What is a four-thirds sensor? Is a 35mm sensor measured across the diagonal (like a TV screen) or width etc.? What is ASPC?
The answers I found are:
- http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm
- Sensors are often referred to with a “type” designation using imperial fractions such as 1/1.8″ or 2/3″ which are larger than the actual sensor diameters. The type designation harks back to a set of standard sizes given to TV camera tubes in the 50’s. These sizes were typically 1/2″, 2/3″ etc. The size designation does not define the diagonal of the sensor area but rather the outer diameter of the long glass envelope of the tube.
- There appears to be no specific mathematical relationship between the diameter of the imaging circle and the sensor size, although it is always roughly two thirds.
- {The article includes a look-up table for the exact figures}
- A “35” mm sensor is actually 36 mm on the width; the height being 24 mm and the diagonal 43 mm.
- http://en.wikipedia.org/wiki/APS-C
- Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System “classic” size negatives. These negatives were 25.1 × 16.7 mm and had an aspect ratio 3:2.
- Sensors meeting these approximate dimensions are used in many digital single-lens reflex cameras, in addition to a few large-sensored live-preview digital cameras and a few digital rangefinders.
- Such sensors exist in many different variants depending on the manufacturer and camera model. All APS-C variants are considerably smaller than 35 mm standard film which measures 36×24 mm. Sensor sizes range from 20.7×13.8 mm to 28.7×19.1 mm. Each variant results in a slightly different angle of view from lenses at the same focal length and overall a much narrower angle of view compared to 35 mm film.
- This is why each manufacturer offers a range of lenses designed for its format.
- http://philipbloom.net/2009/10/01/5dmkii-or-the-7d/
- Philip includes a diagram comparing sensor sizes.