How can I make my photos sharp? - Part 2: Shutter Speed Rule of Sum

As we all know that shutter speed plays an important role in the sharpness of the photos. Moving subjects require much higher shutter speed than still subjects. However, most people probably don't know that how fast shutter speed an image needs also depends on focal length (how much you zoom in), direction of the movement of a moving subject, how close you are to the subject, if you can hold the camera steady and if you have a lens with a image stabilization built in. I know, there are a lot to think about before you press the shutter!

To keep things simple, we are going to assume that you have a child posing for you at 7 feet away as shown in the image above. We also are going to assume that you are using a 50 mm prime lens without image stabilization built in. In this case, you would want to have the shutter speed to be 1/50 second or faster. If you have a long lens and you zoom in at 125 mm, you would want to use a shutter speed of 1/125 second or faster.

You see, the rule of sum is that the shutter speed is best to be faster than 1/focal length.

The more you zoom in, the higher shutter speed you need.

In bright sunlight, shutter speed is normally not a problem. But in the low light situation, you may have to adjust the aperture and/or ISO to increase the shutter speed. In other cases, you may want to use tri-pod or flash. We will talk about these in later posts.