Now that we have been able to achieve autofocus on our subject and have selected the correct aperture to ensure that the we render our subject sharp and in focus, there is really only one other variable in the equation that can go wrong.
Quite simply, shutter speed refers to the duration that the shutter/mirror inside the camera locks up and allows light to pass through the lens (and your resultant aperture created by your F stop value) and onto the camera’s sensor. Here’s and example of what happens when you compose and then trip the shutter mechanism by taking the image.
This time or shutter speed is typically only a fraction of a second, sometimes as fast as 1/8000th of a second.
Our first goal with shutter speed is to ensure that we have a shutter speed value which is fast enough to eliminate the chance of our image being soft as a result of movement on our part. This is referred to as camera shake and is very often reason why many images may be soft and “out of focus”.
Your focus may have actually been spot on but there was movement of the camera which result in the image not being rendered as sharp as you would like. A general guideline is that your shutter speed should be at least one over your focal length in order to eliminate any chance of camera shake.
If you’re on a full frame camera (more about full frame and crop sensors later but stay with me for now) at a focal length of 300mm your shutter speed should be at least 1/300th of a second to eliminate camera shake. The greater your focal length value (or zoom) the greater potential their is for movement and camera shake. Every extra bit of focal length just amplifies the slightest of movements originating from the camera body.
The second goal with shutter speed is to ensure that the shutter speed is fast enough to freeze or negate any movement in our subject so that it may result in the final image being as sharp as possible despite the movement.
Larger, slower subjects will not need as fast a shutter speed as smaller, fast moving subjects in order to freeze movement.
Similarly, a relaxed leopard lazing around in a Marula Tree won’t require a very fast shutter speed as there is almost no movement.
Is it all about Fast Shutter Speeds?
Not at all. Most of the time we are wanting to capture our subjects without any movement (either asa result of camera shake or their movement in the frame). However, this is not always the case and using a slower shutter speed to intentionally capture movement in a scene makes for interesting results.
The combination of slow shutter speeds and intentional camera movement is, for me, the closest we can get to actually painting with light.
Panning with a moving subject is the most common form of intentional camera movement and allows the photographer to convey a sense of movement in an image.
How Does the Camera Decide on a Shutter Speed
Assuming we are still in Aperture Priority (AV or A) the camera will, after you have dialled in your preferred aperture value, evaluate the scene and will decide on an appropriate shutter speed. Think of this as the Goldilocks effect. The shutter speed that the camera uses is not random but rather based on evaluating the entire scene complete with its dark areas and bright areas and then deciding on a value which ensure that just the right amount of light is let through.
Too much light (too long or slow a shutter speed) and the image becomes too bright or Overexposed.
Too little light (too fast a shutter speed) and the image becomes too dark or Underexposed.
Just the right amount of light and we should have some detail in the shadow areas, the bright areas and the mid-tones (the region between dark and bright).
It makes sense then that in the early morning, late afternoon and at night, the camera gives you VERY slow shutter speeds. There such little light available (even if you’re shooting at your maximum aperture) that the camera has to use a slow shutter speed in order to allow enough light onto the sensor so that you can actually create an image.
This is why so many images taken at school concerts or on a night drive come our horribly blurred and soft.
But What if I Want to Take A Photo In Low Light?
Taking photographs in low light is tricky for most beginners. However, it is actually possible to capture a sharp image in low light and you have a couple of options available to you:
- Keep the camera and your subject VERY still. Not ideal for wildlife photography
- Use a flash.
- Increase your shutter speed.
How Can Increase the Shutter Speed?
That’s where ISO comes in and that will be the topic for our next post in the series.
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