The post The Reciprocal Rule in Photography, Explained appeared first on Digital Photography School. It was authored by Adam Welch.
If you’ve ever come back after an exciting photoshoot, only to find that some (or all) of your images are frustratingly soft, then you might be dealing with a common problem: blur due to camera shake.
In other words, your camera’s shutter speed was too slow, so every time your hands moved (even slightly!), blur was introduced into the frame.
But even once you recognize the problem, you still have another question to ponder: How fast do you need to set the shutter speed to avoid blur due to camera shake?
Now, the technical answer is that you can’t easily determine the ideal shutter speed for handholding your camera. It depends on a variety of factors, including the subject’s level of magnification, the lens’s focal length, the steadiness of your hands, the weather, and more.
Fortunately, photographers have developed a handy guideline – known as the reciprocal rule – that’ll help you bypass all the complex factors that go into determining the perfect shutter speed, and quickly estimate a good shutter speed setting on the spot.
But what is the reciprocal rule? How does it work? And how is it affected by crop factors and image stabilization? In this article, I explain everything you need to know about the reciprocal rule in photography. And by the time you’re done, you’ll know how to apply it for consistently sharp shots.
Let’s get started.
What is the reciprocal rule in photography?
The reciprocal rule states that your shutter speed should always be at least the reciprocal of your lens focal length – that is, “1” over the focal length (or faster). Otherwise, you’re at risk of blur due to camera shake.
So if you use a 50mm lens, you’ll need a shutter speed of at least 1/50s. If you use a 200mm lens, you’ll need a shutter speed of at least 1/200s. And if you use an 800mm lens, you’ll need a shutter speed of at least 1/800s. Make sense?
According to the reciprocal rule, as long as you set your shutter speed to the calculated value or faster, you can capture sharp handheld shots.
But the reciprocal rule does come with several qualifications, which you should always bear in mind:
- It applies to full-frame cameras, not APS-C cameras (if you’re using an APS-C camera, you’ll need to adjust the equation, as I discuss below!)
- You must be shooting with good handholding technique and low wind
- 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
Note that the reciprocal rule, despite its name, is not really a rule. It’s a guideline, an easy way to stop handheld-induced camera shake from ruining your photos. There are certain situations when you can ignore the reciprocal rule, or you can adjust the reciprocal rule to get good results (more on that later!).
Why does the reciprocal rule work?
The reciprocal rule is all about preventing handheld camera shake from ruining your images. You see, when you work handheld, camera shake is a fact of life – but use a fast-enough shutter speed, and any camera shake will be negated by your split-second shutter.
But why does focal length make a difference? Why doesn’t every lens have the same “fast-enough” shutter speed?
Longer focal lengths have a more constrained field of view. In other words, longer focal lengths magnify the world, thereby amplifying camera shake.
So when you shoot at 50mm, a little camera shake isn’t such a big deal. But zoom out to 600mm, and even the slightest movement becomes a problem. As a result, you must increase your shutter speed to compensate.
If you’re struggling to understand this concept, then check out my video, where I explain why the reciprocal rule works (using visuals!):
Bottom line: The goal of the reciprocal rule is to increase your shutter speed as the focal length gets longer, thereby counteracting the decreased field of view and its potential to magnify camera shake.
However, the reciprocal rule does depend on certain conditions, which I dive into below:
The reciprocal rule and body stability
The reciprocal rule assumes your body is relatively stable; it also assumes that you’re using decent camera handholding technique. So it doesn’t apply if you’re standing on one leg, jumping up and down, climbing in a tree, or otherwise imbalanced.
Instead, for the reciprocal rule to work, you should be standing with your knees slightly bent, both hands holding your camera, and your elbows tucked close to your side or chest. I’d also recommend using your camera’s viewfinder, not the LCD screen; using the LCD screen to compose will cause your arms to go out, destabilizing the camera as a result.
External factors can affect body and camera stability, too. If you’re shivering due to the cold, or you’re being blown this way and that due to high winds, then the reciprocal rule will give you a too-slow shutter speed.
Therefore, I recommend you increase your shutter speed past the reciprocal rule if you’re:
- Imbalanced
- Working in wind
- Holding your camera away from your face
It’s impossible to give an exact recommendation for how much you should boost your shutter speed in these scenarios, so I’d suggest you do a few tests. Take some photos while using the LCD screen, take some photos while poorly balanced, and so on. Work at different shutter speeds and check the results. Then develop a modified reciprocal rule for each scenario.
Happily, certain scenarios allow you to relax the reciprocal rule. If you’re able to gain extra stability by leaning against a solid surface (such as a tree or a brick wall), then you can drop the shutter speed past the reciprocal rule’s “allowed” value. You can also drop your shutter speed when shooting from a kneeling position, you can drop it even further when lying on the ground, etc.
Sensor size and the reciprocal rule
As stated above, the reciprocal rule only applies to full-frame sensors. Smaller sensors, such as APS-C and Four Thirds sensors, crop the focal length (the same way that you can crop a photo in post-processing).
This magnifies the image, and hence the blur due to camera shake.
When discussing APS-C and Four Thirds cameras, you’ll often hear about crop factors. These allow you to determine your lens’s effective focal length or focal length equivalent; you just multiply the actual focal length by the crop factor.
So if your camera has a 2x crop factor and you’re shooting with a 100mm lens, you simply multiply 100 by 2 for a 200mm effective focal length.
