- "Full Frame", so called because 35mm film is the "standard" of comparison of all Frame Sizes. There are still relatively few cameras on the market that are Full Frame - that is, their image is captured on a 36X24mm Frame being exactly the same size as that of 35mm film. Canon was the first DSLR to offer Full Frame, in it's EOS 5D, and they have simply kept improving the 5D through upgrading it through "Mark II" and "Mark III" models. Nikon has been less conservative, offering Full Frame on its D1 through D4 Model range (very large professional bodied cameras), and with the D700 and D800 "consumer-sized" bodies. Finally, there is Leica, the extremely elitist and expensive German made cameras that are in fact not DSLR's at all, maintaining the classic and very compact Rangefinder body design, true to their tradition that goes way back to the 1920's Their current M9 Digital Rangefinder body has a Full Frame Digital Sensor. So this is the complete roster of Full Frame Digital Cameras that are available today.
- APS-H, so called because it is based on a short-lived film frame standard of 27X18mm called "Advanced Photo System". This one is a real orphan, and only the Canon EOS 1D Series uses it.
- APS-C, also based on an Advanced Photo System film frame of 24X16mm. By far, most DSLR's made today by Canon, Nikon, Pentax, Sony and Sigma use the APS-C sized sensor, with very small variations in the actual dimension.
- "Four-Thirds" and "Micro Four-Thirds" together are fast catching up to APS-C sensors. Originally used in Olympus DSLR's, this new frame standard which measures closer to half the Full Frame size at 20X15mm is also a little different, because the dimension ratio of 35mm and APS Film is 3:2, the Olympus standard is 4:3, hence the name. The difference between Four-Thirds and Micro Four-Thirds is that the latter is popular on the newest trend of "Mirrorless Interchangeable Lens Cameras" (MILC's) being sold by Olympus and Panasonic mainly.
However, the most profound effect that different sensor sizes (frame sizes) have in the real world is directly related to "lens size". If you're a DSLR owner, you already know all this stuff - so I'm providing this simplified explanation to people who are new to it.
Quite simply, the smaller the sensor, or frame, the smaller will be the lens required to fill the frame, both in the lens' diameter and its focal length. With fixed lens Compact Cameras, with frame sizes as small as 6mm, the lens can be about 1/6 the diameter and length of the lenses used for 35mm film, or "Full Frame" Digital Cameras. This is why you can cram a zoom lens that goes to a 300mm Telephoto Focal Length into a camera where that lens collapses completely and the whole thing can be carried in your pocket, but users of DSLR and film SLR Cameras still need to walk around with a heavy camera and a lens over 8 inches long hung around their necks to achieve the very same Zoom. It all comes down to the precision of miniaturization that has been accomplished with Digital Cameras.
To the Compact Camera owner, this doesn't matter in the slightest. They cannot interchange the lenses on their cameras, and the one lens that the camera is built with can cover the range from a 24mm Wide Angle, all the way to 300mm Telephoto, and the camera is still small enough to fit in a pocket. This is because the sensor is approximately 1/6 the size of "Full Frame", and reality, the lens is about 1/6 of the Focal Length of conventional 35mm lenses, so the actual focal length range of these miniaturized Compact Zoom Lenses is 4mm through to 50mm, to provide an equivalent 24 - 300mm Optical Zoom.
The Frame Size difference becomes more apparent to DSLR users however. If you own one of the relatively rare and expensive Nikon, Canon or Leica "Full Frame" cameras listed above, then all those 35mm film SLR lenses you've collected over the last 40 years will work on your new camera in exactly the same way they did on your old Canon, Nikon or Leica film cameras. Things get different only if you own one of the far more common Canon or Nikon APS-C sized DSLR's however. Technically speaking, all of your old lenses will still fit on your new DSLR's mount, but now the APS-C sensor is smaller than the lens was designed for. So in a sense, you still don't care because the lens mounting standard for each brand of camera, including the electronic contacts between the lens and the camera, have not changed, which is why a 30 year old lens from a Film SLR will still function fully and perfectly on a new DSLR. But there is a difference between the mount design and the lens's optical behaviour if you have an APS-C (not a full frame) sized camera. Because the lens is a bit larger than the frame, this means that the frame is "cropping out" a lot of the picture that extends beyond the rectangle in the middle which represents the APS-C sized frame. You don't really "see" this happening with your eye, because your camera's optics reflect the image through this very same lens up to the Viewfinder, so it's still "business as usual". Except for one thing. If you put an old 50mm film SLR lens on a new APS-C sized DSLR, everything will appear closer by comparison. This is because the smaller sensor is cropping off a lot of the image, exactly the same way you would do with Photoshop, to crop parts of the picture outside of the center that don't matter - now the camera is doing that for you, and there's nothing you can do about it. To get the same amount of scenery into the smaller frame with your old 50mm lens, you will need to step back a considerable distance if you use that lens on a APS-C sided DSLR. Another way of putting it is that your "normal" 50mm lens has now become a "moderate telephoto" equivalent to a 75mm (or Nikon) or 80mm (for Canon) lens.
The camera makers have gotten around this by providing new "digital lens" specifications, especially with Zoom lenses. So that when an old Canon Film SLR would have been sold with a 28-80 "Kit Zoom", the new standard for Digital SLR's is the 18-55 "Kit Zoom" - a smaller and lighter lens that covers exactly the same zoom range.
So to conclude - does size matter? The answer is, of course yes and no. Yes, because the bigger the frame, the bigger each individual Pixel can be, with corresponding increases in light sensitivity and picture quality. No, because the bigger the frame, the bigger and heavier your camera and lens have to be, and if you are usually shooting in normal lighting, or you don't object to using the built in flash a lot, the Compact Cameras where everything is about 1/6 of the scale of a Full Frame DSLR have a lot to offer, with respectable, usable picture quality, and light sensitivity that's about the same as the good old ASA400 Kodacolor Film used to be.
The advantages of owning a DSLR are few, but significant. They provide:
- Ultimate picture quality, especially if you can afford a Full Frame model
- You can use your old Film SLR lenses
- Ultimate light sensitivity - with ISO's as high as 12,800 (compared to the old film days of 400, and also to get a reasonable quality from a Compact Digital), you can now get away with taking pictures at night without a tripod.
- Greater creativity, and more built in features
- Real Optical Viewfinders