Ask pretty much any digital photographer what "full frame" is and they'll tell you it's sensor based on a full 35mm frame's dimensions, which measures 24x36mm. Back in the heyday of film, there were fewer options... Especially when the 35mm format came about 101+ years ago in 1913 - though it wasn't really popularized until a dozen years later, in 1925 when Oskar Barnack used this format for his Ur Leica. But in today's digital cameras it seems like there are countless variations of sensors sizes (e.g. APS-C, APS-H, m4/3, etc.).
So what is it about full frame(link is external) that fascinates so many shooters? Does the sensor size really matter? Who cares if the sensor is smaller, if it has more megapixels in resolution? Surely that means it's better. Well, yes and no. In this article we'll take a look at some of the considerations of sensor size and why full frame seems to be the Holy Grail of digital photography. It's not meant to be a lengthy, in-depth explanation. Quite frankly, it's just not that exciting.
Full Frame Sensors
It's important to point out that full frame has, until recently, been solely the realm of DSLRs. Why is that? For the most part, camera body size and the fact that most lenses on the market at the beginning of digital photography were designed for 35mm film cameras. You needed a camera that was large enough to hold such a sensor (which is physically larger) and more importantly, work with the existing lenses. Lenses designed for 35mm SLRs have particular dimensions that demand a larger body - because of the flange focal distance(link is external) (the depth from the lens mount to the film/sensor plane). SLRs required this extra depth because of the mirror, and lenses had to stay clear of it. As a point of contrast, the Leica M rangefinder lacks a mirror (relying on the optical rangefinder instead) which makes the overall camera depth much thinner. Of course, this presented a unique conundrum for Leica which we'll get into below.