Drive Modes, Burst Rates and Frames Per Second

Drive Modes, Burst Rates and Frames Per Second

 To capture action sequences make use of the drive mode in your camera. Here, continuous mode has been set at 4 frames-per-second and the camera was moved along with the action, set at 1/500 second shutter speed. You can use this technique to pick the best shot in the set or to show how the action unfolds in a sequence of images.

Photos copyright George Schaub All Rights Reserved

There are generally three, and sometimes four options in the “drive” mode in a digital camera, and each has a specific benefit. Single is probably the drive mode you would most commonly use. Set this and the camera will not “allow’ you to expose unless focus has been confirmed and you get one shutter release for each time you apply pressure to the shutter release button. This is ideal for portraits, landscapes and other scenes where the subject will not move. Think of it as a “stationary” mode.

Then there are one (or two) continuous advance modes, which means that, within limits, the shutter will fire for as long as you keep pressure on the shutter release. You set this for bracketing modes (which means that the shutter will fire three, or however many shots you have set in the bracketing sequence) where one pressure will fire off the sequence of shots. This mode is also used as a kind of still video mode (many shots in sequence.) And then there’s the self-timer mode, which delays shutter release for a set period of time after you press the release.

There may be a difference in file size recorded if you have the option for “continuous low” and “continuous high” drive modes. In some cameras, because of the limitations of the processor, continuous low may allow you to record at whatever resolution you have selected, be it in Raw or JPEG format. In some, when choosing high, you get a faster framing rate (stated as “frames per second”) but the camera will record with a lower file size, and may even limit you to shooting in JPEG format. Again, this has to do with the camera processor and how much information it can handle quickly. Check the specs on your camera to see how this is handled.

The speed at which digital cameras can record images has increased substantially over the past few years. First there’s shutter speed, which in quite a few cameras can be as fast as 1/8000 second, a slice of life that is quite hard to imagine. In short, the camera can now “see” action in ways that the human eye cannot, and can deliver split seconds of action that sports and wildlife photographers could only dream of in the past.

There are two more factors—the speed at which cameras can process and write to the memory card (and the speed at which the card can “receive” the information) and the number of shots you can get  in a sequence, known as the “burst rate.”

Video has changed the game when it comes to still photography, at least in terms of how memory cards can “read and write” the information that comes from the camera. The latest cards are designed for gathering information quickly from even the most advanced digital cameras. This is especially helpful when working in Raw format, as the information from each shot tends to be fairly large, and having a highly rated speed card will open up the most creative continuous shooting capabilities.  This also depends on the image processor in the camera and how fast it can process the images as you record them. In some cases the card can handle more than the camera can deliver, and the rule is that the slowest part of the process will determine the overall speed.

That’s where the burst rate comes into play. The burst rate tells you how many shots you can make in a set period of time before the camera calls a halt while it processes the images you have shot. These images are stored in what’s called a buffer, a kind of waiting room while the processor churns through all the information you have sent its way. Once you reach the burst limit everything comes to a halt (including further shooting) until that buffer is cleared. (This also happens when shooting long time exposures, exposures where you have applied a lot of noise reduction and other processor intensive tasks.)

The time period mentioned above is another factor. For example, burst rates may be stated as “eight shots per second for 12 exposures”, or “4 shots per second for 18 exposures” and so forth. The shutter speed also comes into play. Naturally, the longer the shutter speed the less shots you can get into a shots-per-second burst. If exposure is ½ second you can't get more than two shots a second. But there's another thing to consider--generally, the longer the exposure, the longer the processing time. In some cameras the processing time is equivalent, roughly, to the exposure time. It all depends on which generation image processor you have. The latest processors are much more burst and speed capable than in the past.

ND Filters-- Built-in or Add-on

In light control you have two tools, one of which is fairly open-ended and the other of which is fairly limited. The latter is the aperture, where there is a range of perhaps 6 or 7 stops, with each stop representing a halving or doubling of the amount of light coming through. The shutter speed offers a much wider range, and may be, with a system that allows you to shoot from 30 seconds to 1/8000 second automatically, a range of 18 stops (!) So, when adjusting for the light at hand you have more leeway when setting shutter speed than when setting aperture.

For example, let’s say you are working in dim light. You open the aperture on your lens to its widest setting, say f/4. That’s as much light as the aperture will bring to the table. You have maxed out on the quality limit of your ISO, say that's at ISO 800, and you know that going with more ISO will diminish picture quality to the point where it's not worth it. 

But the shutter speed can be set at a very slow speed, even as slow as a few seconds. Of course you need a tripod to keep the picture steady, but shutter speed will not limit you in making the shot, even though aperture “quit” on the deal at f/4 and ISO above 800 might just have been too noisy.

However, let’s say you want to create the image effect of a slow shutter speed in bright light. You might want to capture a “flow motion” effect on a waterfall or a stream, or pan, follow a subject in motion as you make the shot, a runner or a speeding car at a race. That is more challenging, as the aperture may not allow you to create that effect because it can only limit the light coming through even when closed down to its minimum aperture. And when shooting for that effect only a certain range of shutter speeds will do—from about 1/15 to ¼ sec.

For example, say you take a reading of a waterfall in bright light and know that to gain the effect of flowing water you need a shutter speed of about 1/8 to ¼ second. You set the ISO at its lowest, since you do not want more sensitivity on the sensor, you want less. And even at the minimum aperture on your lens, say f/16, the shutter speed comes up at 1/60 sec. How can you “lose” three steps to 1/8 sec or four steps to ¼ sec.

This photo was made using the minimum aperture of the lens, f/22, at ISO 100, with a 4X ND filter over the lens, at 1/8 second, yielding a flow effect on this waterfall. Photo copyright George Schaub, all rights reserved.

You solve this problem with a neutral-density (ND) filter over your lens to diminish the amount of light coming through the lens. An ND filter is “neutral” in that it does not change the color of the light, and offers a “density” or degree of darkening effect. The filter comes in various strengths, in multiples of 2, where a 2X gives you a one-EV gain, a 4X, 2 EV and so forth. Thus, using a 4X ND filter on the example above, you could shoot the scene in the same light and at the same ISO at f/16 at 1/15 second and with an 8X filter it would be f/16 at ¼ sec, yielding the flow effect you desire and the shutter speed used here.

A number of cameras, including Canon's G series digicams, now offer this as a built-in, and using the menu you can choose the power of the ND as needed. Also note that this is one control—the shutter speed effect-- you can’t apply after exposure in any image processing software.

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