The Reciprocal Rule

As it relates to sharp photos, good hand-held technique is where it all starts. But there are other tips and tricks you can use in conjunction with good technique to help ensure your photos come out clear and sharp. One such tip is known as the Reciprocal Rule.

The Reciprocal Rule is an easy-to-use guideline for hand-held shooting that you can use to figure out what shutter speed you need to use to effectively eliminate camera shake. The Reciprocal Rule is as follows:

For any given focal length, you want to use a shutter speed that is the reciprocal of that focal length, or faster.

We think of fractions as parts of numbers, but even whole numbers are fractions. For those who remember their 4th grade math, the number on top of a fraction is the numerator, the number on the bottom of a fraction is the denominator, and to get the reciprocal, you simply flip the fraction upside down, putting the denominator on top and the numerator on the bottom. For example, 30 can also be stated as a fraction as 30/1.   The reciprocal of 30 is then easily shown as 1/30. So for a focal length of 100, the reciprocal of that would be 1/100. And so on.

How do we apply this to photography? If you’re using a 50mm lens, you would want to make sure the shutter speed is 1/50 or faster to effectively eliminate camera shake from your images. If you’re using a 200mm lens, you would want to make sure the shutter speed is 1/200 or faster to effectively eliminate camera shake. And so on…

If you do some quick calculations in your head, you’ll realize that this will allow you to use slower shutter speeds for wide-angle lenses. Conversely, you’d need to use faster shutter speeds for telephoto lenses. Camera shake becomes more noticeable as you use longer and longer focal length lenses, or as you zoom in on a subject using a zoom lens (which is using the longer focal lengths of a zoom lens), so it makes sense that you would need to minimize the time the shutter is open during the exposure while shooting with a longer focal length lens.

There are some important caveats to consider regarding the Reciprocal Rule:

  1. The “Rule” is more of a guideline, and is not one-size-fits-all. Some people have shaky hands, or poor technique. The Reciprocal Rule is simply a baseline to give you a “ballpark estimate” of what shutter speed you would need to use. Some people with shaky hands would need to use a shutter speed faster than the rule recommends. People with steady hands and good technique might be able to get away with slightly slower shutter speeds. Start with the recommendation of the rule, and adjust for your personal style as needed.
  2. If you are using a camera with a sensor that is smaller than a full 35mm frame, you need to multiply the focal length of the lens by the sensor’s crop factor or multiplier to figure out the effective 35mm focal length, and use the reciprocal of the effective focal length. If you don’t know if your camera has a full frame sensor, then it likely doesn’t. Cameras that have smaller-than-full-frame sensors include:
    • Most Nikon DSLRs, except the D700D800, and their D3 series and D4 series
    • Most Canon DSLRs, except the EOS 5D series, 1Dx, and 1Ds series
    • almost every point-and-shoot camera in existence
    • every cameraphone you’ve ever used

    So, for example, if you’re using a 200mm lens on a Nikon camera with an APS-C sensor, which has a 1.5x crop factor, your effective focal length becomes 200 x 1.5 = 300mm, so you would need to use the reciprocal of 300, which would be a shutter speed of 1/300 or faster.

For quick reference, here are some of the most common crop factors:

  • APS-C (Nikon DX, Pentax, and Sony) – 1.5x
  • Canon APS-C (Most Canon DSLR models) – 1.6x
  • Micro 4/3 – 2x
  • 1/2.5” (Most point-and-shoot cameras) – 6.02x
  • 1/3.2” (iPhone 4S) – 7.61x

One final note, in case it wasn’t obvious… the Reciprocal Rule is only meant as a guideline for hand-held shooting. If you’re using a tripod, shutter speed doesn’t matter. Since a tripod is perfectly stationary, all photos taken with one should come out perfectly sharp since there is no camera shake.

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