DETAILED GUIDE: HOW TO MAKE A CORRECT MEASUREMENT AND EXPOSURE IN YOUR PHOTOGRAPHS

The domain of light is what will define you as a photographer and the way to measure it is what will make you a teacher.
If the light in the scene is not correctly measured, the exposure will not be correct and therefore, the quality of the photograph will be affected making all the techniques and tricks you have applied in vain.

Before learning how to correctly measure light, you will see why it is so important to do it: make a correct exposure.

In today’s article I will try to shed light on some subjects that usually scare most photographers who are starting in the wonderful world of photography, but who cannot help knowing if they want to achieve excellent photographs.

Get comfortable, bring your camera close and read on.

DYNAMIC RANGE

Before you begin to see how the light of a scene is measured to achieve a correct exposure, it is necessary that you understand what the dynamic range is and why it is so important when it comes to achieving a correct exposure:

The dynamic range measures the amount of light and dark tones that your camera is capable of capturing in the same photograph, that is, it is the ability of the camera to obtain details in both areas of a photograph, the lights and shadows. The dynamic range sets the amount of tonal nuances that your camera is capable of capturing.

Pay attention to the following photograph: two opposite situations coexist in it, a very light area and the other very dark. These types of situations are impossible to solve by digital cameras so they will not be able to offer you detail in both areas at the same time because their dynamic range is not wide enough. You will have no choice but to lean to get detail in one area or the other: details in the shadows and burnt lights or detail in the very dark lights and shadows.

Dynamic range in photography

The higher the dynamic range of your camera, the more details it will be able to capture and therefore better the quality of the final photographs, yes, as long as you make a correct measurement and exposure of the scene to take advantage of its full potential. Do not worry! Keep reading and you will learn how to do it!

EXPOSITION

Exposing is the action by which you allow a particular scene to be printed, that is, captured by a sensitive material. In analog photography, the sensitive material is the film and in digital photography, the sensor.

Contrary to what it may seem to you, exposure is not the time that photography is exposed to light: time is only one of the three variables controlling the entry of light into the focal plane (sensor) to achieve correct exposure:

1. ISO sensitivity: indicates the amount of light needed to be able to take a picture: the greater the light in the scene, the lower the necessary ISO value and vice versa. In analog photography to change the ISO sensitivity you had to change the film, but in the digital age, it is possible to adjust it from the menu.

As I mentioned in the article “24 ways to get super sharp photos” , if you raise the ISO sensitivity too much, your photographs will have higher noise, less sharpness and therefore lower quality. Use high ISO values ​​only when you have no other alternative, that is, when you cannot achieve a correct exposure by compensating for the “lack of light” product of using a low ISO using the other two variables: reducing the shutter speed or opening the diaphragm .

2. Diaphragm aperture: The diaphragm is a device that is within the lens of your camera and allows you to control the amount of light that reaches the focal plane (sensor), along with the shutter speed, and at the same time, regulate the depth of field of the photograph, that is, what will come out of focus and not.

The more you close the diaphragm (f / 16), the greater depth of field you will get in your photographs (greater sharpness) but less light reached the sensor, compensating for the lack of it or increasing the ISO sensitivity or decreasing the shutter speed. The more you open it (f / 1.8), the lower the depth of field will be (greater blur or bokeh) and more light will reach the sensor, being able to use lower ISO values ​​and faster shutter speeds.

3. Shutter speed: is the time that the shutter remains open allowing light to reach the sensor. The higher the shutter speed (1/1000), the lower the light that reaches the sensor, and the lower the speed (1 ”), the greater the light that passes through the shutter.

By adjusting the shutter speed you will not only achieve lighter or darker photographs, but you can also convey the sensation of movement using very slow speeds or very fast speeds, you will be able to completely freeze a scene .

Landscape during sunset

How do you balance the 3 exposure variables?

An excellent tool that will help you achieve correctly exposed photographs is the so-called “reciprocity” that is neither more nor less than a rule with which you will obtain the same exposure (photograph) with different combinations of speed, aperture and ISO sensitivity. No, don’t panic yet! Here I explain:

Law of Reciprocity : the 3 variables to achieve a correct exposure do not have a unique combination, but you can adjust each of these differently and achieve exactly the same exposure.

