We’ve learned how to control adjust the overall exposure of a scene. Now let’s learn about shutter speed, one of the factors that contribute to the amount of light in a photo.
What is shutter speed?
Shutter speed is simply how fast the shutter of your camera moves. The shutter keeps light out. When it opens, light comes in.
And when it closes, that light stops coming in ‐ this is usually when the photo is considered “taken”
The faster that shutter open and closes, the less opportunity light has to enter the camera and be part of the photo.
How is shutter speed measured?
Shutter speed is measured in seconds; actually, you’ll almost always be thinking of them as fractions of seconds.
For example, a shutter speed of 1/200 can be paraphrased as: “The shutter was open for 1/200th of a second”
A slower shutter speed is 1/10, or: one-tenth of a second.
If the shutter speed is in whole seconds, such as 3 seconds, that is considered to be very slow.
How does shutter speed affect exposure?
Let’s repeat an exercise that we’ve done in the previous chapters on exposure:
- Point your camera to something dark
- Quickly move it to something light
- Try to snap a photo before it properly auto exposes.
Here’s what I got:
Why is everything blurry?
When your camera was exposing for the dark scene, it slowed its shutter speed to let in enough light. When you moved it suddenly, the camera didn’t have time to speed up its shutter, causing motion blur.
Why does a slow shutter speed result in motion blur?
Think of how a photo is created in the first place: by light reflecting off of objects and into the camera sensor, which prints the image of that light to file.
When the shutter lets a long burst of light – in other words, increasing the number of reflections bouncing off of a given object – and that object moves, you have an image of that object in motion.
(sorry, I’ll stop pretending to be a science reference now)
How fast does the shutter speed need to be to prevent motion blur?
It depends on the situation. If your camera is perfectly still. And the object you photograph is also still, then your shutter speed can be about as slow as you want it to be.
Now, if that object is moving, then you have a problem. Let’s pretend you’re trying to take a photo of an object that moves a meter a second. If your camera is perfectly still and your shutter speed is 1s, then the camera sensor will record a meter long streak caused by the light bouncing off the object as it moves for that second.
So, unless your shutter breaks the laws of physics and opens and shuts at an instantaneous rate (a shutter speed of 0), the object will have some blur in the final image.
I promise, this is the last of the math we’ll have to cover for now
Unless of course, your camera is moving 1 meter a second in the exact same direction. Then that object will be perfectly sharp…though if everything else in the scene is stationary, then those will now be motion blurred. And this is assuming you’re able to keep your hands from shaking up and down…
So basically, there’s no magic number. You’re going to figure it out through eyeballing it and after taking your fair share of blurry pictures.
The most important takeaway is: if you don’t want blur to ruin a photo, then kick up the shutter speed as much as you possibly can.
Come on, there must be some kind of general tip
OK, one rule a number of pros go by is: try not to set your shutter speed slower than your focal length.
This means if you are using a 35mm lens, try not to set your shutter speed slower than 1/35. If you’re using a 200mm lens, don’t go slower than 1/200 (which is why telephoto lenses often have image stabilization built-in).
Why is this? It’s a matter of perspective: think of how an all-star running back looks like when he sprints for a 100-yard touchdown as you’re watching from the top of the stadium. Now imagine what that looks like if you’re watching it on the sidelines, five feet away from him.
In Program Mode, my camera keeps setting the shutter speed to a rate too slow for me to keep steady
This is why we’re going to ditch Program mode and learn how to use shutter priority.