Like light and composition, the sharpness of a photo can either make it or break it. Naturally, we all want our photos to be maximally sharp, but that’s easier said than done sometimes, especially if you’re holding the camera in your hand.
There are many causes of image blurriness. It could result from simply holding the camera wrong or it could be induced by the mirror locking up. Most commonly, however, image blurriness is the result of using a shutter speed that is simply too slow for holding the camera in your hand.
There is, however, a trick that will help you get sharp photos each and every time, even if you’re hand-holding the camera: the reciprocal rule.
The Reciprocal Rule in a Nutshell
The reciprocal rule states that the shutter speed should be greater than or equal to the reciprocal of your lens’ effective focal length. For example, if you’re shooting with a 70-200mm zoom lens on a full frame camera, at 70mm you should use a shutter speed of 1/70 seconds or faster. At 200mm, a shutter speed of 1/200 seconds or faster is needed to avoid camera shake. It’s that simple.
Essentially, the longer the focal length, the more likely the camera is to succumb to the natural movements of your body. If you’ve got a zoom lens, you’ve undoubtedly noticed that there is a much greater degree of camera shake when you’re zoomed in than when you’re zoomed out. Therefore, using a faster shutter speed is required as the length of the lens becomes greater.
Beware of “Effective Focal Length”
Note that in the explanation of the reciprocal rule, the term “effective focal length” is used. If you shoot with a crop sensor camera, the crop factor will be an important variable in your calculations of the focal length you can use. To determine the shutter speed you can use, you must multiply the crop factor by the focal length. For example, if you use the same 70-200mm lens on a camera with a 1.5x crop factor, you’d need a shutter speed of 1/300 seconds at 200mm (1.5 x 200 = 300). At 70mm on the same 1.5x crop sensor camera, you’d need to use a shutter speed of 1/105 seconds.
Other Variables That Affect Sharpness
Granted, using the reciprocal rule should get you close to the appropriate shutter speed to get a sharp image, but there are plenty of other factors at play that could impact the sharpness you can achieve in a given shot. The quality of the lens you use will certainly determine how sharp the images are, as will the resolution of the camera (higher resolution cameras are much less tolerant of camera shake). How you hold the camera will influence the minimum shutter speed you can use as well, and in turn, impact the sharpness of your images. Even the subject matter you photograph and your distance from it will play a role in choosing the most appropriate shutter speed to obtain maximum sharpness.
In short, the reciprocal rule isn’t a hard and fast rule, but a rule of thumb to get you started. Find the reciprocal of the focal length and be ready to do some fine tuning, if needed. You might find that you need a much faster shutter speed than is recommended by the rule if you’re in one of the situations mentioned above.