Your iPhone camera is pretty good at taking photos automatically. You just point it, shoot, and the camera works out all the tricky stuff. But what is actually going on in there? How does it take the light that you see and render it as an image on the screen?
In this short series, we’ll look at the physical parts of a camera — the aperture, the shutter, the magnification of the lens, and so on — and see how they affect the final image. Today’s topic: shutter speed.
What is a shutter?
In a film camera, a shutter protects the film from light until you’re ready to snap a photo. Then, when you press the shutter release button, it opens up for a fraction of a second, and lets light from the lens fall onto the film. The film then records the light falling on it. The longer the shutter is open, the more light falls on the film, and the lighter/brighter the image.
If you take a photo at night, you need to leave the shutter open longer, in order to gather enough light to record an image. In bright sunlight, you need a shutter that can open for a tiny fraction of a second in order to avoid too much light, which would result in a washed-out, white image.
The sensor in a digital camera like your iPhone works the exact same way, with one exception. Whereas a film camera’s shutter only opens to expose the film, the shutter in your iPhone is open all the time so that that the sensor can receive light, and turn it into a live image on your screen. When you press the shutter release button, the shutter closes for a moment before opening again to expose the shot.
The iPhone uses an electronic shutter, which is incorporated into the sensor. Effectively, this “shutter” is just the sensor switching pixels off and on again, which is why it can switch on and off so fast. Film cameras use an actual physical barrier between light and film, which has to open or close. Most regular digital cameras do the same. The upper limit for most DSLRs is a shutter speed of around 1/2,000 or perhaps 1/4,000 sec, with high-end ones hitting 1/8,000 sec.
iPhone shutter speed
The length of time that the shutter remains open is called the shutter speed, measured in seconds, or fractions thereof. On the iPhone 7, for instance, the shutter speed can run from 1/4 (a quarter) of a second, up to a truly mind-boggling 1/10,000 (one ten thousandth) of a second. This is using the manual camera in the Lightroom app. A quarter of a second is slow enough to let you shoot in quite murky indoor conditions, and 1/10,000 is more than short enough for the very brightest of days at the beach.
But, shutter speed doesn’t just affect how much light is allowed to reach the iPhone’s camera sensor.
Shutter speed and freezing action
Imagine that you take a photo with a shutter speed of a quarter second. Now, imagine that you’re snapping a picture of a motorbike speeding past your lens, from side to side. That bike actually moves quite a lot in the quarter-second that the shutter is open, gathering light. In fact, the bike will move enough to blur across the frame. If you manage to hold the camera steady, so that the background is sharp, this can make for a nice special effect.
Another neat effect is called panning. This is where you set a slow-ish shutter speed (1/60 sec, more or less, maybe a little slower) and move the camera to follow the motorbike. In this case, the bike stays sharp, and the background blurs, because the background is moving in relation to the camera. Twist from the hips, and practice a lot.
The converse is also true. A very fast shutter speed (over 1/1,000th sec is usually enough) will freeze most action. If you want to freeze bullets or droplets of water, you’ll need more specialized gear, but for all sports, the iPhone is more than capable.
Shutter speed and camera shake
A slow shutter speed can be used to blur action in your photo, but only if you hold the camera steady enough to keep the rest of the picture sharp. If you wobble, then then entire image is blurred. This is called camera shake, and is almost always something to be avoided.
The best antidote to camera shake is a tripod, or a faster shutter speed. You can also practice holding the camera steady. This is tricky with an iPhone, as you usually hold it at arm’s length. With a regular camera, you can keep your elbows tight to your sides as you peer through the viewfinder.
There are other aspects of shutter speed you might want to look into. How it works (or doesn’t work) with flash, for example. But for iPhone photography, the above covers most of what you need to know. If you want to experiment with setting the shutter speed yourself, you’ll need a manual camera app to do it, or just dig out your old camera. Lightroom is my favorite iPhone camera app right now, and Halide is also pretty good. Have fun.