Understanding exposure is essential to becoming a creative photographer and moving out of “All Auto” mode.
Ever since Kodak coined the slogan “press the button and we’ll do the rest”, manufacturers have always dreamed of making a camera that can expose photos automatically.
Except it doesn’t work that well.
In order to take pictures, one day or another, you have to get out of the “All Auto” mode and expose your pictures yourself.
This requires an understanding of the exposure mechanism.
And we’ll see together that it’s not that complicated.
Understanding the exposure
What do you call the exposure
Remember this simple rule: a well exposed image is neither too dark nor too bright.
It has received just the right amount of light.
On the left, the photo is well exposed – In the middle, it is too light or overexposed – On the right, it is too dark or underexposed An image that is too bright is said to have been overexposed and an image that is too dark is said to have been underexposed.
How does the camera expose a photo?
Photography is the art of writing with light.
And to write an image correctly, you have to start by sending the right amount of light to the film or sensor.
The camera measures the ambient light
To determine how much light should reach the sensor, the camera uses a light meter that measures the intensity of the available light through a photocell.
From this measurement, it will calculate the amount of light that must reach the sensor and choose its settings accordingly.
When you will leave the mode ” TOUTOTO ” it will be you, who from the same measurement will choose the settings, but let’s not anticipate.
The camera doses the amount of light that will reach the sensor…
In order to dose this quantity of light that will reach the sensor, your camera has 2 complementary mechanical parts: the diaphragm inside the lens and the shutter.
Let’s see what it is all about.
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It is a set of metal slats at the back of your lens that closes or opens and allows you to dose the amount of light that will pass through the lens and reach the sensor.
It behaves like the pupil of your eye, which enlarges or shrinks depending on the brightness.
Adjusting the iris is called adjusting the aperture.
The shutter is a metal curtain that opens for a given time and lets the light through to the Shutter-and-Sensor-001-1-2 Sensor.
Only when you press the shutter release button, the shutter opens to let the light through and record the picture.
The shutter does not dose the amount of light that will pass through (the aperture does this), but the amount of time the light is “allowed to pass …
1 second, 2 seconds, or only 1/1000° from Setting the time the shutter opens is called setting the shutter speed.
Every camera has these 2 elements and will use them to dose the exact amount of light reaching the sensor.
View the exposure mechanism
To understand the exposure and the path of light through the lens, imagine a corridor with a window with closed shutters at one end and a closed door at the other end.
The sensor is behind the door.
With the window closed, no light enters the room.
The more you open it, the more light there is in the room.
But the light does not reach the sensor because the door is closed.
Only when the door is opened can the light through the window finally reach the sensor and “create” the picture.
The light enters through the window and advances to the door.
If the door opens, it enters and impresses the sensor, which records the photo.
In our hallway analogy, the diaphragm plays the role of the shutters and the shutter the role of the door that blocks the light.
Light passes through the lens and the diaphragm (shutters), but the shutter (door) protects the sensor (in blue) – as long as it is not opened.
Exposure is made by adjusting the aperture and shutter speed.
The aperture controls the amount of light that passes through the diaphragm and into the sensor and the shutter speed controls the amount of time the light will pass through the diaphragm.
To help you understand the exposure, Xavier Navarro uses the analogy of a glass of water, in his excellent blog: you can adjust the amount of water by opening the tap more or less and deciding how long you leave it open …
you will find the link at the bottom of this article.
Exposure in Auto Mode
When your camera is set to Auto …
mode, it will adjust the shutter speed and aperture for you.
It does this according to a number of parameters that it takes into account but forgets others.
Sometimes the image is well exposed, other times not, but you don’t know why.
Above all it prevents you from making creative photography by deciding for yourself which settings to use as we saw in a previous article.
What is meant by a couple of exposures?
It is often referred to as exposure torque because – as we have just seen – it is achieved through aperture and shutter speed.
But you’ll also hear about an exposure triangle because many photographers include ISO sensitivity in their exposure settings.
If this is correct in practice, I find it confusing to understand, so I’ll talk about it in a separate article.
This time I’m going to ask you to picture a scale with its 2 trays.
Let’s say that one plate represents the aperture and the other represents the shutter speed.
When the 2 plates are in balance, the picture is well exposed.
Although let’s say the camera has selected a shutter speed of 1 second and an aperture of f8.
Imagine that I intentionally set the shutter speed to 2 seconds.
What would happen? The same amount of light will reach the sensor (I didn’t change the aperture), but for 2 seconds, i.e.
twice as long.
The picture will be too clear (it received twice too much light).
The balance between diaphragm and velocity will be upset.
