Lesson 4: shutter speed, and how it works alongside aperture
It’s time for another blog post following on from my previous discussions on photography basics. As always, this is to celebrate having another handful of photos accepted on Dreamstime. I have now made a massive 42 accepted images, my latest one taken on a worldwide photo walk in Paddington:
So earlier I talked about choosing cameras and available lenses, and I have also mentioned camera apertures and the way in which the size of the aperture (or hole) through which light passes is controlled by a diaphragm, just as the iris controls the size of the pupil in the eye. Put simply, if there’s too much light out there, the amount that hits the camera sensor can be restricted by making the aperture smaller. If there is insufficient light, widening the aperture will increase the amount of light that can enter the camera.
Usually the camera automatically regulates all this so that even in low light conditions as in the photo below, a decent photo is produced:
For me, the aperture control was really the first setting to get to grips with when learning photography.
Modifying the shutter speed is another way in which the camera (or photographer) controls the amount of light that hits the sensor. In this post I want to talk about these shutter speeds and also start to touch on how developing a combined control of shutter speed and aperture can results in much better photography.
When you press the button to take a photo, a mirror inside the camera flips up out of the path of incoming light. Usually light passes through the lens, striking this mirror and finds its way into the view finder. However with the mirror flipped up, light passes straight through onto the sensor and an image is recorded. The length of time during which the mirror is up and the sensor is exposed is controlled by setting the shutter speed. This can be set manually on the camera if need be. It is measured in seconds and fractions of a second.
Again, this controls the amount of light entering the camera. The longer the shutter is open for, the more light will enter.
The amount of light reaching the sensor is called the exposure. If too much light reaches the sensor then a photo is said to be over exposed (it looks too white and washed out). The reverse of this is an under-exposed photo, in which there is too much darkness. In both cases, detail is lost, and the photo is poor.
If the aperture is open too wide and the shutter speed too slow, then the photo will be over exposed.
If the aperture is too small and the shutter speed too fast, then the photos will be under exposed.
It is imnportant to note that the same exposure of a photo could be achieved in two ways:
1. A fast shutter speed and wide aperture
2. A slow shutter speed and a small aperture
I once took my new camera on a climbing trip to the French Alps and took some pretty poor photos and as a result I learnt about too crucial settings: aperture priority (AV) and shutter prioirty (TV). Most of my images were taken in a wooded gorge in low light conditions. I had my camera set to the AV setting or 'aperture priority'. In this setting I can manually adjust the aperture and the camera will automatically compensate for this by changing the shutter speed. I.e. as I make the aperture smaller the camera will set a longer exposure time. For my entire trip through the gorge I had the aperture set to a ridiculous f11 (that’s fairly small) and the shutter speed was set automatically to around 1/20 of a second. The result of this was a shameful album of blurred image because my hands just aren’t that steady.
So what should I have done? I had five options.
1. With the camera still in AV mode, select a wider aperture (e.g. f 2.8). The camera would then compensate by decreasing the shutter speed
2. Change to TV mode and select a faster shutter speed. The camera would then compensate by widening the aperture
3. Change the camera to MV mode in which I could manually set both the aperture and the shutter speed.
4. Use a tripod (which I didn’t have)
5. Take off the polarising filter which I had stupidly put on my lens, which was effectively blocking light and forcing the camera to decrease its shutter speed.
Here's an example of a photo where I succesfully used a fast shutter speed to capture moving water:
So hopefully you can see that by changing one setting, the camera will change the other in order to achieve the ideal exposure for a photo. I have also illustrated a good reason for not leaving your camera in automatic mode. By taking control, you dictate the shutter speed and ensure that you produce nice sharp images. Conversely though, you may deliberately want to blur images by setting a long shutter speed. There are two common examples of this technique. The first is when taking the classic shot of the sky at night, when moving stars blur their
way across the camera sensor to produce concentric circles. The second technique is to capture moving water with a slow shutter speed to yield a silky smooth artistic effect. Many more reasons will come in future blog posts.
Photo credits: Kim Deadman.