Digital SLR cameras sensor sizes

I have recently had to answer questions from a friend wishing to purchase his first digital slr camera and his first lens. With his questions, I realised how the current range of digital SLRs, sensor sizes and lenses could be confusing to a beginner. Here is what can be explained.

The reason of those different sensor sizes

The design digital SLR cameras is very similar to the pre-existing analog cameras. The difference is that the image is no longer captured on film. The film casing is replaced with the sensor mount, internal memory and memory card compartment. These cameras also have more efficient batteries because the sensor and electronics consome more energy than in their analog counterparts.

But the size of the image capture area can also be different. Whereas analog cameras always captured images on the same surface of film (24 by 36 mm), digital SLR camera sensors are not all of that size. The smaller the sensor is, the easier it is to manufacture. 24x36 mm sensors are still an exception present only on a handful of Canon cameras.

Relative sensor size comparison

Large sensors

APSC Sized sensors

4/3 and point and shoot sensors