Let’s have a look at the second part of the “exposure triangle” to get some more photography foundation laid: Shutter Speed. We already learned about Aperture in Part I of the series:
Part III will be an upcoming article about ISO, and then we have all parts together.
So, let’s talk about shutter speed. It is easy to learn, as we don’t have any unexpected side effects when controlling the shutter speed. As you may remember, the aperture had the Depth of Field (DoF) side effect, and ISO has image noise as a side effect. And shutter speed has the freezing-motion effect, or lack of the same, but that seems to be more of an intuitive side effect.
But we should start with explaining what the shutter is. The shutter is build from metal blades which open and close the opening in front of the sensor for a set duration, to let a specific amount of light pass on to the sensor. The metal blades form two “curtains”, so the shutter is actually made of two separate shutters. That is important to know as soon as you look at including flash as a light source into your photography.
Some ancient or very expensive cameras have a leaf shutter, but that is a rare exception. The manufacturer carefully handcraft the shutter into the lens and it works more like an aperture in a circular motion, rather than from left to right or top to bottom, as the curtains of a traditional shutter work. I’ll disregard the leaf shutters for the remaining part of the article as they are not common.
How does a shutter look like?
I think at this stage a video is very helpful; I found one which brilliantly shows how these two curtains of a traditional shutter interact:
If you want to see (and hear!) shutters in action, search for slow motion videos of camera shutters, interesting!
What does the shutter control?
When you control the shutter speed, you control how much light is passing through the lens on to the sensor before the shutter closes and blocks the light path. You directly control the brightness of the image. Most modern cameras can control this time up to a very tiny fraction of a second, e.g. 1⁄8000 of a second, and beyond (with an electronic shutter, more on that further down).
The shorter the time the shutter is open, the less light is exposing the sensor, making the resulting image darker. The longer the shutter speed, the more light passes through and the image gets brighter.
Measurements of Shutter Speed
The intervals of shutter speeds are marked as a fraction of a second, e.g. 1⁄250, which means a 250th of a second. As soon as we go past the second, we see the quotation mark behind the number: 1” means 1 seconds, 2” would be a shutter speed of 2 seconds. When you are in shutter priority mode (S or Tv on your camera), the longest time you can usually set is something around 30 seconds. If you want to expose even longer, you can do that by using the manual mode. In this mode, you can set a ‘BULB’ shutter ‘speed’, which means the shutter stays open for as long as you hold down the shutter button. Thinking of that, use a cable release to avoid camera shake. Highly recommended with any longer shutter speed! Some cameras have modes where you press the shutter button to start the exposure (curtain open), and with the next shutter button click the curtains close. Still very prone to camera shake, use a cable release or an electronic release (e.g. a mobile phone app for remote control of your camera).
What shutter speed should I select?
It depends on the type of subject and what effect you want to achieve. And how much light you have at your disposal. Let us explore what images would look like with a slow or a fast shutter speed.
A fast shutter speed freezes motion:
With slow shutter speed, it will blur any fast motion:
Select an even slower shutter speed, and any motion will be invisible or blend. This is useful for some special use cases, e.g. ‘silky’ water, and ‘invisible’ tourists.
When you have long shutter speeds of maybe 30 seconds, several waves of water would pass before the shutter closes, and the whole motion of each wave would be in the one frame. The result is a silky texture; it looks more like a very calm sea:
The next example shows how you can use a slow shutter speed to get rid of pesty tourists. It is very difficult to let them disappear, as that would require a very long exposure time. You might need a special filter to reduce the available light (a strong neutral density (ND) filter), and the tourists might not move as wanted. So that is a game you most likely lose, but it can still be fun for interesting ghost effects:
You naturally have to use slow shutter speeds for dark environments or night photography, e.g. the popular Milky Way shots. Astro-Photography is a rich topic which deserves its own article.
What else is there to tell you about shutter speed?
Maybe the sound of the shutter. When you click the shutter button, what follows is a symphony of mechanical action inside the camera: the shutter button itself, the mirror (if you still use an SLR camera 🙂 ) flipping out of the way, the aperture blades closing, and the shutter curtains opening and closing again. Some cameras have a very satisfying ‘click’ (photographers call the entire process ‘actuation’) , but some can be very annoying. I was recently in the audience of a musical performance, and the (amateur) photographer didn’t care about the noise pollution she caused by the constant click-click-click thunderstorm, which ruined parts of the performance for the audience. For cases like these, many modern digital cameras have an electronic shutter at their disposal. It is a silent shutter, no ‘click’ at all. It works by turning the sensor on and off for the exposure duration, instead of opening and closing the shutter curtains. Recommended for any situation where the ‘click’ sound is an annoyance.
We should also talk about using a tripod or something else to stabilize the camera when using longer shutter speeds. The longer the exposure time, the more likely it is that any camera shake is visible in the image as a blur. Short shutter speeds freeze not only the motion of the subject but also ‘freeze’ the motion of the photographer, making sure the image is sharp. This is especially important when using lenses with a high magnification (telephoto lens, macro lens), as any camera movement is also more pronounced and requires a shorter shutter speed for acceptable sharpness. Unfortunately, a short shutter speed means you need a lot of light to get the image properly exposed. There is always a trade-off. That makes it challenging to select the best combination of Shutter speed, Aperture and ISO to get a good exposure and also control all the different effects they carry with them.
Have fun taking pictures, maybe try some silky-wave-long-exposure next time?