Want the portability and convenience of a compact as well as the ability to attach different types of lenses? Then you should think about an interchangeable-lens compact system – or mirrorless – camera.

As the name suggests, these eschew the traditional mirror arrangement found in SLRs, but many now include the same kind of quality sensors and processors found in their mirrored peers.

They're more compact than SLRs, too, and some wonderfully dainty – but still high-performing – lenses have been developed to slim things down further. As with compacts, the CSC sector now caters for every type of photographer, from non-techy types to jobbing pros. If you're considering a CSC, here are some key considerations to help your buying decision.

Lens type

While you can change lenses on a CSC, it's important to remember that you can't swap CSC with SLR lenses unless you buy a special adapter – the lens mounts are quite different.

OM-D EM1
The OM-D E-M1 – it's not got the biggest sensor, but performance wise, this is still the king of high-end CSCs

Panasonic pioneered CSCs with the release of the G1 in September 2008, and together with Olympus, developed the popular Micro Four Thirds format for lenses. But here's the thing: Micro Four Thirds lenses won't work on a CSC from Canon, Nikon, Fujifilm and others, as these makers have their own mounts (though, again, you can buy special adapters).

Once you've got your head around this, there's a reasonable choice of lenses for your CSC. CSC lenses have tended to cost more than SLR equivalents, but prices are falling.

Viewfinders and screens

Cheaper CSCs lack a built-in viewfinder, requiring you to compose images on the rear screen.

Electronic viewfinders (EVFs) prevail on higher-end CSCs, and these can be fixed, tilting or even an electronic/optical hybrid, as on the Fujifilm X-Pro1.

Touchscreen features are often available, which is handy for quickly setting the focus point or changing settings. Most screens and EVFs boost image brightness in poorer light, making it easy to compose shots. In addition, EVFs are useful in bright light when the main screen image can be hard to see.

We recommend choosing a high resolution EVF of between 1,440,000 and 2,765,000 pixels and a main screen of at least 3-inches and 920,000 dots.

Sensor type

Although Micro Four Thirds sensors are physically smaller than the APS-C and full-frame sensors used in SLRs, there's an increasing number of CSCs with APS-C format sensors.

Sony A7R
The Sony A7R – compact size, interchangeable lenses, full-frame sensor...

It's even possible to get full-frame CSC in the shape of the Sony A7 and A7R. So by all means consider CSCs with bigger sensors if you want large, high-resolution images, but don't be put off by the smaller sensors inside Micro Four Thirds cameras.

There's more to CSC performance than pixel count and sensor size – access to a range of high-quality lenses is just as important. Smaller sensors also tend to mean smaller lenses!

Autofocus

Put simply, the mirrorless design of CSCs mean they mainly (but not exclusively) rely on contrast-detection AF, as opposed to the phase-detection system commonly used in SLRs.

Today's CSCs offer faster autofocus than their predecessors, though contrast-detection systems can struggle to keep up with very rapid action, which is one reason most sports photographers still use SLRs.

Higher end CSCs, such as the Olympus E-M1, now offer a hybrid phase/contrast detection system.

Consider a CSC with a fast maximum shutter speed and continuous shooting mode if you take a lot of action shots, but it's not really this camera type's forte.

Extra features

Carefully check these before buying. While many higher CSCs now feature built-in Wi-Fi connectivity, not all of them come with a built-in flash (though they usually have a hotshoe for adding one). Not all rear screens are touchscreen and vari-angled, either, though the Panasonic G6 ticks both boxes.

How much should I spend?

Around £350 / US£350 / AU$450 will get you an entry-level CSC such as the Canon EOS M, Olympus PEN E-PL5 or Panasonic DMC-GF3.

Olympus PEN E-PL5
The Olympus PEN E-PL5 – a stylish and popular CSC with plenty of imaging prowess

Around £420 / US$700 / AU$670 gets you a well-regarded mid-range model, such as the Panasonic G6, while the top-end Olympus OM-D E-M1 and full-frame Sony Alpha 7R cost £1,300 / US$1,400 / AU$1,570 and £1,700 / US$3850 / AU$2,400 respectively.

Anything else I should know?

As mentioned earlier, be careful to check out the choice of lenses available for any CSC you're interested in. There are significantly more Micro Four Thirds lenses than there are lenses for Canon and Nikon CSCs, as the two biggest camera makers are still more committed to the CSC market.