The balance is no longer in balance.
Now suppose I do the opposite: I open the diaphragm more (f5,6), but keep the speed of 1 second.
This time it is the quantity of light reaching the sensor that is thus increased.
The result will be the same, the image will be too clear.
Does this mean that only this 1 second setting for f8 is possible?
Of course not (it would be complicated to make a clear picture at this speed): all equivalent pairs will do.
The principle is simple:
- if you increase the speed > you have to close the diaphragm more…
- if you reduce the speed > you have to open the diaphragm more > if you reduce the speed > you have to open the diaphragm more
- if you open the diaphragm further > you need to reduce the speed
- if you close the diaphragm further > you need to increase the speed
In other words, if you touch one of the pans on the scale (aperture or speed) you must COMPENSATE with the other parameter.
To fully understand the exhibition and the story of this “couple”, here is a small example showing you the equivalent of a cutlery-cup-slide1
As can be seen in the following table, there are approximately 7 equivalents to the Opening/Speed F2 / 1/1000° of a second torque.
Seven settings that will give an absolutely identical result in terms of exposure.
Seven variants that will give a balanced balance in all cases.
Your camera will therefore choose one of these 7 combinations.
According to which criteria? In AUTO mode, it is very difficult to say.
If you switch to SCENE mode, you give the camera an indication of what you want to do and it will then choose a more suitable combination:
>> For example, if you select the sport mode, the device will choose the torque F2 / 1/1000° because it will prefer a fast speed to “freeze” the action.
This is why we talk about exposure torque.
Understanding exposure implies having assimilated that for a given measurement by your camera, you will have several possible choices (exposure torques) which will all give a well exposed image.
You will choose one or the other shutter speed / diaphragm pair according to creative criteria.
Now that you have understood (well I hope) the mechanism of photo exposure you can go and see the article explaining how to easily expose your images, in Aperture Priority, Shutter Priority or Manual exposure modes.
These 3 modes allow you to CHOOSE yourself the most suitable exposure couple for what you want to do according to creative criteria.
What is the exposure ?
Even in more banal lighting conditions, it is important to know a few tricks that will allow you to best render a scene, without seeing too many surprises such as “sky completely burnt out” or “photo all black”!
An underexposed photo
An over-exposed photo
Capturing the light: how does it work, exactly?
First of all, a small point on the operation of the camera (whether digital or silver, by the way):
Light enters the camera through the lens.
The photographer presses the shutter release: we let this light reach the sensor (or the film).
We say that we “expose” the sensor (hence the expression exposure time…).
The photo is recorded on the card.
A simple observation (and very important): the more light is allowed to enter and reach the sensor, the clearer the picture will be.
On the contrary, the less light you let in…
the darker the picture will be.
And this is where it becomes interesting, in practice! Indeed, there are two ways (detailed in the following sections) to play with the amount of light that enters the camera and reaches the sensor: the exposure time and the aperture of the diaphragm.
The principle is therefore very simple: the more time you allow the light to enter, the greater the amount of light, the clearer the photo.
A little precision: this exposure time is measured in thousandths of seconds, hundredths of seconds, tenths of seconds, seconds and sometimes even in minutes or even hours for very very long exposures! We have the following different situations:
Short exposure time
Little chance of making a blurry picture.
Perfect for moving subjects (sport…).
Needs a lot of light, otherwise the picture is dark (“underexposed”).
To be used when there is a lot of light: outdoors in good weather for example, or if you can use the flash to bring light.
Long exposure time
A lot of light has time to reach the sensor, so you can take a picture bright enough even in the dark.
It is also possible to make nice “net” effects.
A blurry picture unless you don’t move or use a tripod.
Use when there is little light and you don’t want to use the flash.
Of course, some modulations can exist with this picture!
The aperture of the diaphragm is simply the size of the hole that lets the light through to the lens.
The bigger it is, the more light enters, the smaller it is…
Shutter speed and exposure time work together: it’s a question of proportionality! The more you open the diaphragm, the less you need to expose for a long time, so you can increase the shutter speed, and vice versa.
Don’t panic: the camera takes care of making this correspondence (except in fully manual mode): you set the shutter speed, it takes care of the aperture, you set the aperture, it takes care of the shutter speed.
Magic, isn’t it?!
Effect of the aperture on the picture
So why, you may ask, bother with these two parameters if the end result is the same? There’s a good reason: the aperture of the diaphragm has an incidence on the rendering of the picture, and this incidence is significant: it’s called depth of field (for more details on this subject, see the page dedicated to depth of field).