Look at the following image: in it you can see different combinations of aperture of the aperture and shutter speed that will result in the same exposure, that is, the same photograph, neither more nor less exposed, the same.

How to Balance Exposure Variables

A very simple way to obtain the same exposure with different combinations of ISO, speed and diaphragm is by doing “doubles and halves”. What does this mean? It is very simple pay attention:

If you leave the aperture of the fixed diaphragm, you can obtain the same exposure by modifying both the ISO sensitivity and the shutter speed as follows:

 

The exposure in all cases will be the same: if you double the ISO sensitivity, to achieve the same exposure you can increase the speed to double and still retain the same exposure in your photo.

The same happens if you set the ISO sensitivity and modify the speed and aperture of the diaphragm:

In all combinations you will get, again, the same exposure. Note that this time the relationship between the two is inverse: when closing the diaphragm you must decrease the speed in order to compensate for the light input to the sensor.

The last relation that remains to be seen is setting the shutter speed, obtaining the same exposure by modifying the ISO sensitivity and aperture of the diaphragm, to obtain the same final photograph.

The law of reciprocity is extremely useful: with it you can adjust the parameters of the shot to be made in a more conscious and controlled way, taking full advantage of the power of your camera.

The key so that you can understand perfectly how it works is by taking your camera and doing the tests yourself with any object you have on hand. Take any of the examples that I mentioned before and start taking photos.

When is a photograph correctly exposed ?

A photograph is correctly exposed when the sensor is able to capture as much information (light) and tones (dynamic range) as its capacity allows. Imagine you have a camera capable of taking photos at a resolution of 18 mega pixels, but you shoot only in 8: you would be wasting the potential of your camera to work with better resolutions.

The same goes for light: if your camera is capable of capturing much more light than you, by adjusting the 3 exposure variables you allow, you will be wasting a lot of information that the sensor is capable of capturing, but that you are leaving out .

3 Exhibitions

The photograph of the medium is correctly exposed, it may not be the final result you want for it, but it was possible to take advantage of almost the entire capacity of the sensor to register light, that is, its dynamic range was maximized. Once you have achieved a correct exposure, you can edit it * on your computer without losing quality.

If you over or under expose your photographs, you will be sacrificing a lot of valuable information, which you will not be able to retrieve later by editing, so if once on the computer you want to “lighten” or “darken” the photographs, you will subtract them a lot of quality since the Computer will have to “invent” information where there is none.

* edit is only adjust certain parameters such as exposure, luminance and shadows on the computer unlike the touch-up where the scene is modified directly by altering it.

Photograph of a photograph

Achieving correct exposure will be easier if you take advantage of the following tools that you have at your fingertips (on your camera):

• Exposimeter: is responsible for measuring the “amount of light” necessary for a photograph to be exposed correctly. Once it receives the light reflected by all the elements of the scene, it calculates an average value of all the tones, light and dark, and adjusts the values ​​of speed, aperture and ISO sensitivity to be able to obtain a correctly exposed photograph (this is not so so but you’ll understand later).

In automatic or semi-automatic modes it is essential since it is the camera who decides which are the correct exposure parameters for each shot, instead if you shoot in manual mode, you can use it to measure the light of the scene and adjust these parameters yourself .

Its use is very simple: by the sign “+” or “-” it will indicate if the scene is over or under exposed respectively.

• Histogram: it is a graph that shows how all the tones of a photograph are distributed, whether gray or not (RGB colors: blue, red and green) according to the dynamic range that your camera can capture.

In this you can see how many light, medium and dark pixels are in your photographs, that is, how it is exposed. A photograph is correctly exposed when you take full advantage of the ability of your sensor to capture tones and this is when, not only are there not parts outside the range that your camera is capable of capturing, but also when the histogram is most “right. ”Possible, that is, as close to the right edge as possible.

In the digital age of photography, the more light tones you capture (the more right-oriented histogram possible), the lower quality loss your photographs will suffer, even after editing.

Histogram

Check your camera’s manual to learn how to visualize the histogram once your photographs are taken, or, if your camera allows it, view it live through the screen or “live view” at the time of taking your shots.

