Let's Get Technical
In photography, the f-stop, also known as the f-number, is a measure of the size of the aperture in a camera lens. The f-stop is the ratio of the focal length of the lens to the diameter of the aperture.
The f-stop scale is logarithmic, which means that each increment on the scale represents a doubling or halving of the size of the aperture. For example, an f-stop of f/2 is twice as wide as an f-stop of f/2.8 and four times as wide as an f-stop of f/4.
To calculate the f-stop, divide the focal length of the lens by the diameter of the aperture in millimeters. For example, if a 50mm lens has an aperture of 25mm, the f-stop would be calculated as:
50mm / 25mm = f/2
So the f-stop for this example would be f/2.
It's important to note that the f-stop not only affects the amount of light that enters the camera, but also has a direct impact on the depth of field in an image. A larger f-stop (smaller aperture) results in a greater depth of field, while a smaller f-stop (larger aperture) results in a shallower depth of field.
STOPS of LIGHT
In photography, the term "stops of light" refers to the amount of light that is allowed to enter the camera through the lens. The term is used to describe the exposure settings used in photography to control the brightness of an image.
A stop of light is a doubling or halving of the amount of light entering the camera, and each stop of light represents a change in the exposure value (EV) by one unit. For example, if you increase the exposure by one stop, you are allowing twice as much light into the camera as before, and if you decrease the exposure by one stop, you are allowing half as much light into the camera.
Exposure settings that affect the amount of light entering the camera include the aperture, shutter speed, and ISO. By adjusting one or more of these settings, you can control the exposure and adjust the brightness of your images.
For example, if you want to increase the exposure by one stop, you can do so by either widening the aperture by one stop, slowing down the shutter speed by one stop, or increasing the ISO by one stop. Each of these adjustments will have an impact on the final image, so it's important to understand how they work and how they can be used to control the exposure.
THE INVERSE SQUARE LAW
The inverse square law is a mathematical principle that applies to many physical phenomena, including the propagation of light and sound. The law states that the intensity of a point source of light or sound decreases as the square of the distance from the source increases.
In the case of light, the inverse square law states that the amount of light that falls on a surface decreases as the distance from the light source increases. This means that if you double the distance from a light source, the amount of light that falls on a surface is reduced to one-fourth of its original intensity. If you triple the distance, the intensity is reduced to one-ninth, and so on.
The inverse square law is important in photography because it helps to explain why the light from a small light source like a flash or a candle will fall off quickly as you move away from the source, while the light from a larger light source like the sun will fall off more slowly.
The inverse square law also affects the exposure settings used in photography. If you take a photo with a flash or other small light source and then move away from the source, you will need to adjust the exposure settings to compensate for the decrease in light intensity, otherwise your image will be underexposed. On the other hand, if you move closer to the source, you will need to reduce the exposure to avoid overexposure.
In short, the inverse square law helps to explain why light decreases in intensity as you move away from the source, and it has important implications for exposure and lighting in photography.
The inverse square law applies to flash photography in the same way it does to other forms of light. It states that the intensity of light from a point source decreases as the square of the distance from the source increases.
In flash photography, this means that the amount of light that reaches a subject decreases as the subject moves away from the flash. This decrease in light intensity can lead to underexposure if the flash is not adjusted accordingly.
For example, if you take a photo with a flash and the subject is 2 meters away from the flash, the amount of light reaching the subject is proportional to 1/(2^2) = 1/4. If the subject moves to 4 meters away, the amount of light reaching the subject is proportional to 1/(4^2) = 1/16.
To compensate for the decrease in light intensity, flash photographers will often use techniques like increasing the power of the flash, moving the flash closer to the subject, or adding additional flashes to the setup.
In short, the inverse square law for flash photography states that the amount of light from a flash decreases as the distance from the flash increases, and it is important for flash photographers to understand this principle in order to achieve properly exposed images.