To put it simply: the larger the aperture, the smaller the depth of field (in other words, only a small part of the image is sharp, the rest is more or less blurred), and the smaller the aperture, the larger the depth of field (the picture tends to be sharp in all areas: subject, background, etc.).
Conventional Aperture Aperture Values
There are so-called conventional diaphragm opening values.
Fixed by an international convention, they represent as many aperture values as are generally found on cameras.
Of course, this list of conventional apertures is not exhaustive: some lenses open more, and/or close more.
These aperture values are as follows:
Good to know: the values announced above were not chosen by chance.
Indeed, from one value to the next, the amount of light that the lens lets through is multiplied by two.
For example, when you go from an aperture ƒ/2.8 to an aperture ƒ/4, half as much light will reach your sensor! You can use these aperture values as a guide, especially when you switch from one camera to another.
Exposure in photography
As a photographer, the first thing you need to know is the potential of your camera.
Once you know all it can do, you can take full advantage of its features.
Once you have mastered the use of your camera, there will come a crucial point that will set you on the road to success, the control of light in your pictures and this is intrinsically linked to the measurement of light in photography.
If you are not yet comfortable with the measurement of light on your photos or with concepts such as the exposimeter or the dynamic range, don’t worry: you will learn today to master these concepts and a fortiori, the light on your pictures.
The measurement of light in photography
As you probably know, light is an essential element in your photos, hence the importance of getting the perfect exposure to produce fascinating work.
Achieving good exposure means mastering its pillars, which are aperture, shutter speed and ISO sensitivity, which were discussed earlier in a series of articles on learning photography.
But to better understand the measurement of light in photography, I will briefly summarize it:
Aperture : It regulates the entry of light into your camera’s sensor.
You will have to use maximum f-stop apertures for more light to reach the sensor or, conversely, you will have to use intermediate or smaller f-stop apertures for less light to reach the sensor.
The depth of field will be greater or less in your photos, depending on this value.
To know more about this concept, take a look at this article.
light measurement in landscape photography
Shutter speed: This allows you to capture the movement of a scene or, conversely, freeze it, depending on whether you use longer or shorter exposure times depending on the desired result.
But keep in mind that the longer the exposure time, the more light will enter the sensor.
If you want to know how to freeze the movement, don’t miss this post.
measuring light on long exposure photos
ISO Sensitivity: This is the electrical current generated when light enters the camera’s sensor, which gives more information when the light conditions you are working with are unfavorable.
It is therefore the pillar that helps us the most when taking pictures at night or indoors.
But be careful not to use values that are too high as this can cause digital noise in the image.
Law of reciprocity: Exposure in photography
If you control these three variables, getting good metering in photography and exposure is very simple, but how do you balance them correctly for the scene you’re working on?
What is certain is that there are different combinations of aperture, shutter speed and ISO sensitivity that allow you to get a good exposure, which is called the Law of Reciprocity.
In other words, by making different combinations of the three pillars, the result will be the same picture with the same exposure.
The dynamic range for exposure in photography
Before discussing the measurement of light in photography, it is important to look at another equally important concept, namely the dynamic range.
The dynamic range of your camera allows you to obtain details over the entire image, from the darkest to the brightest areas.
It can display the amount of tones in a single scene.
But it’s like everything else: there are exceptions.
relationship between exposure and light metering in photography
Here are some accessories needed to take pictures through the window of an airplane, worthy of a travel agency catalogue.
When photographing backlit areas where one area is very bright while another is completely dark, it will most likely be impossible to show the details of both parts of the scene, so the measurement will have to be taken on one of them.
But it’s essential to know your camera’s dynamic range because the higher it is, the more detail it will be able to capture and the better your work will be.
If you’re looking for sharp shots, you can’t ignore this article.
understanding light measurement in photography
Getting the right exposure
Once we understand these concepts, we must now move on to the light.
When you press the shutter release button, the shutter curtains open and the light that passes through the camera sensor, the amount of light that reaches the sensor is what is known as the exposure.
When the amount is too much, the image is said to be overexposed, while if the light has reached the sensor in insufficient quantity, the image is said to be underexposed.
Our cameras are equipped with an exposimeter that allows us to know the amount of light needed for each work scene.
In the automatic and semi-automatic metering modes, the camera is the one that decides on the correct exposure parameters, whereas if you shoot in manual mode, it is up to you to set the parameters.
To do this, you will have to set the exposimeter indicator to zero by using the previously described pillars: open, speed and ISO sensitivity.
When you open the diaphragm, use a lower speed or a higher ISO and the indicator will move to the positive sign (more light) and vice versa.
