If we compare a typical sensor size to a 35 mm film, we realize that the sensor size of digital SLRs is typically 40% to 100% of the surface of the 35 mm film. Although they have similar number of pixels, digital cameras have smaller sensors. As a result, the pixels are smaller and the image quality is different in terms of noise and dynamic range.
Sensor Type Designation
If we talk about sensors, we refer to 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 is similar to a set of standard sizes, given to TV camera tubes in the 50’s. The size designation defines the outer diameter of the long glass envelope of the tube and not the diagonal of the sensor are. It has been proven that the usable area of this imaging plane is approximately two thirds of the designated size. Although it is always roughly two thirds, there is no specific mathematical relationship between the diameter of the imaging circle and the sensors size.