They come in a bewildering array of shapes, sizes and prices, so how do you choose the best CSC (compact system camera)?

We've produced this guide to explain how mirrorless compact system cameras work and how to choose the right one for you. Our camera home page will keep you up to date with all the latest camera reviews, but here's where we explain how to find the best CSC for you and what you need to look for.

Alternatively, if you already know the best CSC type for your needs, you can go straight to our top 5 lists:

Compact system cameras vs D-SLRs

The big appeal CSCs is that you can also change lenses and enjoy cutting-edge imaging performance, but with a much smaller and lighter camera body. So they offer SLR-like versatility in a more streamlined and discreet package.

Best mirrorless compact system camera
It looks like a DSLR, doesn't it? But between the lens and the sensor the Olympus OM-D E-M1 has no mirror

Olympus OM-D E-M1 review

CSCs are also known as mirrorless cameras because they don't have the reflex mirror and optical pentaprism or pentamirror viewfinder of SLRs. Instead, the live image captured by the image sensor is fed to the LCD display, just as it is with a compact digital camera.

Faster focusing

In the past this has meant that compact system cameras have had to rely on contrast-detection autofocus systems which are very precise but slower than the phase-detection autofocus systems used on digital SLRs. Recently, though, manufacturers like Fuji, Sony and Olympus have been adding phase-detection capability to their camera sensors, so the gap in autofocus performance with the best CSC cameras is closing rapidly.

Electronic viewfinders

It's not always easy to see an LCD screen in bright light, however, which is why many compact system cameras also have electronic viewfinders (EVFs). These are miniature LCD screens which you view through an eyepiece. You find EVFs on more advanced compact system cameras.

Best mirrorless compact system camera
EVFs (electronic viewfinders) are tiny LCD displays viewed through a regular viewfinder eyepiece

Otherwise, compact system cameras offer the same buying decisions as digital SLRs. The key factors are the user level (novice, enthusiast, expert), the sensor size and resolution and the lens fitting. Each manufacturer uses its own bespoke lens mount, so it's a good idea to check to range and cost of the lenses available before choosing a camera. The best CSC isn't necessarily the camera with the biggest specs, but the one with the right range of lenses.

Sensor size

As with other types of camera, the sensor size is the most important factor for image quality, followed by the resolution (in megapixels).

Until recently, most compact system cameras used either Micro Four Thirds sensors or APS-C sensors.

The Micro Four Thirds format was developed jointly by Olympus and Panasonic and is used in all their compact system cameras. It's a little smaller than APS-C, but the image quality is still very high and it does mean that the cameras and lenses are more compact.

Compact system cameras with APS-C sensors are more common, however, and deliver images with the same quality as APS-C digital SLRs. Samsung, Sony and Fuji use APS-C sensors.

Best mirrorless compact system camera
Olympus and Panasonic use Micro Four Thirds sensors. Other makers like Fuji use slightly larger APS-C sensors.

Panasonic GX7 review

There are now compact system cameras with both smaller and larger sensors than this, though. Pentax started this trend with the Pentax Q series, which has 1/2.3-inch or 1/1/7-inch sensors – too close to those in regular compact cameras to be taken seriously alongside the best CSC models. But the 1-inch sensors used by the Nikon 1 and now the Samsung NX Mini offer an interesting compromise between size and quality.