And it’s this effective focal length that you should use with the reciprocal rule.
In other words, to apply the reciprocal rule to cropped sensors, you must first determine the effective focal length of your lens, then calculate your shutter speed minimum via the reciprocal rule.
If you’re not certain of your camera’s crop, you can always do a quick online search, but here are some 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
Also, while I don’t want to make things too complicated, know that you must do the same when using sensor sizes larger than the full-frame standard – but you’ll use a reverse crop factor (such as 0.8x, 0.5x, etc.). Medium- and large-format cameras feature wider fields of view, increasing the duration of your allowable handheld shutter speed.
The effects of image stabilization
Some cameras and lenses offer image stabilization, which helps counteract handheld camera shake.
As you can probably guess, this means that you can use a slower shutter speed than the value recommended by the reciprocal rule – but how slow can you go?
Image-stabilized cameras and lenses come with a reported stabilization value – you can find this in the manufacturer spec pages, but it’s generally in the area of three to five stops on older gear, and four to seven stops on newer gear, especially when a stabilized camera and a stabilized lens are used together.
You can use this stabilization value to calculate a modified reciprocal rule.
Simply identify your reciprocal rule shutter speed, then reduce it by the required number of stops.
(Stops are a way to talk about changes in exposure variables; a single stop corresponds to a doubling or a halving of your shutter speed value.)
That said, if you want a more accurate guideline, you should test each lens and camera. Take a series of shots while reducing the shutter speed. See how low you can take the shutter speed while still producing sharp photos, then commit the number to memory.
The reciprocal rule and macro lenses
Earlier in this article, I explained that the reciprocal rule works because it accounts for how camera shake is magnified by longer lenses.
And this is largely true – but what the reciprocal rule doesn’t take into account is the increased magnification that comes from getting close to your subject. In macro photography, for instance, you’ll often use a relatively short lens (e.g., 100mm), yet you’ll shoot at 1x magnifications. The reciprocal rule will suggest that you use a shutter speed of, say, 1/100s, yet in most scenarios, that just won’t be enough (assuming you’re handholding your setup, that is; if you’re using a tripod, then you can ignore this completely!).
My recommendation, then, is to add a stop or so to the reciprocal rule as you get very close to your subject. If you’re photographing at 1x magnifications – or even near-1x magnifications – you’ll want to boost the shutter speed a tad, just to be safe.
Of course, for the best results, it’s always a good idea to capture a few shots at slightly different shutter speeds, but a modified reciprocal rule should act as a great starting point.
When the reciprocal rule fails
The reciprocal rule is a useful method for calculating shutter speed minimums. And as you’ve seen, you can modify the reciprocal rule to deal with crop-sensor cameras, image stabilization, and more.
But there are a few situations in which the reciprocal rule fails completely – so completely, in fact, that you’ll need to ditch the rule and think in different terms.
Shooting with a tripod
A good tripod stabilizes your camera so completely that you can drop your shutter speed as much as you want and you’ll still capture a sharp shot.
In other words, if you’re working with a tripod, you can forget about camera shake, you can forget about the reciprocal rule, and you can just lengthen your shutter speed until you get the result you’re after.
Of course, you must be using a solid tripod and it must be set up on stable ground. You’ll also need to use a two-second self-timer or a remote release to prevent mechanical camera shake, and you’ll need to make sure that your subject isn’t moving.
But as long as you use proper technique and a sturdy tripod, and as long as you photograph a stationary subject, you’ll capture crisp images no matter your shutter speed.
Shooting action
The reciprocal rule is designed to prevent blur due to camera shake. Unfortunately, that does not extend to blur caused by moving subjects, such as people walking, cars racing, or birds flying.
Which means that, when you’re capturing action, you’ll need to use a shutter speed far higher than the reciprocal rule suggests.
The specifics depend on the subject, but I’d recommend starting at 1/250s for slow-moving subjects, 1/1000s for fast-moving subjects, and 1/2000s for very fast subjects (such as birds in flight). Note that you’ll still want to increase your shutter speed as you increase your lens’s focal length, but the reciprocal rule itself will be largely useless.
Shooting with strobes
When you’re using strobes of any kind – whether speedlights or studio strobes – you’ll need to ignore the reciprocal rule completely (assuming that your subject is completely lit by the strobes, and not by the ambient light). Instead, you’ll generally want to set your shutter speed to your camera’s flash sync speed (generally around 1/200s or so).
And here’s why:
Strobes are fast enough that they make your camera’s shutter speed setting redundant. If your strobe flashes at 1/20,000s, for instance, it won’t matter whether your camera is set to shoot at 1/200s or 1/60s; the burst of light from the strobe will freeze the subject, even if your camera shakes during the exposure.
The reciprocal rule in photography: final words
The reciprocal rule is a handy guideline for keeping your shots sharp – and while it’s far from perfect, I certainly encourage you to use it whenever you’re struggling to determine the right shutter speed!
So the next time you’re working handheld, try the reciprocal rule. See if it nets you sharp photos.
(And then do some testing for your own modified reciprocal rules!)
Now over to you:
Have you been using the reciprocal rule in your photography? Do you plan to start? Share your thoughts in the comments below!
The post The Reciprocal Rule in Photography, Explained appeared first on Digital Photography School. It was authored by Adam Welch.
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