Have you ever heard of the rule of reciprocity in photography? Well, this is another one of those technical rules that can, and, help us get sharper photos, which usually is the goal of any photographer.
As we already know, the photo is a set of many abilities that combined between them, and not necessarily all the same time, allows specific results and specific situations.
Do not confuse the triangle of exposure settings, i.e. how to work our photometry regulating speed, aperture , and ISO, with the rule of reciprocity, even if the triangle requires that every time you fit one of the three elements of the other two (usually) must also be set, mathematically the rule of reciprocity is related to a reciprocal number.
And what is a reciprocal number? The reciprocal of a number is the multiplicative inverse of the number or, in other words, divided by the number 1. For example, the reciprocal of 100 is 1/100.
Got that straightened out, I would like to make a simple analogy to understand why the rule of reciprocity can be useful to get sharper pictures when photographed, mainly, with lenses or zoom teles, where image stability is crucial for good results. Imagine showing a reason through a pvc pipe 1 metre or so. You can toggle your arms, hold your breath and get good results, now try the same thing with a pipe of 3 meters long, what will occur is that he envergará and property you stay, it will be rocking. That’s exactly what happens with our lenses.
Explained that, let’s go to the article that I translated the American photographer Nasim Mansurov which I believe to be the most complete for you learn how to use the rule of reciprocity in the photo, and as you already know, I made the adjustments I needed to facilitate your understanding. Come on?
What is the rule of reciprocity in the picture?
One of the biggest challenges that many photographers face is to take sharp photos when they’re holding a camera with your hands. Many end up with blurry images, without understanding the source of the problem, which is usually the camera movement. Unfortunately, the camera movement can come from many different sources-inadequate support techniques to vibrations of the mirror and shutter that can be really challenging and sometimes impossible to deal with. Although I speak about topics in separate articles, I would like to talk about the most common cause of the movement of the camera: shutter speed less than acceptable when you are holding a camera manually. I will introduce and explain the rule of reciprocity, which can help to greatly increase your chances to get sharp photos when you don’t have a tripod around.
What is the rule of reciprocity?
Due to the fact that we humans we can’t be completely immobile, especially when we’re holding an object, such as a camera, the movements caused by our body can move the camera and introduce a blur the images. The basic premise of the Reciprocity Rule is that your camera’s shutter speed should be at least reciprocal to the effectiveness of the focal length of the lens. If you are confused about what this means, don’t worry – it is easy to understand once you see in an example.
Let’s say you’re shooting with a zoom lens like the Nikkor 80-400 mm f/4.5-5.6 G VR on a Full Frame camera such as the Nikon D750. All the rule is saying is that if you are photographing the 80 mm, the shutter speed should be at least 1/80, whereas if you zoom in to 400 mm, the shutter speed should be at least 1/400.
Use high speeds should prevent blur caused by camera movement. Why? Because there is a direct correlation between the focal length and camera movement-the longer the focal length, the more potential there for the camera movement. If you have zoom lenses like the 80-400 mm lens mentioned above, you’ve probably noticed how your display is more shaky when you look with the zoom in greater focal length, compared with the smaller-that’s because the camera movement is magnified to larger focal lengths:
You can see how the potential for movement of the camera is increased with increasing focal length. The red dotted lines represent the potential limit of how much the camera can move when handled manually, and has limits much smaller than 400 mm to 80 mm. This is because the camera movement is expanded with the increase in focal length.
The camera movement is not the motion blur
It is important to highlight that the blur caused by camera movement is quite different from the motion blur (when the reason is faster than the shutter speed- Panning) – he usually leaves the picture blurred, while the motion blur may just be the reason, or a portion of the grounds blurred, while the rest of the image appears sharp. It is also important to note that the rule of reciprocity only applies when you are holding a camera manually-mount your camera on a stable object, such as a tripod, not will require higher shutter speeds.
Effective Focal Length
Please note that I used the words “effective focal length” in the definition, and provided an example with a Full Frame camera. If you have a camera with a sensor smaller than 35 mm, i.e. a cropada camera (and most DSLRs, semipro camera input and mirrorless cameras have smaller sensors), you first need to compute the effective focal length, also known as “field of view equivalent”, by multiplying the focal length by the crop factor. So, if you use the same 80-400 mm lens on a DX Nikon camera with a crop factor of 1.5 x and is photographing the 400 mm, your minimum shutter speed should be at least 1/600 SEC (400 x 1.5 = 600).
