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Silent Shooting, Electronic Shutters And Banding

A look at tradeoffs that come with mirrorless cameras’ electronic shutters

If you’re a photographer using a mirrorless camera, you may have experimented with the camera settings that allow for totally silent shooting. This is accomplished by disabling the mechanical shutter so the camera makes exposures electronically. (A DSLR user can achieve the same result by switching to live view mode.) The major benefit of the electronic shutter is that there are no moving parts, so if you’re shooting in a quiet situation you can capture photos without making a sound or causing a disruption. What a benefit!

But, of course, nothing in this life is free. And while electronic shutters are certainly useful, they do come with a couple of major drawbacks. To overcome these drawbacks, you must first understand how electronic shutters work.

When using an electronic shutter, the camera’s sensor is capturing pixels row by row in sequence across the frame. This largely mimics the traditional method of a mechanical focal plane shutter working at high speed—which means in practice that a sliver of light travels across the sensor for the duration of the exposure, rather than the entirety of the sensor being captured at once. The faster the shutter speed, the smaller the sliver. Herein lies the problem with electronic shutters.

If you’re photographing a subject traveling at high speed across the frame—a moving car, for instance—you can see visible distortion as the moving subject and moving sliver of light come together. The moving car will appear warped because it has moved between the time one sliver of pixels was recorded and the time the next sliver of pixels is recorded. The resulting distortion is called rolling shutter, and it makes vertical lines appear crooked when the camera is moving and subjects appear warped if they’re moving quickly enough across the frame.

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This problem can be solved simply by switching the camera to its mechanical shutter or, in a pinch, panning with the moving subject. But, unfortunately, it’s not the only drawback to electronic shutters. The other one can happen even with a stationary subject. This problem is called banding, and it manifests as horizontal dark lines that alternate throughout the frame.

Why does banding occur with electronic shutters? Banding happens when electronic shutters are used to photograph subjects illuminated by LED lights—or frankly any electronic light that pulses on and off in rapid succession.

A brief detour into how lights work, if I may. Back in the old days, our houses and offices were illuminated by incandescent light bulbs in which electricity heated a metal element until it glowed brightly. Technically, this light also pulsed subtly, but because the element itself retained heat during the off cycles, the light never truly turned off between pulses. In practice, this made incandescent lights appear to be truly continuous.

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These days, however, LED light sources use a diode that turns on and off in rapid succession. It’s a simulation of a continuous light source. While in actuality LEDs are turning on and off, the cycle happens so fast that our eyes simply see the illumination as constant. Our cameras are not so easily fooled, however, and the problem appears when the camera is using an electronic shutter. Because of that aforementioned line by line capture, when the LEDs cycle off, the line of pixels being currently captured will appear underexposed. Repeat the process a few dozen times across the sensor and you’ll get an image with obvious banding.

The digital image sensor is exposed line by line over the course of, say, 1/500th of a second. During that time the LED light illuminating the scene may have cycled on and off 100 times, each instance producing a line of underexposed pixels. It’s a picture full of striped illumination, and it’s not good.

Example of the rolling shutter effect when a softball player swings their bat, the bat appears to be bent.

Such banding is most evident in out-of-focus areas of the image and in lighter areas of the image. Which means that subtle banding might be no big deal. But still, it’s never ideal. To solve it, you can switch to mechanical shutter and the problem goes away. But then, of course, you lose the silent shutter.

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Alternatively, you can slow the shutter speed until the banding all but disappears. With the sensor exposed to light for a longer duration, the cycling of the lights gets lost and the light appears as it does to our eyes: continuous. But, of course, now you may not be able to handhold your camera or freeze moving action. Another option is to avoid the LED light sources. You could override them with a strobe or switch the lights to use incandescent bulbs. Or, if the situation permits, you could leave banding behind simply by going outside and using the sunlight for the exposure.

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