What is a “stop” exposure in a photograph?
“Stop” is the step of increasing or decreasing the amount of light entering the lens. A step means that the light on the film or camera matrix will get twice as much (or less).
In photography, “stop” or “step” is a fairly common concept, but many people misunderstand it, many are afraid because it sounds complicated. In fact, “stop” is very simple.
Changing the exposure to a stop (or one step) means doubling (decreasing or halving) the amount of light that enters the lens.
For example, if you hear that you needed to increase exposure by 1 step, it means that you had to capture twice as much light as you received in the photo.
The exposure is a combination of two indicators: shutter speed and aperture value. Each of them can be changed in 1 stop. In addition, the exposure affects ISO.
Since all indicators have different units of measurement, a convenient method for comparison was invented – changing the exposure to stop.
Stop and shutter speed
Camera shutter speed – the time that the camera shutter remains open during photography. The longer the shutter is open, the more light falls on the sensitive element of the camera and the greater the overall effect. Doubling or halving the shutter speed by half produces an increase or decrease in exposure by 1 stop.
A change from 1/200 of a second to 1/100 (increase in time) allows the photocell to get twice as much light, so we can say that the exposure in the photo changes by 1 step, the picture becomes brighter. Similarly, a change from 1/60 to 1/30 allows you to get twice as much light on the photocell, which gives a 1 stop change in exposure.
Most cameras allow you to set the shutter speed in increments of 1/3, so that 3 positions of the shutter speed will correspond to exposure compensation of 1 step.
When adjusting the shutter speed, for example, between 1/60 and 1/125, you can detect 1/80 and 1/100 seconds. This increases the accuracy of exposure, but you must understand that this is between 1/60 and 1/80 one click, but 1/3 stop.
Stop and aperture
The diaphragm is measured using the “f-number”, which is sometimes called the “f-stop”, it shows the size of the diameter of the hole. It must be remembered that a smaller f-number corresponds to a larger open aperture, in which more light falls on the photosensitive element, while a higher f-number means a narrower aperture (less light).
The aperture (also known as the relative aperture) is more complicated to compute, and the step indicating an increase of 1 stop occurs when the aperture is increased by 1.4.
The basic aperture is 1 (although there are not many lenses in the world where the aperture can open up to 1, but they are, there are even those with f less than unity). Multiplying by 1.4, we get the standard aperture row: 1; 1.4; 2; 2.8; 4 etc. each subsequent number indicates that the amount of light passing through the lens has become more or less twice. That is, a picture at 2.8 with a shutter speed of 1/60 second will be highlighted as a picture at 4 with a shutter speed of 1/30. The larger the number of aperture, the stronger it closes and the less light falls on the picture.
Most modern cameras allow you to control the aperture in increments of 1/3 stop.
ISO, or photosensitivity, is responsible for the overall effect of light on the photosensitive element. The lower the ISO, the wider the aperture and the slower the shutter speed.
Doubling the ISO number makes it necessary to reduce exposure by 1 stop. In old cameras, this meant that the photographer installed film with a higher sensitivity in the camera, and in modern cameras, we increased the sensitivity of the matrix to light.
For example, the transition from ISO 100 to ISO 200 doubles the sensitivity of the sensor, so under the same shooting conditions, you should reduce the shutter speed or clamp the aperture by 1 stop. The transition from ISO 800 to ISO 400 – reduces by 1 stop. Most modern cameras allow you to change the ISO in increments of 1 point.
Everything can be changed!
So why are they needed – these feet? Changing a step in the exposure of the frame allows us to directly compare shutter speed, aperture, and ISO. This means that the photographer can easily juggle with these components in order to achieve the desired result.
The fact is that all photographers, except perhaps those who shoot in photo studios, are forced to work with the light that is. We cannot adjust the power of the sun as we need. Let’s look at a few examples:
1) a sports journalist filming fast-moving objects (chess players do not count), is forced to care primarily about exposure. Accordingly, it will not suit the expopair f = 8.0 and 1/125 with the sensitivity of the ISO 100 matrix, which the exposure meter offers him. He needs a shutter speed of 1/500, that is, it is necessary to make the shutter speed shorter by 2 stops.