What is Reciprocal Rule & How to Use it

What is the reciprocal rule in photography?

The reciprocal rule states that to capture sharp photos, your shutter speed should be at least “1” over your lens focal length. In other words, to keep your shots sharp, you should use a shutter speed that is the reciprocal of your lens, otherwise, you’re at risk of blur due to camera shake.

As an example, using a 50mm lens, you’ll need a shutter speed of at least 1/50s. And if you use a 200mm lens, you’ll need a shutter speed of at least 1/200s.

The reciprocal rule comes with several qualifications:

  • It applies to full-frame cameras, but you can calculate the rule for crop sensor cameras
  • It’s designed purely for handholding; if you’re using a tripod, you can work at far slower shutter speeds than the reciprocal rule suggests

Sensor size and the reciprocal rule

The reciprocal rule only applies to full-frame sensors. Smaller sensors, such as APS-C and Four Thirds sensors, crop the focal length.

And it’s your effective focal length that you should use with the reciprocal rule.

Common factors:

  • Canon APS-C: 1.6x
  • Nikon APS-C: 1.5x
  • Fujifilm APS-C: 1.5x
  • Sony APS-C: 1.5x
  • Four Thirds/Micro Four Thirds: 2x

So the next time you’re working handheld, try the reciprocal rule to get sharp photos.