Notes and Exceptions
Although she is commonly called the “rule of Reciprocity”, it is not a rule in itself – just a Guide for the minimum shutter speed to prevent blur caused by camera movement. In fact, as the shutter speed affects the movement of the camera depends on different variables, including:
The efficiency of your handling technique: If you have a bad handling technique, the rule of reciprocity may not work for you, and you may need to use higher shutter speeds. The equipment and lenses range in size, weight and volume, so you may need to use specialized handling techniques, depending on what you’re shooting. Know how to hold the camera correctly, can be crucial to good results, always!
Camera resolution: whether you like it or not, digital cameras are increasing in resolution and as we have seen in the case of high resolution cameras like the Nikon D810, have more pixels in the same physical space clusters can have a drastic effect on the sharpness of images with zoom 100%. Cameras with higher resolutions will show more intolerance to camera shake than cameras with lower resolution. So, if you are dealing with a high-resolution camera, you may need to increase your shutter speed to a value greater than the rule of reciprocity suggests.
Quality/sharpness of the lens: you can have a high resolution camera, but if she is not equipped with a high-performance lens with good sharpness, you will not be able to take sharp photos, no matter how fast shutter speed.
Motive size and distance: shooting a small bird from a long distance and want every detail to be preserved feathers usually requires a longer shutter speed than recommended by the rule of reciprocity, particularly if the reason need to stay sharp with 100% zoom (pixel level).
Image stabilization: this is an important factor and must be explained separately – see below.
The rule of reciprocity stay out if your lens or camera comes with image stabilization (also known as “vibration reduction” or “vibration compensation”), because it reduces effectively the movement of the camera by moving the internal components of the lens or the sensor of the camera. As the implementation and effectiveness of image stabilization depends on several factors, including the technology manufacturer, lens stabilization versus camera image, stabilisation technology efficiency and other factors, your impact varies widely from camera to camera and lens to lens. For example, the Nikon and Canon use lens stabilization and usually claim to have of 2-4 times the potential for offsetting on the lenses, while Olympus claims to have 5 times the compensation in your mirrorless camera OM-D and-M1 with image stabilization system in the body with 5 axes. This is a great potential to reduce the shutter speed to much smaller numbers than the rule of reciprocity would recommend.
In the above example with the lens Nikkor 80-400 mm f/4.5-5.6 G VR, as the lens comes with image stabilization and Nikon claims to have up to 4 stops of compensation, you could theoretically reduce the recommended shutter speed by the rule of reciprocity in up to 16 times. Then, when you’re photographing the 400 mm, if your handling technique is perfect and you connect the image stabilisation, you could go from 1/400 to second (rule of reciprocity based on a Full Frame camera) for 1/25 of a second and still be able to capture a sharp image of your reason (since your reason don’t move at speeds so high and cause motion blurs). In such cases, the Reciprocity rule simply does not apply.
Applying the rule of reciprocity: Auto-ISO
Many modern digital cameras come with a great feature called “Auto-ISO”, which allows you to let the camera control ISO, depending on lighting conditions. Some implementations of ISO are very simplistic, allowing the user to specify only the minimum and maximum ISO and leaving little or no control over the minimum shutter speed. Others have more advanced Automatic ISO capabilities, enabling you to specify not only the boundaries, but also the minimum shutter speed before the ISO be changed. The Nikon and Canon, for example, have one of the best Auto ISO in its modern DSLRs – besides the mentioned above, the minimum shutter speed can be set to “auto”, which will automatically configure the shutter speed based on the rule of Reciprocity:
You can even customize this behavior by decreasing or increasing the minimum shutter speed on the Rule of reciprocity. For example, on my Nikon D750, I can configure the minimum shutter speed to “auto”, then set the limit to “Faster”, which will double the shutter speed based on the Rule of reciprocity. So, if I’m photographing the say, a focal length of 100 mm, the camera will automatically increase the ISO only when my shutter speed falls below 1/200. And if I use a stabilized lens and want my camera has a minimum shutter speed lower, I can move the limit to “slow down”, reducing the minimum shutter speed according to the rule of reciprocity.
Many times all we need is to surround himself with simple tips and techniques to be able to move forward in our photographic journey, it is important to consider that a good equipment does not get good results by itself, you have to devote to learning the basics of photo consistently and always achieve the results we desire. I hope I have contributed this article to you climb another rung on your photographic journey.
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