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Reciprocal Rule featured image.

Are you having blurry images with your handheld photos? Chances are, you are not using the fast enough shutter speed to reduce blur from camera shake when shooting handheld.

An easy trick is to apply to reciprocal rule when choosing the most appropriate shutter speed for your image. It is a popular hand-holding rule of thumb to keep images nice and sharp.

What is the reciprocal rule in photography?

The reciprocal rule defines the slowest shutter speed you can use to avoid camera shake blur on a given focal length when shooting handheld.

To apply it, use a shutter speed equal to or greater than the reciprocal of your lens’ effective focal length.

For example, if you are using a lens at 50mm, then the “safe” shutter speed is 1/50th of a second or faster. Going below it may give create blur due to camera shake.

Image comparison of photos following the reciprocal rule vs using slower shutter speed, not following the rule.

The image above shows what might happen if you use a shutter speed setting that is too slow for your focal length.

However, you can use a slower exposure time than what is recommended by the reciprocal rule if you got an excellent camera hand-holding technique.

So rather than a rule, it serves more like a rough guideline as sharpness is subjective in the first place. Nonetheless, it is a very easy trick to remember if you do not know which shutter speed you should be using.

Note: Focal length does not affect the actual amount of camera shake. But longer ones make every little movement more noticeable.

You may think that you’re holding the camera completely still. But in your camera’s perspective, things like breathing or any slight movements are intensified at longer focal lengths.

So the longer the focal length, the faster the shutter speed you want to use if you do not have any sort of stabilization.

However, the example above is only applicable for a full frame camera…

Applying the rule of reciprocal on crop sensors:

When trying to apply the reciprocal rule on crop sensors, we must first get the effective focal length.

The thing is, the guide is a rule of thumb based on a 35mm sensor size (full frame).

If you’re just starting out, you probably have an APS-C or a micro four-thirds camera body, which has a sensor size smaller than a full frame camera.

Focal length affects the field of view, and in a way, sensor size too, in the form of the crop factor.

I will not go into the nitty-gritty of this term in this article but I’ll give you the gist:

Why you should multiply the focal length by the crop factor when getting the reciprocal rule.

Basically, smaller sensors only capture a smaller portion of an image compared to bigger sensors. This makes a 25mm lens looks like a 50mm lens on a micro four-thirds camera in terms of field of view.

As a result, it intensifies any micro-movements within a frame, creating more camera shake blur than that of a bigger sensor.

Therefore, the “safe shutter speed” for a 50mm lens on a full frame camera is not the same on a crop sensor camera with the same focal length.

How to Calculate the Effective Focal Length:

Getting the effective focal length is not hard. You just need to multiply the focal length by the crop factor.

Here are the most common crop factors and their effective focal length calculations:

EF is Effective Focal Length
f is Focal Length

  • Full Frame (1x crop factor) – EF = f x 1
  • Nikon DX (1.5x crop factor) – EF = f x 1.5
  • Canon APS-C (1.6x crop factor) – EF = f x 1.6
  • Micro Four Thirds (2x crop factor) – EF = f x 2

Once you know the effective focal length, you can then apply the rule of reciprocal.

If the answer turns out not available as a shutter speed option, just round up to the nearest available setting.

Here’s a chart showing examples of the most commonly used focal lengths and their recommended shutter speed setting based on the reciprocal rule.

Reciprocal Rule chart for the most common focal lengths used based on a full frame field of view.

Note: Some shutter speed settings only appear if you set the increment on 1/3 or 1/2 stops. To see the list of settings available at each increment, check out this link.

Key differences between Motion Blur vs Camera Shake Blur:

You have to remember that the reciprocal rule tries to solve the issue of camera shake blur, not motion blur.

Knowing the difference between these two will give us an idea of what the rule can, and cannot do to improve your image.

First off, motion blur may appear only on some portion of your image while camera shake can affect the whole image.

Check out this photo of a drone.

Flying Drone showing motion blur on the rotor blades.

