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?

I felt misled when I first learned that. The naming mixes the legacy of 1950s video tubes, the last years of 90s film, and the marketing of smaller, more capable cameras. Here’s how those histories ended up in the sensor names we use today.

① Medium Format

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

• Origin: In the film era, 120/220 roll-film formats were larger than 35mm but smaller than 4×5 inch “Large Format” sheets. That position between the two gave rise to “Medium Format.”
• 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:Kodak, Canon, Nikon, Fuji, and Minolta introduced this film system in 1996 as an alternative to 35mm film. The proposal combined easier loading with digital information recorded on the film, offering a more convenient photographic system. Its timing was unfortunate: digital cameras spread so quickly that the film format lost its place before it could become the replacement its makers had intended. The name nevertheless survived. In digital photography, it refers to sensor formats that follow the dimensions associated with that earlier film system, rather than to a continuing everyday film 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 looking at the “1-inch” class used in compact cameras, there’s an important naming distinction:

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

The name comes from video-camera tubes, whose outside diameter was larger than the usable imaging area. A tube measuring 1 inch across had an effective image area of only about 2/3 of an inch, approximately 16mm. The 1-inch name survived the switch to digital. A “1-inch” sensor therefore measures about 2/3 of an inch diagonally.

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

What is the difference?

• Origin: Both systems use the same sensor size. The distinction is the flange distance and the overall size of the system.
  • Four Thirds (FT): The DSLR standard needs space for a mirror, leaving a longer distance between the sensor and lens.
  • Micro Four Thirds (MFT): The mirrorless standard removes that mirror, bringing the lens closer to the sensor and allowing a smaller 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: It doesn’t physically measure 1 inch. “1-inch type” is the more precise name; calling it a “1-inch sensor” can give the wrong impression of its 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 size is standard in premium smartphone main cameras. Compared with older compact-camera sensors, they offer much stronger low-light results with the help of 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.

A 50mm lens is often described as standard because the corresponding view is considered close to human vision. That description assumes a reference format. Put the same 50mm lens on a crop-sensor or MFT camera and the picture covers a narrower part of the scene, which can be surprising if the label led you to expect a standard view. The lens’s physical focal length hasn’t changed. What changes is how much of its image circle reaches the recorded picture: the smaller sensor keeps the central section. The result looks as though a longer lens had drawn the scene closer. A crop factor expresses that relationship against the full-frame reference, giving the equivalent focal length used for comparison. That reference is why a focal-length description needs the sensor format alongside it.

I’ll explore focal length in more detail in a future post.

Optical/Mechanical Trends by Sensor Size

A 1-inch sensor doesn’t actually have a 25.4mm diagonal. If that feels misleading, I had the same reaction. The terminology survived several transitions, from film to digital and from tubes to semiconductors. I wanted to explain it because the physical size of “1-inch” cameras still seems to cause confusion.