Four Thirds system
The Four Thirds system uses a 4:3 inch-based image ratio, as with other compact digital cameras as opposed to a full-frame digital SLR, which usually uses the 3:2 ratio of the traditional 35 mm format. The actual size of the Four Thirds sensor is however much smaller: 18 mm x 13.5 mm. This is about 40% less than sensors used in most digital SLR, but almost 10 times larger than sensors typically used in compact digital cameras.
A Micro Four Thirds camera is a cross between a standard point-and-shoot camera and a digital SLR. The difference between a point-and-shoot camera and an MTF camera is that MFTs have small interchangeable lenses and good size sensors. The difference between a digital SLR camera and an MFT camera is that MFTs do not have a mirror and viewfinder. A shot is composed only on the LCD screen. This technology provides much smaller cameras than SLRs, while still producing excellent images.
Bridge cameras fill the gap between digital compact cameras and digital SLRs by offering the technology found in both. They are more compact than SLRs but certainly not pocket size and also more restricted in terms of lens options and the range of features. Bridge camera lenses are fixed, but usually have a very large zoom range and are also normally able to tackle reasonable macro images. Although they offer the facility of point-and-shoot, they also have a good range of exposure modes, metering options, special programmes, good size LCD screens etc. and offer full manual control. Although megapixels are often in double figures, image quality will not compare to digital SLRs as the image sensors are smaller.