What is Burst Rate? Simply put, burst rate is the number of consecutive shots that a camera can continuously take, before it slows down dramatically or completely stops shooting. Some users confuse Burst Rate with Frames per Second (fps) speeds, and they are not the same thing – shooting speed, or fps, dictates the speed at which you can take consecutive shots; Burst Rate dictates how many of those shots you can take in a continuous burst, without slowing down.
When a modern digital camera takes pictures, the data from the imaging sensor for each image first enters what you can think of as a digital "storage" area, called a buffer or buffer memory. From here, it is written to the camera's memory card. Since many cameras can shoot faster than the speed at which shots are written to the memory card, sequences of continuous shots are stored in this buffer, waiting to be written one at a time. How fast image files can be written, and how large the buffer space is, are key factors in a camera's available Burst Rate.
Top of the line systems like Canon's EOS-1D series (see chart on page 2) always have the fastest possible throughput rates to capture the image, move the data, and save it to the card, making room for the next batch of images. A point and shoot camera, for example, will not perform with the same efficiency.
The speed at which successive photographs can be captured depends on a variety of factors, mainly the "throughput" speed – how fast information moves from one part of the camera's electronics to the next – and the processing power of the camera. The size of the images matters too; the larger the in-camera file size of an image, the fewer you will be able to shoot in a row, before the buffer fills. Comparing a camera's Burst Rate specs, you will almost always find it is lower for RAW files than for JPEGs, and that is in part because Canon's .CR2 (RAW) files are about 3x the size of a high-quality JPEG. When shooting JPEGs, disabling certain features such as "strong" High ISO Noise Reduction may allow for a faster rate of capture, and more consecutive images to be shot in a single burst. Memory cards have a role here as well; the faster a card is at writing data and allowing access to the card, the longer the burst rate can be sustained.
No matter what your camera's burst rate is, if you shoot continuously and fill the buffer, the camera will either slow down dramatically or stop altogether, and the camera's "card busy" light will begin to blink, indicating it is busy writing to the memory card. As space in the buffer becomes available, you can again continue shooting. You will not get a "full burst rate" back until the card's "busy light" stops blinking completely.
Cameras capable of faster continuous burst rates are ideal in situations when you expect to need to shoot continuously, from time to time, without being forced to stop. Environments where this is crucial include sporting events, auto racing, and wildlife photography. You will find that cameras with fast continuous burst rates will come in handy in any situation where there is a brief window of opportunity to get the shot that you want; weddings and photographing children are great examples. Instead of trying to time the perfect moment to shoot, which sometimes might be near impossible, you can shoot from right before the action starts through to when you are confident you can put the camera down.
Previous generations of Canon EOS cameras only offered a single-digit countdown in the viewfinder of remaining images that could be buffered, starting with 9. Currently, mid-range and high-end EOS models have a two-digit countdown, which gives the user a more meaningful idea of how long he or she can continuously fire the camera before it will slow down significantly or stop altogether until space is made available within the buffer memory area.