CAMERA FEATURES

Electronic shutter vs mechanical shutter

Some cameras feature an electronic shutter as well as the traditional mechanical shutter – but what's the difference? How do they work, and when should you use one rather than the other? Here's all you need to know about these two types of shutter.

A camera's shutter controls how long the sensor is exposed to light to record an image. The exposure time is determined by the shutter speed.

All Canon EOS cameras have a mechanical shutter, and some have an electronic shutter in addition, such as the EOS 90D and EOS-1D X Mark III. All EOS R System mirrorless cameras have both types of shutter. Here, we'll explain the difference between electronic shutters and mechanical shutters, how they work and the pros and cons of each.

What is the difference between an electronic shutter and a mechanical shutter?

In a modern DSLR or mirrorless camera, the mechanical shutter has two curtains or blinds, each made of several blades, that open to let light reach the sensor and then close at the end of the specified exposure time. It uses two curtains so that the exposure is consistent across the whole sensor. If there was only one, it would be like raising and then lowering a blind on your window – the first part of the sensor to be exposed would also be the last, and the exposure would be uneven. Instead, the process starts with the front curtain closed and the rear curtain open. The front curtain opens, starting the exposure, and after the set exposure time the rear curtain then closes to end the exposure. Both curtains move in the same direction (for example, top to bottom), so all parts of the sensor are exposed for the same length of time. Using two curtains also means that the exposure time is determined by the time gap between the first opening and the second closing, which can be very precisely controlled.

Unlike a mechanical shutter, an electronic shutter doesn't have any moving parts. Instead, the image information is gathered from the sensor over the specified exposure time, which can be much shorter than any mechanism could support. The catch, however, is that for technical reasons such as electronic bandwidth, the sensor data cannot be saved all at once but must be read off sequentially, one line (or several lines) of pixels at a time, in much like the way a scanner head moves down the bed of a flatbed scanner. As a result, the "shutter speed" (that is, exposure time) can be much faster but the readout speed can introduce limitations and potential problems.

An illustration of the image of a speeding train captured on a sensor. First, the complete image; second, a strip of the image being captured near the top, then one near the bottom of the image; and finally a distorted image caused by the train having moved between the middle two steps.

With a mechanical shutter, in principle, the entire sensor is exposed with a very short time elapsing between the first and second shutter curtains, capturing the whole of the frame at that moment (left). With an electronic shutter, however (middle two illustrations), the sensor data is read from top to bottom as if in slices, which is slower than the speed at which the mechanical shutter curtains moved – and during the time this takes, a very fast-moving object can have changed position. As a result, the moving object can look distorted in the recorded image (right). This is known as rolling shutter distortion.

What are the advantages of an electronic shutter?

There are several advantages to electronic shutters, but one of the most apparent is that they enable faster shutter speeds (shorter exposures) than mechanical shutters. In the EOS R3, for example, the fastest shutter speed with the mechanical shutter is 1/8000 sec, but with the electronic shutter it's 1/64000 sec. This makes it possible to freeze faster action and capture more split-second moments.

Electronic shutters can also increase the maximum continuous shooting rate. In the EOS R5 and EOS R6, for example, the rate jumps from 12fps (frames per second) with the mechanical shutter to 20fps with the electronic shutter, and in the EOS R3, the increase is even more dramatic – rising from 12fps with the mechanical shutter to up to 195fps with the electronic shutter.* 

In addition, because an electronic shutter has no moving parts, it can operate completely silently. This opens up new shooting opportunities, enabling photographers to shoot in places that would previously be off-limits. Some sports events such as tennis, snooker and golf tournaments, for example, have strict rules to prevent camera noises from distracting players at a crucial moment. With an electronic shutter, it's not an issue. A silent shutter also means that photographers can shoot during a theatre performance or a classical music concert without spoiling the occasion for the audience. Silent shooting can be an advantage in a wide variety of genres, from capturing baby portraits to photographing wedding ceremonies to documenting speeches and events.

Finally, a key advantage of a mirrorless camera over a DSLR is that there's no mirror movement to introduce vibration at the point of capture. An electronic shutter takes things a step further – because it has no moving parts, even the relatively tiny camera shake produced by "shutter shock" is eliminated.

What are the disadvantages of electronic shutters?

The most important potential problem with electronic shutters is the "rolling shutter" effect. Because the imaging information is read from the sensor pixels slice-by-slice, a very fast-moving subject can move during the time it takes to read the whole sensor. This results in the subject being distorted in the final image. A speeding train, for example, might be just halfway across the frame when the top line of pixels is read but near the edge of the frame by the time the bottom row is read. Consequently, the train will appear distorted in the image. The shutter speed (or, more accurately, exposure time) is still 1/8000 sec or whatever was set; it's just that each slice of the image is a very slightly different 1/8000th of a second.

