Now that we've seen how different shutter types work, we can look at some of the side-effects. The most obvious is rolling shutter: where your shutter rate is so slow that the world has moved on between the top of the sensor being exposed and the bottom of the sensor finally getting its turn. Theoretically this can happen with focal plane mechanical shutters if your subject moves fast enough but it's generally something you notice with the slower fully electronic shutter used for silent mode or movie shooting.

But the shutter rate can have an impact if your light changes during the course of your exposure, which it often does under artificial light and when you're shooting with flash.

Flash Sync Speeds

Shutter rate has a huge effect on the ability to use flash. Most flashes fire a very short, powerful burst of light. This is only effective if the entire sensor is exposed to the light while that burst is occurring.

Traditional xenon strobes use a very short-duration but powerful flash of light. This needs to occur while all of the shutter is collecting light (the cyan region), otherwise the shutter blades will obscure it.

Just as we saw with electronic shutters, your camera can offer shutter speeds faster than your shutter rate. However, to do this, the camera's 2nd curtain will start closing before the 1st curtain has finished opening. At this point, only a part of the sensor is exposed at any time, so there's no fully exposed moment to fire the flash.

Your camera's flash sync speed is essentially the speed of the shutter mechanism. Your camera can offer shutter speeds above this, but the 2nd curtain will be closing before the 1st has finished opening, so there's no time with the sensor fully exposed.

As a result, your shutter rate defines the fastest shutter speed at which you can fire a flash: your flash sync speed. The slower your shutter rate, the longer the exposure needed to provide a period with the sensor entirely exposed: this is why some cameras have slower flash sync speeds than others. Near-instantaneous leaf shutters allow very fast flash sync speeds because they exposure the whole sensor even at high shutter speeds but slower, focal-plane shutters are typically limited to around 1/200th of a second.

Motor driven (rather than spring actuated) shutters are even slower, which is why the Panasonic GM series could only flash sync at up to 1/50th of a second. Most electronic shutters are so slow as to prevent use with flash at all.

An exaggeratedly slow shutter rate (red) shows how the shutter rate ends up defining the shortest exposure time (fastest shutter speed) during which there's time to fire a flash. The flash sync speed (green) must always slightly exceed the shutter rate.

There are ways around this limitation. High speed sync modes work by either pulsing the flash (at lower power) throughout the exposure or by using a flash with a longer duration and trying to ensure it syncs with as much of the exposure time as possible.

Interaction with artificial lights

The other issue is the banding that can occur when shooting under artificial light. This is affected by three factors: shutter rate, shutter speed and the type of lighting you're shooting under.

It's not a totally different situation to the one described when discussing strobes. In the case of mains (A/C) powered lighting, rather than there being short burst of light, there's a cyclical pulsing of intensity. The degree to which artificial lights fluctuate depends on the technology they use.

Tungsten filaments stay warm and continue to glow during the half of the cycle where they're not being powered, so their flicker isn't usually noticeable. Fluorescent lights are more of a problem: they are significantly less bright during the phase change of the A/C cycle and are usually designed to flicker at much higher frequencies to make this less of a problem. Finally, the most basic LED lights can turn off and on completely, depending on how they're driven.

Shutter rate defines the number of bands you see

If your shutter were instant, you'd never see banding. You might end up sampling so little of the light's output that your image brightness varies, depending on which part of the flicker cycle you captured, but that intensity would affect the whole image, just as it does when using a short duration flash with a leaf shutter.

However, with a progressive shutter, the slower your shutter rate the more risk there is that different parts of your sensor will capture different parts of the light cycle (it's essentially the same problem as rolling shutter: capturing multiple slices of time. But in this case it's the brightness of the light that's changing with time, rather than the position of your subject).

If your shutter speed is short enough, you'll get banding, and the shutter rate will define how many cycles of the light you capture (and hence how many bands you'll see). This diagram represents a very simple LED, which switches on an off. With any luck you won't often encounter such an extreme situation.

With a really slow shutter rate, you risk capturing multiple cycles of the light's flickering: which you'll see as bands across your image. In fact, if you know the rate at which your lights flicker, you can measure your shutter rate by counting the bands.

Shutter speed defines the intensity of the banding

This is only a problem if your shutter speed is short, though. If your shutter speed is longer than one flicker cycle (a light and dark period), you shouldn't see any banding because the exposure will be long enough to average-out the flicker of the lights. But, as you use shutter speeds faster than one cycle (typically 1/120th of a second under most lighting on 60Hz power), you'll begin to see banding.

The further you go beyond this, the greater the intensity of that banding will be, because each part of the sensor will capture just one tiny part of the light's flicker. With a very short exposure you risk your sensor just sampling the darkest part of the flicker cycle, you'll get totally black bands across your image. So, under artificial light and fast shutter speeds, you're probably best off using your mechanical shutter, if you can.

Conclusion

What should be apparent is that, unless you're using a leaf shutter (which tend to be very fast and can affect the whole image in a uniform manner), your shutter can lead to a number of limitations, from rolling shutter to banding and problems with syncing flash. However, what should also be obvious is that, the faster your shutter rate, the fewer of these problems you'll encounter. And, now that we're starting to see electronic shutters approaching the shutter rates of mechanical shutters, they're only going to get better.