Photo of the snow taken with an overexposure of two stops.
Exposure in Photography: Putting it into Practice
Metering is the process of quantifying the amount of light in a scene to obtain a good exposure, thus avoiding under- or under-exposure, or over- or over-exposure of the image.
light metering in photography: overexposing or underexposing
Therefore, if you think it’s time to take a professional photograph, you’ll need to measure the amount of light in a scene using the parameters discussed throughout this article: aperture, shutter speed and sensitivity to make the most of your camera’s dynamic range and therefore capture as much information as possible that is impossible with the correct exposure.
light metering in photography and exposure
If the photo is eventually overexposed, there will be areas of the image without information, due to the excess of brightness.
You can always remedy this in the subsequent editing phase, but the editing software will not be able to invent the lost information.
The same goes for the reverse process: when the image is underexposed, hence the importance of controlling the camera settings.
Exposure Modes in photography
So how to measure the light of a scene to take advantage of the right parameters afterwards? There are three modes of light measurement in photography.
Here is a brief presentation, with explanatory examples for a better understanding:
Matrix measurement: this is the simplest mode of use and the one that works best on most triggers and disciplines.
In this case, the brightness of the whole scene is taken into account.
You should use this mode when you perceive that the entire scene has homogeneous light, such as when working in outdoor areas where the sky is not predominant.
As a general rule, all elements and tones in the picture are correctly exposed.
This is also the ideal mode to play on shadows and lights, but as we saw a little earlier, it will be impossible to get the information from the whole scene, so you will have to focus on only a part of the scene.
Center-weighted metering: This mode works like the previous mode, except that it works in the center of the image.
This mode of light metering in photography takes into account the brightness of the entire scene, but places more emphasis on the center of the scene, so it is ideal for portraits and foregrounds.
It is usually used for photographs where the center of the image is desired to be well exposed.
Spot metering: This mode only takes into account a specific point in the scene.
The closer you get to that point, the more precise the metering will be.
This point generally corresponds to the plane with which the focus was made.
This is the most creative and accurate light metering mode in photography.
It is always a good idea to use this type of measurement, but it also means having more time to work and perform different tests before obtaining the desired result.
understanding light measurement in photography
External photometers for improved light measurement in photography
To measure the light of a scene, you will have to use the photometer of your camera, but be careful because it can very well indicate that a scene is well exposed when it is not, in reality.
You can verify this by doing a test that consists of photographing a sheet of paper.
You will notice that instead of white tones, the sheet will take on grey tones.
This is because cameras tend to neutralize colors.
The most effective way is to use an external photometer and to take the measurement in the brightest areas.
You will then have to adjust the settings based on these areas, so if you make sure that the brightest areas of the image are not overexposed, you will ensure that the darker areas will preserve all the details.
Exposure in photography, step by step
The first thing to do is to configure your camera in manual mode because as we have seen, you will need to take care and have full control over the parameters you will be working with.
And if you opt for manual focus, the results will be more than promising.
Once you know what the composition and the frame of the shot will be, you can set up the light measurement mode that you consider appropriate.
But as we have said, the spot mode is the one that generally gives the best results, even if it takes longer to be applied…
Next, find the point in the scene with the brightest or brightest light and measure at that point.
The settings on your camera then come into play.
Depending on the results you are looking for, you will need to use certain values rather than others.
If you want to capture the movement of clouds, for example, you will need to use longer exposure times than usual, while if you are working outdoors in bright conditions, make sure that the aperture is not the largest to avoid overexposure.
As for ISO sensitivity, it is best to keep it as low as possible to avoid noise in the image, unless the light conditions are very poor.
Once your settings are clear in your mind, you will be able to take the shot.
measuring light in photography
So, you’re going for the light meter on your photos? Put all these concepts into practice and you will notice a radical change in your achievements.
If you also have some tips to share about measuring light in photography, don’t hesitate!
Too much or too little light
It was for a long time a major photographic issue: too much light and the image was overexposed, the whites were toasted, the rendering bland and too little contrast ;
not enough light and the picture was under-exposed, clogged, difficult to read and quickly thrown away .
In film, very small variations in settings have a great impact on the brightness and contrast of a photo.
One passes very quickly from the perfect dosage to the failed image, or even completely illegible.
This is due to the extreme precision of film reaction: chemicals that react to light require a perfectly dosed luminous flux to obtain a realistic image.
Even though digital technology is also very sensitive, it still allows more room for error correction, especially with RAW files.
The cell, the centerpiece
Today, exposure is both the first and the last problem.
The first because it is the basis of the photographic process, and the last because modern cameras excel in this field.
