With the increasing dominance of mirrorless cameras, particularly those with larger sensors, Photo Review tech editor Margaret Brown looks at six key factors to consider when buying an interchangeable lens camera.

In the decade since we last published advice on buying a DSLR camera, the camera market has undergone some radical changes. Most significant of them has been the increasing dominance of mirrorless cameras in the market, particularly those with larger sensors that are taking over the top end of the interchangeable-lens camera (ILC) market.

Photographers who have been waiting until the ‘right’ model came along to buy into their first camera system are faced with some interesting choices, the first of which will be between a DSLR and a mirrorless camera with similar capabilities. Buying a DSLR is likely to be cheaper initially. But opting for a mirrorless system should provide you with a smaller, lighter and more versatile camera that is arguably more ‘future-proof’. That’s the way the market is trending. But you need to know what you’re buying into.

Mirrorless cameras are structurally simpler and easier to make than DSLRs. Eliminating the mirror box and optical viewfinder enables manufacturers to produce more compact camera bodies with fewer components to complicate production.

But it also means they need electronic viewfinders (EVFs) to replace the optical viewfinders in DSLRs. (Note: it’s probably best to avoid cameras without viewfinders if you take pictures or shoot video outdoors.) Today’s EVFs are great to use, particularly for shooting video. They show you exactly what the sensor is recording, including the actual exposure brightness, colour balance, contrast and saturation that will be recorded.

The latest mirrorless cameras also have advanced ‘hybrid’ autofocusing systems that combine data from arrays of phase detection sensors on the surface of the sensor chip coupled with contrast-detection arrays that cover most of the frame. Subject detection and tracking can be lightning-fast with these systems, which also benefit from sophisticated face and eye detection algorithms.

Fujifilm’s new X-T200 mirrorless ILC

Regardless of whether you choose DSLR or mirrorless, the combination of price, performance and sensor size/resolution offered by most ILC models today is more than ‘good enough’ to satisfy even demanding enthusiasts. You should also be able to find equipment that feels comfortable to hold and operate, is compact and light enough to carry and offers the flexibility and performance to allow you to work creatively.

However, when you’re forking out a thousand dollars (or more) of your hard-earned cash, you need to know that you’re getting a worthwhile bit of gear. Here are some of the factors you should consider.

1. Sensor Size

This is the main factor that differentiates photography with a ‘real’ camera from snapping shots with a smartphone. Picture quality and exposure flexibility are strongly influenced by the size of the sensor and the size of each light-capturing photosite on it. The larger the photosite’s surface area, the more light it can capture and the more information it can record. The more information that goes to the camera’s image processor, the greater the dynamic (tonal) range in the resulting image – and the better the picture quality.

The differences are most obvious in shots taken in bright, contrasty conditions as well as in dim lighting. In bright lighting, the tiny sensors in smartphones struggle to record details in the brightest and darkest areas. The resulting pictures usually have blocked-up shadows and blown-out highlights and, when no detail is recorded, there is no way to tweak the image to improve the situation.

This doesn’t necessarily mean you need the largest sensors available. They come with significant penalties. The larger the sensor the larger, heavier and more expensive the resulting cameras and larger and heavier the lenses needed to match them. Sure, they can provide higher resolution; but how much resolution do you actually need?

2. Megapixel Resolution

Until recently, most advertising material and much of the media hype has focused on the number of megapixels the camera supports. However, today the megapixel count is relatively unimportant when buying a camera because the lowest resolution of today’s interchangeable-lens cameras is between 20 and 30 megapixels. This is generally enough for most photographers, particularly those who use cropped-sensor cameras with APS-C (approximately 24 x 15 mm) or Micro Four Thirds (17.3 x 13.0 mm) sensors.

Twenty megapixels provides plenty of scope for editing and printing at A2 size, which is the largest most photo enthusiasts will use. In full-frame cameras, it also means relatively large photosites, with excellent light-gathering potential.

Be wary of buying into ultra-high resolution cameras unless you have a genuine need for such high resolution. High pixel counts result in large image files that take time to process and space to store. Even though storage is relatively cheap, it simply doesn’t make sense to pay more for resolution you don’t need and can’t utilise.

Support for raw file capture is virtually universal these days, enabling photographers to extract the maximum amount of image data at the editing stage so there’s little incentive to aim higher, unless you want bragging rights.

3. Brand Loyalty

Buying into a particular brand has plusses and minuses. Photographers who already own a DSLR plus a suite of interchangeable lenses will probably be lured towards mirrorless cameras from the same manufacturer. And most manufacturers in this category offer adaptors that let you use your DSLR lenses on a new mirrorless body – without compromising their performance.

It makes both logical and financial sense to buy a body that will accept the lenses you already have. However, it’s not necessarily the best option for the following reasons:

If you’ve been using an ‘APS-C’ type DSLR with a crop factor of 1.5x, your lenses may not be suitable for use on a ‘full-frame’ mirrorless camera with a 36 x 24 mm sensor. This is because they don’t cover the same field of view, which means the edges and corners of the frame will be darkened on the new camera. Some models can detect the APS-C lenses and will switch automatically to using a cropped area of the frame to prevent this vignetting. But that can’t be guaranteed.

