Digital cameras are usually used to take one shot at a time, but they generally offer a continuous shooting mode too. In this mode, the camera keeps taking shots in succession for as long as you hold down the shutter button.
Continuous shooting speeds are quoted in ‘fps’ (frames per second). Cheaper point and shoot cameras might only be able to manage 1-2 frames per second, while advanced professional models can achieve 10fps and more.
Cameras can’t keep on shooting at these speeds indefinitely. In continuous shooting mode image data is being captured faster than the camera can process it and save it to the memory card, slo cameras use a short term memory ‘buffer’ to store this data while you’re shooting. The buffer capacity is limited, so camera makers also quote the number of shots you can take in a burst before the camera has to stop or slow down to clear its buffer.
The buffer capacity varies enormously amongst cameras. General purpose cameras have a smaller buffer capacity than higher-end cameras aimed specifically at sports and action photographers.
RAW vs JPEG in continuous shooting
Whether you shoot RAW or JPEG images also makes a considerable difference. Many mid-range cameras can shoot 100+ JPEG images in a burst without slowing down but only 10-20 RAW files. If you want to shoot RAW files in bursts, you need a more expensive camera designed for the job.
Frame rate and buffer capacity are the two key specifications for rating a camera’s continuous shooting performance, but there are other features and technologies to consider.
Viewfinder blackout can be an issue in high-speed shooting. It’s inevitable with DSLRs because the mirror has to keep flipping up and down as the camera exposes each frame. Even so, the viewfinder blackout can be so brief that it doesn’t really hamper your shooting.
Viewfinder blackout is more of a problem for mirrorless cameras, which often suffer from a degree of viewfinder ‘lag’ on top. Only the more advanced/professional mirrorless cameras can eliminate blackout and approach the viewfinder responsiveness of a pro DSLR.
Silent and high-speed shooting
Increasingly, cameras are offering electronic shutters alongside mechanical shutters. Mechanical shutters are still better for freezing fast action because almost all electronic shutters have a fixed ‘scan time’ that’s longer than the duration of the exposure (the sensor is read in ‘strips’). But electronic shutters can be very useful for silent shooting and very high-speed capture up to 30-60fps. Both are very useful in sports photography.
Continuous shooting places heavy demands on the camera battery. It often involves the extra weight of a telephoto lens, which can unbalance the camera. Portrait photographers use continuous shooting modes too, generally with the camera held vertically, which can become uncomfortable after a while.
For all these reasons, many photographers use ‘battery grips’ (or just plain ‘grip’). Most mid-range and pro cameras have optional battery grips, and some pro models are designed with the grip integrated into the design.
A battery grip will add considerable extra battery capacity for extended shooting sessions, a bigger, more grippable body that’s better balanced with bigger lenses, and duplicated controls for shooting with the camera held vertically.
If you’re using the camera’s continuous shooting mode you’ll almost certainly want to use its continuous AF (C-AF) mode at the same time. In this mode, the camera focuses continually all the time the shutter button is held down, and not just in the instant before each exposure.
This is an area where manufacturers are making rapid advances and are in constant competition with each other.
The idea of ‘predictive autofocus’ has been around for a while. This is where the camera tracks the subject movement over time to predict where the focus point will be for each successive shot.
Different camera makers call their continuous AF technology different things. Sony calls its AF system ‘4D AF’, describing its ability to track subjects not just through 3D space but through time as well (the fourth dimension).
Advances in technology, processing and subject-recognition, however, mean that many cameras now offer subject-tracking AF, where they can lock on to a recognised object and follow it around the frame. This has developed into the latest Eye AF systems, where cameras can recognise and focus on human eyes in an instant. This is ideal for portrait, wedding and social photographers, especially with today’s full frame cameras and fast, wide-aperture lenses, both of which can produce very shallow depth of field.
For sports photography, cameras offer ‘groups’ of focus points for following fast-moving subjects. These may be called different things by different makers, such as ‘zone AF’ (Fujifilm) or Dynamic area AF (Nikon).