Step by step for proper exposure:

For a correct exposure

While each photographer has his method to achieve a correct exposure, it is likely that at first you feel a little lost and do not know where to start. It’s normal for you to feel a little overwhelmed, nobody was born knowing. Here is a step by step so you can use it as a guide until you become a teacher in it:

  1. Select the mode of your camera in Manual.
  2. In the menu of your camera select the area of ​​measurement of the light in time.
  3. Adjust the ISO value according to how your camera processes the noise and your tolerance for it.
  4. Adjust the aperture or shutter speed according to the type of picture you want to achieve: dynamic or static. If you are going to photograph a landscape, adjust the diaphragm so as to obtain greater depth of field and that the photo comes out as clear and in focus as possible.
  5. To adjust the exposure value you are missing, you must make a measurement of the lightest tone in the scene.
  6. Once your picture is taken, take a look at how it looks on your camera screen but in the “histogram” mode. In this you can see how they have all been light and dark distributed in your photography.

Why not use the modes predefined by your camera?

All cameras come equipped with what is known as “photometer”, which is responsible for “measuring the amount of light” in the scenes you are going to photograph. This photometer captures the light that is reflected by the objects towards the camera and measures its intensity so as to automatically adjust the exposure for the shot, if you use the predefined modes.

The problem begins here: said photometer is calibrated to capture the light of a scene as if all the objects in it were “MEDIUM GRAY”, which is something like an average between light and dark tones that can occur in a scene.

Beyond the exposure of your camera, it indicates that the exposure is correct, in very light or very dark situations, it may indicate that the photograph is on or under exposed when in fact it is not.

Another problem even greater than the previous one is that, the photometer of your camera when taking all the colors as neutral gray, tends to center the position of the histogram, thus wasting a lot of information and not using the maximum potential of your camera.

Try to photograph a white sheet in an automatic or semi-automatic mode and you will see that it is rather gray instead of white. This can only be corrected, either with postproduction but you will lower the quality of the image, or by making a correct exposure in manual mode.

The Middle Gray

The dotted lines of the previous image mark in the histogram the capacity of the sensor (dynamic range) that has been wasted for not making an exposure that can take advantage of all the capacity of this to capture tones in a scene.

Anyway, if you have a digital compact camera where you can see on the screen how exactly the photograph will look before taking the shot, the difference between the measurements of the automatic modes and the one that you can get to do in the manual mode will be very similar. Only in certain cases will you be able to improve the measurement that the camera makes yourself, in fact, in many cameras of this type, it is not possible to adjust the exposure parameters manually.

FIRST MEASURE, THEN EXPOSE

The key to achieving a correct exposure is to make a good measurement of the amount of light in the scene and once this is done, expose for the lighter tones. What does this mean? Keep reading and you’ll understand.

MEASUREMENT

The measurement is, as the name implies, the process that you must carry out to measure the “amount of light” that a given scene has in order to be able to achieve a correct exposure, that is to say that it is not over exposed (burned) or underexposed (dark).

This means that, whenever you are ready to take a picture, you must measure the amount of light that is reflected by the objects to be able to adjust the parameters for a correct exposure: aperture of the diaphragm, shutter speed and ISO sensitivity and thus achieve , make the most of the dynamic range of your camera and therefore maximize its potential to capture information.

Failure to adjust the parameters correctly will mean having to force subsequent processing with a consequent loss of quality or even an irreparable loss of data:

  • If your photo has been underexposed, when you try to “clarify” it on the computer, you will generate noise, lowering the image quality. In the histogram you will see that there is a large proportion of information that has been left out of what your camera is capable of capturing (its dynamic range). There is a large portion of data that is left out of the exhibition, losing details in dark tones.
  • If your photo has been overexposed, that is to say that you have lost detail in the lighter tones, and then you try to correct it in the post processed, the computer must invent information where there is none since the pixels, were completely white, losing again quality. The histogram will be more oriented to the right and a large proportion of data that your camera could have taken advantage of, have been left out of the exposure. This is known as a “burned area”, that is to say without detail on the targets.

How does the light measure me?