Developments in sensor technology, such as the stacked design of the back-illuminated CMOS chip in the EOS R3, enable much faster readout speeds than before, greatly reducing rolling shutter distortion. Another new technology is the global shutter (or total shutter), which reads information from the whole of the sensor at once rather than line by line, but this technology is very complex, adds both image noise and cost, and can't yet produce very high-quality outputs, so although it is used in some video applications it is not practical for video or stills where image quality is the key requirement.

The flickering of some light sources, such as fluorescent and LED lights, can also cause banding when an electronic shutter is used because the brightness and colour of the scene changes during the period when the sensor is being read out. In a similar way, it can be difficult to sync a flash with an electronic shutter because most flashes produce a very bright but very brief light, meaning that the intensity of illumination is not sustained for the duration of the sensor readout. These issues, however, can also arise in certain circumstances with mechanical shutters, and the latest technologies in the EOS R3 include high-frequency flicker detection with the electronic shutter and also flash sync with the electronic shutter, at shutter speeds up to 1/180 sec (very close to the 1/200 sec possible with the mechanical shutter) and with either Canon Speedlites or third-party flashes.

Two diagrams showing the shutter sequence at shutter speeds lower than the camera's flash sync speed (left) and faster (right). In the former, there is a moment when the sensor is fully exposed, but in the latter there is no such moment and the sensor is exposed only in slices.

Even mechanical shutters can sync with flash only up to a certain shutter speed. Here's why. The left-hand diagram illustrates what happens at shutter speeds up to the camera's flash sync speed, for example 1/200 sec. Light enters the camera (1), and the shutter sequence (2) goes as follows. The front curtain (A) begins to open and at the end of the set exposure time the rear curtain (C) closes to end the exposure. For some period in the intervening time, the sensor is fully exposed (B) and can record the entire image as it is illuminated by the flash (3B). At shutter speeds faster than the camera's flash sync speed, 1/2000 sec for example (right-hand diagram), the rear curtain (C) starts to close before the front curtain (A) is fully open, so the sensor is exposed through a moving slit (B) rather than all at once. The image is exposed in "slices" (6 A-B-C) in very rapid succession, and there is no moment at which the whole frame is exposed at the same time. A short-duration flash, or the flickering of an artificial light source, can mean that the brightness and colour in the image vary from slice to slice, resulting in banding.

What are the advantages of a mechanical shutter?

Mechanical shutters have served photographers very well for many years and they still offer a couple of advantages over electronic shutters. First, although mechanical shutters also expose the sensor in "slices" at higher shutter speeds (see illustration above) and can therefore also suffer from banding or uneven exposure and variable colour under flickering light sources, this tends to occur significantly less with mechanical shutters than with electronic shutters.

Second, one of the most commonly claimed benefits of using a mechanical shutter is reduced rolling shutter distortion. The effect can still be present but tends to be much less perceptible with a mechanical shutter than with an electronic shutter on a camera with a relatively slow sensor readout speed. 

Finally, mechanical shutters usually offer flash sync speeds higher than those possible with an electronic shutter, although this rarely exceeds about 1/250 sec in any case because, at higher shutter speeds even with a mechanical shutter, the sensor is exposed through a moving slit and there is no moment when the whole of the frame is illuminated by the flash.

What are the disadvantages of mechanical shutters?

Because a mechanical shutter has parts that must move precisely with specific timings, the maximum shutter speed possible is significantly lower than with an electronic shutter. A mechanical shutter's response also isn't quite as fast as that of an electronic shutter, which again can be an issue when speed is of the essence. Consequently, you can't freeze very fast-moving subjects or fleeting moments quite as effectively with a mechanical shutter as with an electronic shutter.

In addition, the shifting of the mechanical shutter curtains produces a noise that in some circumstances may be quite intrusive or disruptive. It can also cause slight vibration that may lead to camera shake. This can be noticeable particularly if you're using telephoto lenses and relatively slow shutter speeds.

Lastly, the physical nature of mechanical shutters means that they will eventually wear out.

A diagram of a camera sensor with one line of pixel data being read at a time, alongside a second diagram of a sensor switched off, then on, then off again.

With the electronic shutters in use today (1), the sensor data is read out slice-by-slice. With a global shutter (2), the sensor is read all at once, so in effect the shutter goes from fully closed to completely open to fully closed again. This eliminates many of the shortcomings of electronic shutters, but there are considerable technical challenges in making this technology practical, including achieving sufficient sensor speed and data bandwidth for high-res imaging.

An EOS R3 shutter unit.

The mechanical shutter unit in an EOS R3 is state-of-the-art but there are physical limitations to the speed of any mechanism. It is mainly thanks to developments in sensor technologies that the camera achieves new benchmarks in shutter speed, flash sync speed and high-frequency flicker detection.

What is an electronic front curtain shutter?

