In digital cameras, full frame sensors are sensors that measure 36mm x 24mm.
The size is based on 35mm film cameras. But how?
I hope this diagram makes it clear. The top to bottom height of 35mm film is 35mm. That’s the standard, and it has been the standard for over a century.
But the film has to move along so that with each wind-on of the film advance, a new frame is in front of the lens ready to be exposed.
The manufacturers stamp sprocket holes at regular intervals along the film. The film advance sprockets catch in those holes and move the film along.
If the image that the lens casts onto the film covered all the 35mm depth of the film, then the finished photographs that we look at would have holes at regular intervals across them, corresponding to the sprocket holes.
So the camera manufacturers put a frame in front of the film to mask off any light that might fall beyond the rectangle. And the size of the frame is a rectangle that’s 36mm x 24mm.
And that’s why ‘full frame’ digital sensors are 36mm x 24mm
Not all digital sensors are full frame. Here are the relative sizes of some of them, from full frame down to the sensor found in the iPhone 15 Pro. There are bigger sensors than full frame but they are pretty uncommon.