Indeed, cells and electronic chips are almost never wrong anymore.
By letting the case do its job, even a beginner in photography will get a perfectly exposed image in 90% of the cases.
And if a mistake remains, it can often be made up for in the post-processing and printing of the photo on paper.
The nerve of the war is therefore the cell, a set of small sensors capable of precisely measuring the light configuration of a scene.
The modern cells incorporated in SLRs are located in the exact axis of the lens (TTL system: Through The Lens) ;
they therefore measure precisely what the photographer sees in his viewfinder.
There are also external cells, handheld, still used when working with unsophisticated film cameras (medium format, camera…).
) or old cameras – some professionals still prefer this autonomous system to the on-board cells (see below).
All the cells are calibrated on the same basis: medium gray.
It is to photography what the meter is to measure distances or degrees Celsius to temperatures.
The ideal exposure is therefore determined in relation to the light that would be reflected by a gray object in the scene you are photographing.
In reality, it is rare that this type of gray is present in the landscape, but there are often elements that are very similar in terms of brightness, such as vegetation, skin, asphalt, blue sky, etc..
Intelligent programs that analyze the data provided by the camera’s cell are precisely there to permanently simulate this medium gray, even when it is lacking.
Based on this analysis, the camera adapts the exposure by choosing the optimal speed-aperture ratio.
THE SPEED-APERTURE COUPLE
The speed corresponds to the time during which the light reaches the film (or the sensor), and the aperture (or diaphragm) to the size of the hole that lets this light through.
Speeds commonly range from 30 s to 1/4 000 s in automatic mode (and more than 30 s in manual mode, if you use the B exposure which allows you to leave the shutter open as long as you want) for SLRs.
The most common apertures range from f/2.8 to f/22 (see previous chapter).
Four camera modes are available to manage the exposure.
The most elaborate cameras offer all of them, while the simplest (such as compact or entry-level bridges) are mostly in an all-automatic mode, which lacks a lot of flexibility.
Aperture priority (A or Av).
This is the preferred mode for landscape photography.
You choose the aperture yourself (to control the depth of field) and the camera automatically determines the appropriate shutter speed.
Manual (or M).
You manage the speed and aperture yourself, the camera may offer indications on the good theoretical exposure.
To be preferred if you use an external cell or in night photography (pose B).
Automatic program (or P).
The camera manages all the parameters for you according to its built-in programs.
Some cameras also have several Scene programs, depending on the subject (portrait, landscape, sport…).
Especially for beginners.
Shutter speed priority (S or Tv).
You choose the shutter speed and the camera selects the right aperture.
This mode is to be used for slow or very fast exposure.
The question of Dynamic Range
Exposure is not only dependent on the camera, it is also dependent on the sensor used (or the film).
However, both are not only more or less sensitive to light (ISO), they also have other characteristics and limitations.
Among these, the latitude of exposure (or “dynamic”): this is the maximum light amplitude that the sensor (or film) can accurately record, from the darkest to the brightest areas.
Unlike our eye, which can cope with almost any lighting conditions, electronics and chemistry cannot detail both dark and very bright areas at the same time: it is like a singer who can sing either in the bass or treble, but not in both registers at the same time.
The narrowest amplitude is that of slides that begin to lose their rendering fidelity beyond 2 or 3 IL apart (between dark and light).
Color negatives, on the other hand, commonly absorb deviations of 7 EV: this is the largest silver amplitude.
Black and white negatives (4 or 5 EV) and low-end digital sensors (3 or 4 EV) are in between.
This kind of micro landscape, quite simple, is a technical challenge for the dynamics of the sensors or films.
As you can see, it ranges from dense black to sparkling white, through subtle color gradients.
Without a wide dynamic range, shadows would be blocked and unreadable, or whites too bright and overexposed.
WHAT IS THE IL?
An IL is the unit that corresponds to the value of a diaphragm (for example, between f/8 and f/11).
Each time we open the diaphragm a notch, the light passes a little more through the device: it is this quantity of light that serves as a standard of measurement for an IL, like an octave in music.
It is used in particular to quantify the maximum deviation tolerated by the sensor so that the whole scene is readable on the photo.
Let’s take the example of a contrasted scene, containing shadows and brightly lit areas: for the dark portions, the correct exposure would perhaps be f/4 at 1/125 s, while for the bright area, we would rather have f/11 at the same speed.
Between f/4 and f/11, we have a difference of 3 EV, so any camera that has a dynamic range of at least 3 EV will correctly expose all the nuances of the scene.