Many recent cameras feature an Electronic Front-Curtain Shutter (EFCS) or Electronic First Shutter Curtain (EFSC). This is a mix of a mechanical and an electronic shutter. All Canon cameras with Live View since the EOS 40D (released in 2007) have this option, enabled by default as Silent LV Shooting. When EFCS is activated, the mechanical shutter is initially fully open (so light is reaching the sensor, which enables Live View). To take a picture, the exposure is started electronically, but it's ended by the mechanical shutter (second curtain) closing.

This has a number of benefits. It means that although the system isn't completely silent, it's not as noisy as using the fully mechanical shutter. Using the electronic shutter to start the exposure means the camera is very responsive, and shutter shock is avoided. (Camera shake caused by the second curtain is not recorded because this curtain ends the exposure.) EFCS can also enable a faster flash sync speed than using either the mechanical shutter or electronic shutter. On the EOS R3, for instance, the flash sync speed rises to 1/250 sec.

The drawback of using EFCS is that it can introduce some banding under flickering artificial light sources, although it's not usually as bad as when using the standard electronic shutter. In addition, the bokeh can become a little busy or "nervous" when fast shutter speeds are used. Finally, because the process still uses the mechanical second curtain, the fps remains the same as when using the mechanical shutter.

When should you use an electronic shutter and when should you use a mechanical shutter?

The electronic shutter is the one to go for when you need the fastest continuous shooting speed and/or the fastest shutter speed. It's also the logical choice when you need to be quiet, since it can operate completely silently. 

If you're shooting under artificial lighting, however, or using flash, then the mechanical shutter (or the Electronic Front-Curtain Shutter) might support higher shutter speeds. And if you find that the electronic shutter is resulting in rolling shutter distortion in stills, switching to the mechanical shutter or EFCS should resolve the issue.

It's also worth noting that, on all Canon EOS DSLRs and mirrorless cameras except for the EOS R3, the maximum bit depth drops from 14-bit with mechanical shutter to 12-bit with electronic shutter – meaning that when you shoot RAW using the electronic shutter, the camera is saving images with a slightly narrower range of colours and tones. This doesn't apply when you shoot JPEGs or HEIF files, because these file types already have a lower bit depth.

A golfer in white trousers and yellow shirt captured just after striking the ball. The shaft of the club looks curved.

A typical issue with electronic shutters is the rolling shutter effect, which distorts very fast-moving objects such as a spinning fan or propeller or the shaft of this golf club, so that it looks slightly curved. Taken on a Canon EOS-1D X Mark III with a Canon EF 70-200mm f/4L IS II USM lens at 200mm, 1/2700 sec, f/4 and ISO800.

The same golfer in white trousers and yellow shirt captured at the same moment, just after striking the ball. The shaft of the club looks straight.

The newly-developed back-illuminated stacked sensor in the EOS R3 can clear image data so quickly, rolling shutter effects are all but eliminated. Now photographers can take full advantage of the electronic shutter to freeze motion, at groundbreaking speeds up to 1/64000 sec, and in complete silence. Taken on a Canon EOS R3 with Canon RF 70-200mm F4L IS USM lens at 200mm, 1/2700 sec, f/4 and ISO800.

How to deal with rolling shutter distortion and banding

As mentioned, these issues are more prevalent with electronic shutters but can arise with mechanical shutters too, so simply switching to the latter (as commonly recommended) might not solve the problem.

Although some image-editing and video-editing software can correct for some of the distortion caused by rolling shutter, it's best to minimise it as much as possible at the shooting stage. If you're lucky, increasing the shutter speed may do the job. With video, you also need to increase the frame rate to make the camera scan the sensor faster.

Rolling shutter distortion is more pronounced when the subject movement is from one side of the frame to the other, perpendicular to the direction in which the sensor is read out. This means that changing the shooting angle so the subject is moving at 45° or even 90° to the camera can reduce the distortion.

The banding that may be seen in images captured in flickering light is a result of the light brightness varying over the time that the sensor is scanned. Most artificial light sources, particularly fluorescent lights and LEDs, flicker in phase with the AC electricity supply, so adjusting the shutter speed to 1/50 sec (1/60 sec in the USA) or 1/100 sec (1/125 sec in the USA) can resolve the problem, but if not, experiment with other shutter speeds to find one that matches the flicker cycle of the light source. 

Where this is available, it's also a good idea to activate your camera's anti-flicker feature, which sets the camera to detect flickering and to delay the shutter release slightly to avoid it during the exposure. Advances in Canon's sensor technology make the EOS R3 the first mirrorless EOS camera to offer high-frequency flicker detection when using the electronic shutter, which can eradicate banding when shooting under LED light sources.

*Custom high-speed continuous shooting setting, up to 195fps continuous bursts for up to 50 frames, available on EOS R3 with firmware update.

Shkruar nga Angela Nicholson and Alex Summersby


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