  • With the camera’s exposure meter: it is the most common method and used by most photographers whether they are aware of it or not. Even if you don’t notice it, your camera’s photometer is constantly calculating the amount of light in the scene that is reflected towards the sensor so that you can provide information so you can adjust the exposure of the shot or automatically adjust it if you shoot in modes automatic or semi automatic. Remember that your camera’s exposure meter is calibrated to a “neutral gray” so it will not give you the best possible exposure to achieve in one shot.
  • With a handheld photometer (incident or reflected): handheld photometers are used by professional photographers, mostly, to measure both the light that affects a certain object as well as what it reflects towards the camera. Working with them means more time available to plan the scene, measure the lights of the entire scene and average the lightest and darkest measurements so as to obtain a correct exposure in both tones.
Photometer

Light measurement modes

As you may have noticed, the best way to take advantage of all the potential you have in your hands (your camera) and in your eyes (yourself) you must measure the light in your photographs yourself.

No matter how modern your camera is, they all have the same inconvenience when using automatic modes: they cannot guess which is the most suitable mode for the picture you want to take, you must do it yourself.

Your camera has different modes to be able to measure the light in a scene, but as Mario previously published the article “Examples of light measurement modes in photography” where he explains how and when to use each of these modes, I recommend Take a look before going out to practice.

As a summary here I briefly explain each of them:

  • Matrix or evaluative measurement: measures the light of the whole scene as a whole and tries to achieve an exposure for all the tones present in it.
  • Partial evaluative measurement: it works in the same way as the matrix, but in this case the light measurement is only carried out in the central area of ​​the photograph.
  • Punctual measurement: this is the way that I recommend you to use since with it, since it only uses a point that is usually the center (in some cameras you can modify it to your liking) to measure the light, you can make the measurements yourself according to to the tones you want or not highlight in your photographs.

How to carry it out?

As I told you before, there are many situations in which your camera’s photometer will indicate that the photograph is correctly exposed when in fact it is not (remember the example in the previous blank sheet).

The key to making a good measurement is “expose for the lightest tones” that is, measure the amount of light from the lightest area in the scene to be photographed and adjust the exposure values ​​so that that area comes out as clear as possible ( more to the right of the histogram): if the lightest tone of the scene does not overexpose, that is, it is not burned, you will ensure that all the darkest tones that are left in detail, taking full advantage of the dynamic range.

You may be wondering: How do I do it if I can’t trust the camera’s exposure meter? It is true that you can not always rely on the exposure indicator of your camera since as we saw earlier, it does not take full advantage of the capacity of your sensor and may indicate that there is over or under exposure when there really is not.

What you should know is the limit of over exposure of your camera : perform several tests photographing very clear objects in order to know how far your camera is able to capture detail in the lightest tones. It doesn’t matter if your camera tells you that the photo will be exposed because when you look at the histogram you will notice that there is no area outside the graphic. Once you know how far you are able to overexpose without losing detail, you will be ready to take measurements in your photographs.

You can use both the histogram, as well as the “highlighted areas” mode when reviewing the photo. This mode will show you your photo on the screen of your camera and will indicate which areas have been “burned” by a blink. Try to minimize these areas.

Now yes: Step by step

  1. Set your camera in manual shooting mode.
  2. Set the light measurement mode in the “spot” mode.
  3. Find the lightest tone in the entire scene that you are preparing to photograph.
  4. Measure your picture at that point.
  5. Configure the exposure parameters according to the aesthetics you want to give your photography, always trying to keep the ISO sensitivity at the lowest possible value so as not to lose quality product of the noise.
  6. Shoot and capture the photo.

The measurement was carried out in a strut mode on the white stripes of the small child’s shirt (1).

In this way you will have managed to maintain the maximum level of information in each of your photographs. If you are still not satisfied with the result, you can, in the process, darken it until you obtain the desired photograph but minimizing the loss of quality.

In case you have not been clear when reading it, you can watch the following video, one of the many that you can find on the internet, where they explain how to make a correct measurement in a simple and synthetic way:

Today’s article may seem more complicated than it really is. The key to being able to understand it well is to have your camera at hand and carry out the tests yourself. Patience will be your best ally and if you have any questions, do not hesitate to share it in the comments.

I hope you liked today’s article! Please practice the above, take pictures, lots of photos, trial-error, and as always remember to recommend the article on your favorite social networks.


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