High-end DSLRs also offer embedded D-Ligthing systems, which also help to increase the exposure latitude from the moment the shot is taken.
These are algorithms that lighten the dark areas of the image as you take your picture.
To evaluate brightness differences, you can’t rely on what you see in the viewfinder of an SLR: your eyes are the perceivers, not the film or the sensor.
On the other hand, what appears on the screen of a digital camera is a faithful basis of what your picture will be, and you can control the balance of the image live.
A limited dynamic can also have its advantages: it becomes a creative process in its own right.
Shadows that turn downright black or sunny portions that turn to bright white can serve your creativity.
For example, shadow effects or intense backlighting can increase the dramatic effect of a landscape.
In any case, you will be led to make choices when the contrast is too important: to privilege the good reading of the dark zones or the one of the bright zones? If the imperative remains that everything is readable, then you will have to darken the light portion (the sky for example) with a gradient filter, or lighten the dark areas with a flash (this is called “uncovering the shadows”, provided that the subject is close and therefore within flash range).
The light temperature
As you know, the light spectrum of the sun is composed of different wavelengths, some of which are invisible to the naked eye (UV rays, infrared, etc.).
Physically, this solar radiation is also different from artificial lighting (bulbs, candles …), which do not have the same vibratory frequency nor the same intensity.
If our eyes do not really make the difference, the film and the sensor are very sensitive.
Thus, the majority of films are designed to faithfully restore natural daylight;
as soon as the lighting of the scene deviates from it, the colors and sensitivity change.
Electric lighting will then give the image a strong yellow-orange or greenish tint if it is neon.
In this case, it will be necessary to increase the exposure time to obtain a correct exposure.
There are also films specifically adapted to artificial lighting, which are very useful for night-time photos of urban landscapes and caves.
Finally, others are specifically sensitive to infrared rays;
their results are particularly aesthetic in black and bench.
Note that color negatives (daylight type) and digital sensors are becoming more and more suitable for artificial lighting, while the slide remains more restricted.
The flashes are designed to reproduce the same color temperature as the sun, which explains the high intensity and whiteness of their flash, as well as the absence of color dominance in photos taken with the flash.
In digital technology, the management of the type of light is done through white balance, which may or may not be automatic – this is the expression used to designate the way in which the electronics will analyze and interpret the perceived light, with the constant concern of restoring it as our eye sees it.
In fact, the camera manages to adapt itself to the type of light present in the scene.
The results are most often reliable but it is not always infallible.
Sometimes the photo will have a strong color cast.
An artifi cial lighting that continues to be processed in daylight, a night scene that turns to blue or full green, a day scene that turns to yellow …
All this is characteristic of a bad white balance.
It is then necessary to select the right light configuration, in the menu of its case, to rectify the shooting.
Depending on the marks, different options are then listed and manually selectable.
Within each option, it is also possible to refine the setting by acting on a slider.
The measurement of light
Accurately measuring the brightness of a subject or scene is one of the fundamentals of successful photography.
This measurement is used to determine the aperture-time couple that will fix the image on the film or sensor.
This conditions the good legibility of the light or dark elements as well as the general atmosphere that will emerge.
Integrated measuring systems
The most complete housings have three integrated measuring systems: Multizone, Center-weighted and Spot.
Depending on the circumstances but also your “affinity” with each system, you can switch from one to the other.
This is the expert mode of today’s cameras, which takes into account the largest number of variables to determine the exposure.
The light is finely analyzed over the entire surface of the image and then compared with an internal database that lists an impressive number of possible configurations ;
A minicomputer then decides on the case encountered and then optimizes the settings.
Each brand has its own technology and vocabulary to designate this mode, but the principle remains the same.
The programs are so sophisticated that they know how to recognize the type of situation being photographed and the position of the main subject.
However, the system is not yet infallible, so you must remain vigilant.
Be aware that the camera almost always looks for the best compromise, a sort of middle ground solution.
In case of strong light amplitude, it is up to you to choose what you want to favor: the high lights (thus the brightest part of your image) or the low lights and shadow detail.
This is a common case in the middle of a sunny day.
Landscapes confront you with strong contrasts and, depending on the time of day, the exposure will be subject to strong variations.
What counts is to build, according to these natural constraints, quite homogeneous compositions.
For example, avoid having gaps of intense light cohabit with large areas of shadow.
If this happens, your Multizone measurement will not be able to work miracles.
It will be forced to make a choice for you or will establish an unsatisfactory average setting.
Center Weighted Measurement
This is the mode of analysis used on the first silver reflex cameras.
It is a global measure of the image which privileges the central zone, where the main subject should logically be located.
