At the other end of the scale, the Sony A7 series uses full-frame sensors. Compact system cameras are now starting to rival digital SLRs in every area of the market, not just 'amateur' cameras.
Compact system camera types
Many makers are designing compact system cameras for photographers who want better image quality than they can get from a regular compact camera, but with the same automatic functions and ease of use and the ability to change lenses.
This means there is a good selection of low-cost compact system cameras, easy-to-use models aimed at novices and compact cameras small enough to slide into a jacket pocket or a small bag, and you can check our list of top mirrorless compact system cameras for beginners.
There are plenty of more advanced models too, aimed at photographers who already know the basics and want to step up to a camera that offers better quality and more photographic options and control than they can get from a compact camera.
Some of these mid-range mirrorless compact system cameras have electronic viewfinders, some don't. A few can accept clip-on viewfinders that connect to the camera electronically, though these have to be bought separately.
But compact system cameras are also starting to rival digital SLRs in a very direct sense, copying the D-SLR design with a viewfinder and 'pentaprism' shape on the top of the camera, but using an electronic viewfinder rather than the optical sort.
This type offers the look and feel of a digital SLR, but with lower weight, smaller dimensions and fewer moving parts. If you're currently thinking of getting a digital SLR, it's definitely worth checking out our list of advanced mirrorless compact system cameras too.
Five mirrorless CSC features to look for
Sensor size/resolution: Physically larger sensors tend to produce less noise at higher ISOs and produce stronger depth of field effects – it's easier to isolate your subjects against defocused backgrounds. Full-frame sensors are the biggest, followed by APS-C, Micro Four Thirds and 1-inch sensors. The resolution (megapixels) plays a part too, though most compact system cameras start at 16 megapixels, which is enough for all but the most demanding uses.
Lens range: Some CSC manufacturers give you a wider choice of lenses than others. This may not matter if you plan to use only the standard 'kit' lens supplied with the camera, but if you want to use telephotos, super-wide angle lenses or other specialised optics, it's a good idea to check the range (and price) of the lenses offered by each maker. As the longest-established format, Micro Four Thirds CSCs from Olympus and Panasonic offer the widest choice, though other makers like Samsung and Sony are working hard to catch up.
Electronic viewfinder: It's not essential for casual use, but an electronic viewfinder can be a major advantage if you intend to shoot a wide range of subjects in challenging conditions.
Phase-detection autofocus: CSC autofocus systems have got a lot faster in recent times, but conventional contrast-detection autofocus systems can struggle to keep up with rapid action. Increasingly, however, makers are introducing new, sensor-based phase-detection autofocus systems to speed things up considerably and approach or even exceed D-SLR focus speeds.
Articulating/touchscreens: Many photographers were sceptical about touchscreens when they started appearing on cameras, but they come in handy for quickly setting autofocus points, for example. Articulated touchscreens are doubly useful if you're shooting movies, macro subjects or any kind of low-angle shot.