lens) is long.
  • Micro Four Thirds (MFT): A mirrorless standard. By removing the mirror, the lens can be placed closer to the sensor, significantly shrinking the entire system.
• Size: Based on the aforementioned 4/3-inch vacuum tube standard (approx. 0.85 inches diagonally), with a 4:3 aspect ratio.
• Examples: Panasonic Lumix GH7, OM System OM1.

⑤ 1-inch Type

The accurate terminology.

• Origin: Follows the effective area of a 1-inch external diameter Vidicon vacuum tube.
• Size: Approximately 0.63 inches (15.8mm).
• Warning: Because the physical size is not 1 inch, it is technically correct to call it a “1-inch type.” Calling it a “1-inch sensor” can lead to misconceptions about its physical dimensions.
• Examples: DJI Osmo Action 6, Sony ZV1 II, Xiaomi 17 Ultra.

⑥ Sub-inch Sensors

• Most flagship smartphones use 1/1.3-inch type sensors.
• This is the standard for modern premium smartphone main cameras. They have surpassed old-school point-and-shoot sensors and now deliver incredible low-light performance thanks to powerful AI processing.

Why does my 50mm lens look like a telephoto?

Even if you use the same 50mm lens, the angle of view changes depending on the sensor size.

In photography, 50mm is often called a “standard lens” because it mimics human vision. However, if you attach a 50mm lens to a crop-body or MFT camera, you might be surprised to see the field of view is much narrower. This is because the focal length printed on a lens is a physical constant, but the actual field of view depends on the sensor size. Smaller sensors “crop” the center of the image circle, making the resulting image look as if you used a telephoto lens. We use a “crop factor” to calculate this “equivalent focal length.”

We will dive deeper into the physics of focal lengths in a future post!

Optical/Mechanical Trends by Sensor Size

Now you know that a 1-inch sensor is not actually 25.4mm wide. I’m not the only one who felt betrayed, right? It’s just a byproduct of the transition from film to digital, and from vacuum tubes to semiconductors. I wrote this because there seems to be some lingering confusion regarding the physical size of “1-inch” cameras.