The blurriness you see only happens at the drone’s rotor blade but the rest is nice and sharp.

Unlike camera shake blur, motion blur can show up to your image as long as the subject’s movement is faster than your current shutter speed.

For example, you are shooting at a 50mm using 1/50th shutter speed but you are shooting a car running at 150 mph.

Yes, you probably reduce the camera shake blur. But you’ll certainly have a lot of blurs around or even the car itself.

This is due to the car’s speed of motion being faster than a 1/50 shutter speed can freeze. In other words, the car probably moved a few distances in the span of 1/50th of a second.

Reciprocal Rule and Image Stabilization:

Image stabilization is a special feature added in lenses or cameras that helps reduce camera shake.

With lens or camera image stabilization, you can use slower shutter speed than you’d typically use with the reciprocal rule.

Take a look at the image comparison below. I used a 200 mm lens and a shutter speed way slower than what I’d normally use. All this while trying really hard to keep my hands steady.

Comparison of photos taken with lens image stabilization turned on vs. turned off.

Image stabilization usually helps reduce camera shake by around 2-4 stops.

Say we are using a 100mm lens on a full frame camera. The reciprocal rule states that the minimum shutter speed we should use is 1/100th of a second.

With a 2 stops image stabilized lens, we can shoot at 1/25th before camera shake becomes apparent.

Keep in mind though that it only helps reduce camera shake.

The amount of light gathered is still the same. And motion blurs will still be apparent if there is something moving inside your frame faster than your shutter speed.

It is also not a replacement of tripods for long exposure shots.

Does this feature render the knowledge of reciprocal rule useless? In my opinion, no.

It will at least give you an idea on how far you can push your shutter speed even with the image stabilization turned on.

Some Exceptions:

Have you noticed why I always include a double quotation on the word “safe”?

The rule of reciprocal works most of the time but it is not absolute and should only be used as a guideline.

You may have to use faster shutter speed than what was suggested depending on a few other variables.

Other than image stabilization, here are some more instances where the reciprocal rule may not be applicable:

  • Focal length shorter than 50mm – When you go at a shutter speed slower than 1/50th of a second, the motion blur and camera shake can almost always appear if you have a poor handheld technique.

    For this reason, just stick with 1/50th for focal length less than 50mm. At least until you improve your handheld technique.

    Keep in mind that motion blur may still be apparent even with excellent camera hand-holding.

  • Handheld Technique – You may have to use faster shutter speed if your hand is a little too shaky when shooting handheld.

    Conversely, you can also away with a slower shutter speed if you got an excellent handheld technique. At least on the shorter end of the focal lengths.

  • The print size and Camera Resolution – Technically, cameras with very high resolution will more likely keep minor movements on a pixel level.

    If you are uploading your image on the web like for Instagram for example, the resolution shouldn’t be an issue.

    The difference isn’t that great when viewed at the same magnification, in other words, normal view. In this scenario, this only makes sense when pixel peeping.

    It does, however, matters if you are planning to print a big image out of it.

    In this regards though, it would be better to use a tripod and have a higher resolution camera. Simply because enlargement plays a bigger role in sharpness when it comes to printing large sized images.

    Nevertheless, you may have to use faster shutter speed than the reciprocal rule for higher resolution cameras and print size. At least when shooting handheld.

  • Fast Moving subjects – As pointed out earlier, camera shake blur is different from motion blur. The rule of reciprocal won’t help you get a sharp shot of those moving subjects.

    So when photographing a fast moving subject, your shutter speed should match the subject’s speed. That is if you plan to get a freeze motion shot instead of showing motion blur.

Conclusion:

The reciprocal rule a very helpful guideline you can use to reduce blur due to camera shake when shooting handheld.

Using a tripod is by far a more reliable solution to reduce camera shake, but there are a lot of situations where we can’t use it.

And even with optical stabilization, knowing about the rule actually gives us a clear understanding of how to better use the feature.

Did we miss something? Leave a comment below and we might just add it to this guide.

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