In the previous article I talked about how shutter speed affects the exposure of a photo. Please have a look at the post on Exposure Definition.
Have you taken many soft blurry photos? Why does it happen and how we can avoid such undesirable images?
How Do Film Cameras Work?
To explain soft blurry photos, let us first use film cameras as an example. There are a couple of factors that influence the exposure of film:
- Shutter speed: The length of time that the shutter, the mechanism that allows the light in to stay open. Light needs to fall on the film to record an image.
- Aperture: This is the hole behind the lens that funnels the light onto the film. A bigger hole will let in more light, helping to record the image faster. The size of the aperture opening is indicated by your camera with an f-stop. The number you see, for example f/1.8 or f/16, offers information that is a bit counter-intuitive since an f-stop of f/1.8 indicates a bigger aperture opening than f/16.
- ISO: The sensitivity of the film. Very sensitive film can record a picture quicker with less light.
For digital cameras the principle remains (mostly) the same. Where film was exposed in the olden days, a digital sensor is now used to record an image.
The digital camera also introduces an Automatic mode where the in-camera computer tries to solve the problem of over- and underexposure. Auto mode is smart enough to know when a photo is still underexposed, so it will leave, as one of its tricks, the shutter open until an image is exposed just right.
Not Enough Light = Camera Shake Blur
Sometimes when you take a photograph in low light, the Auto mode realizes that not enough light has fallen on the sensor to have a properly exposed image. It therefore leaves the shutter open longer than your hands can hold the camera steady. It will inadvertently record the tiny shake of your hands as well, resulting in a soft or blurry photo as seen below.
This is also known as motion blur or camera shake blur. In the photo above the shake blurs are vertical – my hands moved the camera slightly up and down.
Please note that a shake blur is not the same as an out of focus error. An out of focus error has to do with distance from the camera where the focus point might be on the background and not on your subject situated closer. I will get to out of focus blurs in the next post.
So how do you prevent camera shake in low light? If Auto mode decides to leave the shutter open longer for a proper exposure, the chance is better that the photo will be distorted if the hands holding the camera move slightly. If the shutter can open and close really fast, let’s say faster than 1/500th of a second, even your hands moving will not have a noticeable effect on the photo and your shots ought to be sharp. But at 1/500th of a second, a lot of light will be needed to register on the sensor in a short span of time for you to have a properly exposed image. If there is not enough light around, you will end up with an underexposed image.
Busy Kids = Soft Blurry Photos
If you don’t have enough light, what options remain for the camera? Tiny movements of your hands can cause a soft or blurry photo. But if the subject (whom you are trying to photograph) moves, even if your hands are steady, you can also end up with a motion blur. I have many photographs of blurry kids running around in low light conditions.
Creative Effects Using Camera Shake
Motion blurs can be used to good effect. Have a look at the next shot where the bride’s face is sharp and everybody else is blurred out.
If we open the aperture wider and flood the sensor with more light, we will expose the photo correctly quicker. This means a faster shutter speed can be achieved that will lead to sharper photos and less blurry kids. So is it good to take all photos with a wide open aperture? Sure it can solve the camera shake problem. But now you run the risk of taking out of focus shots, as a wider aperture leads to a shallower depth of field.
Please see our next article on “Deep or shallow depth of field” for a simple explanation.