Shifting from Auto mode to Manual mode can be unnerving, especially if you’re not fully aware of the functions pertaining to each of the exposure settings. As this article explains the concept of the reciprocity law in Manual mode, we hope that it’ll help you master the stops compensation-relationship between the ISO, shutter speed and aperture and apply it to your daily photography shoots seamlessly. To refresh your memory on the exposure triangle, let’s first dive into the three key available settings.
Aperture
Aperture is defined by the opening in a camera lens where light passes to enter. A large aperture produces images with a shallower depth of field, gradient blur and allows more light to enter (example as seen above on the left). Smaller aperture allows less light to be captured, less gradient blur and a deeper depth of field.
Shutter Speed
Shutter speed refers to how fast your camera shutter closes when taking a photo. A slow shutter speed allows for more light to be captured, which will brighten up the output but will blur the motion of your subject (provided they are moving). A fast shutter speed freezes the subject in motion, reduces camera shake but allows less light to be captured.
ISO
ISO refers to the graininess and the sensitivity of your camera to light. A low ISO value produces less noise in the image and has a lower sensitivity to light. A higher ISO value produces more visible noise and has higher sensitivity to light.
Reciprocity Law
To put it simply, the reciprocity law is essentially the act of compensating an equal - or close to equal - amount of stops from a specific exposure setting with another. This will help guide you as a photographer to achieve the same or almost the same exposure in the photo, but with different effects depending on the compensated exposure setting. When balancing the value with ISO, you will either have an increase or decrease of noise in your image. This applies to the other exposure settings where you can achieve more or less motion blur with shutter speed and wider or narrower depth of field with aperture.
If you have your camera nearby, grab it and practise with our situational examples below!
Reciprocity Law in Situational Uses
Situation 1: You want to capture more globe details and to have the globe stand out from the background plants. You have used the largest aperture to achieve a shallow depth of field.
Solution: If you’re not satisfied with the result even after using the largest aperture to achieve the shallowest depth of field, you can utilise a longer focal length (35mm to 70mm) to compress the background and magnify the blur outside of the globe (focal point). This will, however, increase your f-stops and thus darken the image. To capture more globe details, we opted to use a faster shutter speed (1/8s to 1/60s), which also darkened the image.
This means that you will now have compensated the underexposed image from the changes in aperture and shutter speed with your ISO (ISO 200 to ISO 2500).
Situation 2: You wish to increase the clarity of the plants to complement the globe in the shot while keeping the same brightness. Additionally, you want to capture more sphere movement.
Solution: To achieve more clarity of the plants, you can use a smaller aperture of f/11. However, using a smaller aperture will darken your image. This means that you will need to compensate for it by using a slower shutter speed or a higher ISO. As we want to capture more motion of the spinning sphere, we used a slower shutter speed of 1/40s that doubled as a solution to brighten the image. We have also increased the ISO to achieve the same brightness as the first shot.
Situation 3: You’re shooting in a dark room and you want to capture more motion details of the spinning sphere. Additionally, you want the plants to be in focus as well.
Solution A: You can use a smaller aperture of f/8 or f/11 to decrease the blur of your plants. You can also use a faster shutter speed to capture more details of the spinning globe. However, this will darken your image even more and you’re left with increasing your ISO to brighten the image. The multiple ISO increase may introduce too much grain in the photo and may not achieve the ideal shot that you want, hence, we have provided Solution B for you below!
Solution B: In this case, you should work to compensate with external factors like introducing a light source (so you don’t have to only use a high ISO value to brighten the image) or to switch up your scene. To decrease the blur of your plants, you can move them closer to the globe, while manually spinning the globe slower to capture the details without using a faster shutter speed.
The reciprocity law in Manual mode is a guide that comes in handy for those wanting to sharpen their problem-solving skills around photography limitations and the exposure triangle.