Many photographers have made their weapons with this measure;
it is thus found on modern cameras, but it tends to disappear.
If it is not as elaborate as the previous one, at least we know what logic follows the camera.
Indeed, the Multizone measurement is unpredictable in principle because it constantly updates its way of analyzing the image, without focusing on a specific area.
Still, the Center-weighted metering should be used whenever the center of the photo (in the broadest sense) is the reference area for the exposure, such as when photographing a landscape through a hole or window frame.
In these cases, it is useless for the cell to take into account the darker edges of the image, because it is in the center that everything happens.
Be careful, if your key subject is not centered, you know in advance that you will have to make a manual correction, or use the “cropping-framing” technique (see box).
TO MAKE EXPOSURE METERING EASIER: THE FRAMING-REFRAMING TECHNIQUE
This technique simply involves temporarily placing the subject in the center of your viewfinder, locking the resulting exposure setting (by holding your finger on the shutter release button halfway down or pressing the AE lock button), then cropping before you shoot.
Very useful in landscape photography, the Spot measurement allows you to make a spot measurement on a very small area of the image.
You will sometimes have to press a dedicated key to activate it.
On film cameras, a small central circle in your viewfinder shows the diameter of this measurement – just point this circle at the area you’re interested in.
On digital cameras, these are small squares corresponding to the different autofocus selection areas.
Thanks to this, you are sure that the selected Spot zone will be correctly exposed and/or will be used as a reference for the global exposure of the photo.
You can also use this system to check that the exposure values determined by the camera do not deviate too much from the ideal setting for an area that is important to you: you make your Spot measurement on the area that must absolutely be well exposed, and you compare it to the Multizone measurement of your camera.
If the difference is too large, make an exposure correction.
Spot metering is therefore a control tool that allows you to validate or not the choices of Multizone metering.
It is also a creative tool that will force the camera to align precisely to your personal choices.
In short, it is an indispensable measurement mode that will render you many services;
take it into account when purchasing your equipment (especially for film, where not all cameras offer Spot measurement).
The external cell
Some film cameras do not have an integrated measuring system, such as some medium format compact cameras (for example the very interesting Fuji 6×7 and 6×9), some medium format reflex cameras in basic version (for which the viewfinder-cell is optional) and large format cameras.
In these cases, an external cell is essential to properly expose the photos.
Of course, you can also invest in this equipment by choice and preference.
The big difference with integrated cells is that handheld cells allow you to measure the incident light.
Imprisoned in a case, a cell only receives the light reflected by the elements: the sun illuminates the tree, and the tree reflects a certain amount of light back to the camera’s lens.
This is the very principle of color vision: a red object is red because it absorbs the entire light spectrum, except for the red radiation which is reflected back to our eyes like a tennis ball.
Beyond colors, the problem is that some objects are highly reflective and reflect a lot of light, while others are very matte and reflect little – with an initial light source of the same level.
This can mislead the camera’s cell if it sits on an area that does not reflect light in a balanced way.
Snow is a classic example: its very strong reverberation often gives gray, underexposed images in the end.
Therefore, it is often more reliable to measure ambient light at the source (incident light), rather than taking into account light reflected by materials and textures with very different properties.
External cells can also be used in reflected light mode.
To do this, simply remove a small mask and point the cell at the subject.
The most expensive models even have a Spot measurement (with an eyecup for aiming);
There are also spot meters, specifically designed for this type of measurement.
The external cell is therefore a perfect tool to benefit from an incident measurement that escapes all the traps of reflected light.
One is then sure to obtain values perfectly adapted to the ambient conditions of the place where one is located.
On the other hand, the quality/price ratio is rather in favor of integrated cells, which are also more practical and that one does not risk losing or forgetting…
Moreover, the incidental measure is only relevant if you are physically in a place where the same brightness reigns as the photographed scene: this is not always the case, especially for distant landscapes or if you are in a darker area (a tree cover) or more open (in full sun) than what you are photographing.
In spite of the high reliability of the cells, you will often need to check the relevance of the values calculated by the housing, or to choose yourself the area on which to measure the light.
For this, you need to make a voluntary and precise measurement, usually via the Spot function.
The first very classic case is a highly contrasted scene with large differences in brightness.
Given the limited amplitude of the film or sensor, it will be necessary to favor one light register at the expense of the other.
The camera then has three possibilities:
– to be wedged on the darkest zone and to strongly overexpose the rest of the scene;
– to be fixed on the brightest zone and to under-expose the shadows until complete blackness;
– adopt an intermediate setting where only the average brightness will be respected.
