Photography etymologically means to paint / write with light, our pencil/brush is light, but what is our canvas?, some photosensitive material, a film, photodiodes of a sensor, etc., some kind of surface that reacts to light.

With the above we can understand the importance of exposure, exposure is the amount of light that reaches the photosensitive material to form an image.

Underexposure and overexposure

If you have decided to immerse yourself in the world of photography these are two words that you hear a lot from now on. When the amount of light that is allowed to pass is too small for the image to be captured, it is said that the image is underexposed, but if, on the contrary, you let more light pass than necessary, the photosensitive material becomes saturated, in which case the image capture uncorrectly, then talk about overexposed image.

Underexposed image, correctly exposed and overexposed

As we see in the image and we have inferred, if there are incorrect/inefficient ways to explain it is logical to assume that there is also a correct way to do it, but how is it achieved?

Time, Aperture and ISO

These are the tools that we have in any camera at present to control the amount of light that reaches our sensor (digital cameras), they are not independent but affect each other.

The above image explains how the relationship between these three variables, to explain it quickly, each side corresponds to one of these mechanisms and that as one of the values ​​grows (moves towards the hands of the clock) the other two must move away from him, that is, move towards the handsome corner on that side, in order to preserve the same exposure.

Time or speed

As you may have imagined, one of the ways to control the passage of light is to restrict the time the sensor remains exposed to it at will. The shutter is the mechanism that takes care of this, it is like a gate that opens for a period of time and then closes and does not let light in. The time it takes to do the opening and closing travel is known as shutter speed. It is expressed in fractions of up to 1/8000 of a second (depending on your camera) up to 30 seconds or even indefinite, being the user of the camera the one that determines with a second press when the shutter time finishes, I repeat, this depending on the model of your camera.

As for the obturation, there is both mechanical and electronic, but that will be discussed in another article.

Freeze movements or paint with light

The very high shutter speeds are useful for freezing movements (as in the first image), on the contrary slow fillings are useful when we want to capture that movement as when we paint with light (second image).

Photos moved or trepidated

An advice so that your images don’t move is to increase the shutter speed, how much?, a reference is the rule of the inverse of the focal, that is, if your lens is a 50mm don’t shoot less than 1/50 , or if you use a 200mm don’t shoot less than 1/200.

AperturE

The aperture refers to the hole through which light enters. In digital cameras this hole is variable and controlled by means of a gate called a diaphragm that is made up of several blades that when rotated change the size of the aperture.

The aperture as a fraction between the focal distance that is denoted by f and the aperture diameter that is the number that accompanies the f, for example. f/2 or f/16, can also be expressed in the form (most common) 1:2 or f:16, respectively.

Something important to mention is that the numbering of the aperture is counter-intuitive, that is, a smaller number of f greater will be the aperture and more light will let pass, and the opposite, to a greater number of f smaller will be the aperture.

The lens manufacturers usually place the minimum aperture next to the focal length, for example: 35mm 1:1.8, where 1.8 is the minimum aperture of the lens. If it is a zoom lens as the kit lenses appear two minimum aperture: 18-55mm 1:4-5.6, it means that at 18mm its minimum aperture is 4 but at 55mm it is 5.6. There are also zoom with constant minimum aperture, for example: 17-55mm 2.8, we understand that 2.8 will be its minimum aperture for both 17mm and 55mm.

Depth of field

Depth of field

As you can see in the image there is part that appears blurred, without focus and another in the middle that appears focused, then, this last is what is known as depth of field, an area seen from the objective where everything that enters it appears in focus, and consequently everything that is out of this, both behind and ahead, will appear out of focus.

One of the factors that influences the depth of field is the aperture, the greater apertures produce lower the depth of field, that is, the less things will be in focus, and the lower apertures greater depth of field will be.

In portraits it’s quite common to have reduced depths of field looking for the bokeh effect
For landscapes large depths of field are common

ISO sensitivity

Of the three this is the most complicated concept to explain in a simple way, so here we go.

ISO refers to the sensitivity of our photosensitive material, and with sensitivity refers to the amount of light that is required for it to react, that is, paint something.

ISO is a standard of sensitivity which is independent of the manufacturer, ie 100 ISO will be the same whether the camera has been manufactured by Fujifilm, Sony, Pentax, Olympus, etc.

The ISO value is proportional to the sensitivity, that is, at the higher ISO value less light will be necessary to form an image.

In film reels/rolls the sensitivity is fixed and is specified in the film box.

In digital cameras the value of ISO can be adjusted in the configurations, being able to raise it if the scene requires it, if we have very little light.

You have to be careful when uploading the ISO because with it appears noise or grain in our picture, the higher the ISO, the more noise there will be in our photography.

My final recommendation is to leave the ISO as a last option, play first with the two values ​​I mentioned at the beginning and if there is no alternative to increase the ISO.


Fuentes:
https://en.wikipedia.org/wiki/Exposure_(photography)
https://en.wikipedia.org/wiki/Shutter_speed
https://en.wikipedia.org/wiki/Aperture
https://en.wikipedia.org/wiki/F-number
https://en.wikipedia.org/wiki/Film_speed#Digital