Some manufacturers have two separate camera lines, one for cameras with full frame sensors and one for cropped sensor models. Only Sony makes lenses that can be used with both lines (and even some of their lenses are not fully compatible with both).

Olympus and Panasonic have, together, developed the Micro Four Thirds system, based on cameras with 17.3 x 13.0 mm sensors, which are roughly one quarter the size of the 35mm format. By keeping resolution to around 20 megapixels, these cameras provide the benefit of light and compact bodies and lenses coupled with professional level performance for both stills and video capture.

However, some of the in-camera technologies, such as coupling camera and lens stabilisation, remain brand specific. Olympus lenses can’t integrate with the in-body stabilisation systems in Panasonic cameras, and vice versa.

4. Video

The ability to record 4K video is universal today – in both cameras and phones – so there’s really no need to seek it out unless you shoot a lot of movies and/or plan to use your camera for professional (or semi-professional) projects. There’s not much difference in the range of recording functions offered between cameras and phones, although cameras should produce better picture quality because of their larger sensors and more sophisticated lenses.

Most cameras and phones are limited to recording 4K clips at around 25 frames/second, with faster frame rates only available for Full HD (1920 x 1080 pixels) recording.  If you like to shoot video, it’s worth checking the resolutions, formats and frame rates available when you’re checking out any camera or phone.

The electronic viewfinders (EVFs) in mirrorless cameras are easier to use for video than DSLRs, which require you to frame shots using the LCD monitor. LCDs are notoriously difficult to ‘read’ in bright outdoor lighting so shooting video with a DSLR can become a ‘point and guess’ exercise in such conditions.

Be prepared to pay more for cameras that support professional recording formats (like CinemaDNG) and those that include high bit depth recording modes and Log and Flat profiles. Stereo audio recording is relatively common but some cameras lack microphone sockets for fitting an accessory mic. Headphone ports are also handy for monitoring audio recordings as you shoot.

Photographers who shoot a mix of stills and video will be pleased to know they can ‘grab’ 8-megapixel still frames in JPEG format from 4K video clips and use them for other purposes, including printing at up to A3 size. These frames can also be shared easily on social networks.

5. Lenses

Most entry- and mid-level cameras are sold with at least one ‘kit’ lens; generally a medium-range zoom lens that spans from a modest wide angle to a short telephoto focal length. While kit lenses were often fairly basic in the past, today most manufacturers are offering lenses with decent build quality and acceptable performance.

The main downsides of kit lenses are seen as the tendency to use more plastic in their construction coupled with less glass, which leads to slower lenses. Countering the first point, the polycarbonate plastics used in today’s cameras and lenses are usually high quality and very robust. However, plastic lens mounts are best avoided if you want to keep the lens for a long time and expect to put it on and take it off the camera fairly frequently. Metal mounts are much more durable and reliable.

Use of plastic in lens barrels has the advantage of allowing lighter and cheaper lenses to be made without significantly compromising durability and performance.  Some largely-plastic lenses are at least partially weather-sealed although not necessarily as well-sealed as metal lenses.

Aim to build up a collection of lenses to cater for the types of photos you want to capture. As well as a ‘walkaround’ standard zoom lens, you might need a short telephoto prime (single focal length) lens for portraiture, a longer telephoto lens for sports and wildlife and the longest lens you can afford for bird photography. Wide angle lenses are popular for landscapes and cityscapes and macro lenses for close-ups. Zooms are more versatile than primes as a rule but primes often represent better performance and value for money if you can find one that suits a specific purpose,

Lens ‘speed’ (the size of the maximum aperture) can make a difference in two factors: the ability to isolate subjects from distracting backgrounds and the ability to use your camera handheld in dim lighting. Zooms are usually slower than equivalent prime lenses. Fast lenses tend to be heavy and come at premium prices so if lens speed isn’t particularly important to you, a lens with an f/4 maximum aperture should be good enough.

6. Stabilisation

Regardless of whether it’s built into the camera body (sensor shift IBIS) or in the lens (optical or lens-shift), stabilisation has become essential for contemporary photographers and videographers. Many of the latest cameras provide both and, provided you have the same brand for camera and lens, most will allow them to work together to give you a bit of extra stability. The latest cameras can provide up to seven stops of shake correction through these ‘dual IS’ systems.

Five-axis stabilisation will provide corrections for up/down, side-to-side and rotational movements. This will enable you to shoot hand-held in lower light levels and use lower ISO settings, which means reduced noise and better picture quality.

Look for some of the latest innovations that have resulted from improvements to camera stabilisation systems, such as high-resolution modes that combine a sequence of shots captured in rapid succession to produce an image with much higher resolution than the camera’s sensor offers. Multi-shot modes have also been used to improve colour reproduction and reduce image noise. Focus stacking, which combines a sequence of shots with different focus settings into a single image that is sharp from foreground to background, is a real asset for macro photography.

See latest DSLR camera reviews

See latest Mirrorless camera reviews

Article by Margaret Brown