Reciprocity Laws


The laws of reciprocity as it relates to photography illustrate the inverse relationship between the shutter sped and the aperture of the camera to achieve a proper exposure. Understand the reciprocity laws with information from a professional art and commercial photographer in this free video on photography.

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Video Transcript

Hi, I'm Rebecca Guenther with and I'm going to talk to you about the laws of reciprocity. So what the equation, the mathematical equation on this states that exposure equals time times intensity. Broken down what it means is to achieve the exact same exposure in two photographs you have to look at the intensity of the light and also look at the amount of time that the shutter is open. For example, if your shutter speed is going to be maybe at a two-hundredth of a second, your aperture is going to be open more to maybe five point six, allowing a lot more light to come into the camera but your shutter speed can be faster because more light is pouring in at once. However, if your aperture is set to F22 which is a very, very small hole and only a very little bit of light is getting in, you're going to need to have a shutter speed of more like a fifteenth of a second or even a full second or something like that, because a lot less light is going to be coming in, you're going to need to have the shutter open for a lot longer exposing the film plane or the sensor if you're shooting digitally to the light that is coming in. So it basically just states that however you achieve your exposure there is going to be an inverse relationship between the shutter speed and the aperture of the camera. And that's just really basically the law of reciprocity.


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