Modern programs give priority to highlights, but it’s all a matter of dosage: it depends on the positioning of these zones and their extent…
To keep control of the result, start by choosing the range of light or the element of the landscape which must be imposed.
Then switch to Center-weighted or Spot metering and point to the key area, then take the light metering and store the resulting setting in memory.
Then crop the image to its original composition and compare your voluntary measurement with the values indicated by the camera.
– If there are large deviations (>1 EV), you may have selected an area that is a little too “extreme” for your voluntary measurement.
It may also be a very poor automatic evaluation of your device, but this is less common.
So expect to get a high-contrast picture if you keep your settings.
You can, however, repeat your measurement on a slightly more nuanced area.
To be on the safe side, take a picture with the automatic values just in case.
– If the deviations are small (1 EV), it means that the camera has performed an analysis close to yours.
In this case, opt for bracketing: this involves taking several shots with slight deviations (0.5 or 1/3 EV).
Thanks to this, you opt for safety and one of the images taken will necessarily be well exposed.
The bracketing function is automatic on many SLR cameras;
please consult your camera’s manual to make sure.
Note that it usually takes three shots: one at the initial values, another with a slight underexposure, and another with a slight overexposure.
In practice, this is rarely really useful.
So prefer two levels of overexposure (+0.5 EV and +1 EV), or the opposite if you have chosen to favor low light (-0.5 and -1 EV).
The key to good exposure (in reflected light) is to choose a subject of medium brightness, which is close to the famous medium gray calibrating cells (see page 41).
Here is a list of a few things you may find useful for a well-balanced spot metering.
– In nature: vegetation (foliage, grasses…), the raw earth (field, path, wet sand…), the deep sky (blue without clouds) or dark gray clouds.
– In urban areas: asphalt, street paving stones, brick walls, rough concrete, etc.
– Also think about matte clothes whose colors are not too bright (for example, jeans), hair (brown, red, gray…), and the color of the clothes.
or animal fur (horses, dogs, cattle…) of neutral color (brown, gray…).
Conversely, beware of trap elements that are a source of strong reverberation.
This is the case of dry sand from beaches or quarries (clear, with a lot of silica), snow, bodies of water under the sun, certain rocks and boulders (limestone cliffs, sandstone blocks, white marble, ochre…), white clouds, brightly colored flowers, light-colored buildings (ancient monument, shimmering house, white wall…).
Same for very dark elements, although rarer, such as some black or very dark rocks or some exceptional configurations (opening of a cave overlooking the outside).
When this type of disturbing element is present in your frame, make sure, with a control measure on a neutral subject, that it does not influence too much the global measure of the image.
It is customary to say that in case of strong general reverberation (sea, desert, glacier, snow, Greek village, fog and haze…), the image will be affected.
), a voluntary correction of +1 to +1.5 EV from the indicated values should be applied.
But, in fact, it depends on the weather and the time of the day ;
it is therefore difficult to generalize.
The only ideal solution will be brought to you by an incidental measurement or the use of a neutral gray chart (in reflected measurement).
In case of good weather, a Spot measurement on a background of blue sky (away from the sun) remains very reliable and more practical.
NEUTRAL GREY CHART
This is a small kit made up of grey cardboard boxes of different sizes, sold in photo equipment stores.
This chart will serve as a reference (with a Spot measurement) in the most delicate situations.
In general, remember that it is better to have a slightly underexposed photo than the opposite (the effect is more aesthetic, the colors are more saturated).
On the other hand, in digital photography, an image that is too bright (i.e. overexposed) is easier to recover on the computer at the time of post-processing than a view that lacks brightness, because you will then not be able to restore details that were not recorded when the picture was taken.
Indeed, the digital image, because of its dynamics, has more “reserve” of information in very bright areas than in dark areas.
Certain times of the day and certain seasons greatly enhance or reduce the disturbing factors for exposure metering.
For example, the middle of a summer day is the worst of all configurations, because the brightness is then intense and the contrast maximum.
If we add to this the cohabitation of shaded areas and completely clear areas, the technical difficulties will be real.
Conversely, a late fall afternoon offers a uniform and subdued light: all subjects are softened and exposure is greatly facilitated.
Keep in mind that all exposure problems are related to non-homogeneous and too intense light.
But the most common landscape trap is the strong contrast between the earth and the sky.
How many blue skies have changed into milky white (because overexposed) on the photo? To rebalance this difference in brightness, without waiting for a more favorable time, a neutral gradient filter must be used.
Dark gray in its upper part and transparent underneath, it darkens the sky and delivers a more homogeneous image, usable by the sensor (or the film).