Originally posted by unfocused A typical well-spec'ed, last-of-the-film-era full-frame SLR body, such as my Contax Aria, weighs 460g and measures 137x92x54. Nice feel, comfortable weight and a pleasant companion all day long. Many people must be wondering: why, in simple language please, does FF digital (or even APS-C) need to be bigger and more burdensome than this?
Simply put: electronics.
Rear and top LCD's, control wheels, and individual, tactile switches all demand additional physical space.
SR takes up a lot of space internally as does all the electronics supporting the sensor. You have a small computer tied to the sensor. This computing circuitry takes up much more space than a roll of film spooled at both ends did.
Also, the sensor is a very delicate instrument requiring substantial bracing and damping integrated into the body of the camera. Film needed a pressure plate and did not require isolation from static electricity like a sensor does.
Larger sensors and/or more megapixels, and high frame rates, not to mention video demand larger, faster autofocus systems, both the added sensors and the motors. the data dumps add size and more channels to the
There are SD cards and HDMI and USB and IR and soon WiFi. There's a flash.
Above all is the requirement for power. bigger, faster sensors and their data dumps and processing require a lot of battery juice, and that takes up considerable space.
Once you have the lens mount, mirror, prism, finder, and shutter you pretty much have an SLR. The form factor cannot get much smaller than an ME Super. If you want/need to add any/all of the above, especially autofocus systems and all the feedback apparatus like LCD's, you're locked into a much larger body. The electronics can only be miniaturized so far before heat becomes a problem, or it is far too costly in materials and other compromises to get there.
If you want to do without autofocus and want small lenses there is Leica's M9 and all its rangefinder compromises, not the least being price.
If you want smaller bodies you need to start with a smaller sensor. Canon S100, Pentax Q, Panasonic LX5, Nikon V/J1 are your choices. Some bridge cameras may do as well. NEX-7 speaks volumes.
If you are looking for all those electronics to get shimmed into a *ist package alongside a larger sensor you will do without features in a larger, comparable Nikon or Canon, for the same price.
So far, the history of camera sales, recent and past, does not favour compactness at the expense of features. People will unhesitatingly buy a larger camera to get features. They will also buy a second camera with IQ compromises to get their portability. Camera makers love that idea: one customer, 2 cameras.