To get photos with a good amount of light you need to make a proper photographic exposure: here's what it consists of, the various types and how they work.
When you take a photograph, which from the Greek means writing about light (where photo is light), light is the first component that you must learn to manage. The one that underlies the very existence of the photographic image. When we take a photo, all we do is open what is called in technical terms the shutter, located behind the lens, allowing the light to hit a sensor inside our camera, which replaces the old film that was extremely sensitive to light, fixing itself in a static image of what was in front of our lens at that precise moment.
Photographic exposure is therefore the parameter that allows us to control the amount of light that the shutter actually lets in. This is the basis of that extremely modern art, born a little less than a century and a half ago, which is called photography. Now let's find out how to get photographs with proper exposure, so that they don't turn out too dark (underexposed) or too bright (overexposed).
How to Control Photographic Exposure
The easiest way to control the exposure that the photo you're going to take will have is simply to look into the viewfinder of your camera. On one side of the screen is a graduated scale called an exposure meter with a pointer. If the pointer indicates zero, the exposure is correct, while if it is on the left side the photo will be dark or, vice versa (pointer moved to the right side) overexposed. In addition to the exposure meter, the components or parameters that allow you to dynamically manage the exposure of your camera are the aperture, the sensor and the shutter.
Modern digital cameras allow you to set these three parameters manually or automatically, using preset settings decided according to the conditions (day/night) or the type of photo to be taken (portrait/panorama). By changing these three parameters, the exposure will vary, and consequently the position of the pointer on the exposure meter. At the moment of shooting, the sensor absorbs the image passing through the lens by means of light. Between the lens and the sensor we then find in sequence diaphragm and shutter. The first one is a sort of aperture on which we can act: the wider we keep it, the more light will enter at the moment of shooting.
The diaphragm, whose value is expressed by a unit of measurement called focal ratio (F/) also determines the depth of field of the photo (long or narrow), the portion of the image that will therefore be in focus. The shutter, on the other hand, is a kind of curtain or shutter that opens only at the moment of the shot, as we have seen. It determines the time, expressed in fractions of a second. Also in this case, varying the time in which the shutter must remain open, we are going to vary the amount of light that will then hit the sensor inside.
The combination of these 3 elements gives birth to the art expressed in every single shot by the professional photographer, determining not only the exposure, but also the final result, technical but above all aesthetic, that will characterize the photo. Once you have assimilated the basic concepts and parameters, perhaps with a short course in basic photography, the best advice is to start taking pictures by experimenting, trying and trying again the adjustments. Let's see now specifically how each of these elements works.
Photographic exposure: the sensor and the ISO sensitivity
The ISO, generally measured with values starting from a minimum of 100 and then moving to powers of two (200, 400, 800 and 1600), regulates how receptive the sensor must be to light. The higher the value, the more light the sensor will be able to capture. If it is dark, you will have to increase the ISO. If it is a nice sunny day, vice versa, lower it. If you increase the ISO, the image loses its sharpness and becomes grainy.
In this case you have to evaluate the quality of the sensor, therefore the quality of the camera itself. To be of good quality, therefore, the camera must be able to take sharp photos even at high ISO. At the time of film, the sensitivity was given by the type of film one intended to buy. With the advent of digital cameras you simply have to adjust the ISO of the sensor located inside by pushing a simple button.
Photographic exposure: diaphragm or aperture
The aperture of the diaphragm determines the width of the hole behind which the sensor is placed. The aperture, which as we have seen also influences the depth of field to be given to the image, thinks strangely backwards. The higher the value set in front of the F of the unit of measurement, the smaller will be the actual opening of the hole and therefore the minimum amount of light that will reach the sensor at the time of shooting. F/4 is the maximum aperture (only the foreground will be in focus), F/22 the minimum aperture (the whole image will be in focus).
Photographic exposure: shutter or shutter speed
The parameter determined by the shutter, so to speak, is the so-called shutter speed, or exposure time, which is the time interval during which the shutter remains open and the sensor is therefore left exposed to light. The less light there is in the environment, the longer the time interval must be to allow the light to hit the sensor. A shorter exposure time will tend to crystallize the moving object, which will be still and sharp in the picture, vice versa if you increase the exposure time, the sensor will catch it with a strip of movement, with a loss of sharpness that will have to be adjusted, up to an authentic motion blur that will emphasize the movement even creating particular, artistic and original effects.