About Depth of Field

For the photographer, taking a picture is more than point & shoot. It is the work of creating an image of a subject that will make the viewer see what the photographer wants them to see, using different techniques to highlight the subject (or the subjects).

One of the tools in the photographer's toolbox is Depth of Field (DoF), which is the parameter that will define the part of the picture in focus, and the portion out of focus (blurred).

Hummingbird Portrait 7 by ©Danny Perez Photography

In the above photograph, the DoF is very shallow: almost only the bird is in focus, and the background is so blurred it is hard to know if it is grass, bushes, trees, or a piece of green cardboard!

DoF: measure it? Calculate it!

To be more precise, the Depth of Field is the zone within the focus near limit and far limit: everything before the near limit and after the far limit is considered out of focus. Yes, the DoF is actually a distance! Ok, maybe you were already aware of it. But did you know you can calculate it? Physicists and Mathematicians are amazing. They have built a model to calculate, or rather make an approximation of the DoF. Here it is:

Where

• D is the distance between the camera and the subject (m),
• H is the hyperfocal distance (m).

The formula to calculate an approximation of H is:

Where

• f is the focal length (m),
• N is the f-Number (no unit),
• c is the circle of confusion for the film/sensor of the camera (m).

In any given situation, with these formulae, you can calculate the DoF, pretty interesting, uh? Sorry for the Maths, but it is solely for the sake of explanation. I bet you don't want to calculate DoF with the formula by yourself; luckily, there are several websites which offer to do the calculation for you, here are a few examples:

• fcalc.net can calculate DoF among other interesting things,
• dofmaster provides a nice DoF calculator and other useful stuff.

Manage DoF

Depth of Field is essential in a phtograph, you definitely want to manage it. How? I will help you out, by analyzing the formula from the previous paragraph.

Many parameters appear in the formulae, let's have a look at them:

• D, the distance between the camera and the point you set focus on. You can change this parameter by moving or by making the subject move, but this will obviously have an effect on composition,
• f, the focal length, can be changed either by setting it on your lens or by switching lenses (if you have more than one). This will also obviously have an effect on composition,
• N, the f-Number, is the most easy parameter to change, you just have to set it on your camera (if available). It determines how wide the diaphragm opens. This has an effect on how much light is transmitted to the film/sensor (the greater the f-Number the less light is transmitted),
• c, is a constant determined by the size of the film/sensor. Thus it is not possible to change it (except if you use a different camera).

Jonquil flowers at f32 by ©Fir0002

Jonquil flowers at f5 by ©Fir0002

Out of 4 parameters, 3 can be easily changed: let's focus on these elements and take a real situation as a case of study.

You own a Canon 1DX camera (yes, you are rich!!) and a EF 24-70mm f/2.8L USM lens. The sensor has a circle of confusion of approximatively 0.03mm (0.00003m).
You want to take a picture of a bird on a tree with bushes behind, which is 4m away. At first, you set the f-Number to f/4 and the widest angle available by setting the focal length to 24mm (0.024m).

In the start situation, using dofmaster's calculator, you know you have a DoF of about 21.1m. That means the bird, the tree and probably the bushes will appear sharp on the photograph no problem.

Now, go 2 steps back, let's say one meter. You are now 5m from the bird, the DoF is infinite and all the landscape is sharp!
Go 4 steps forward, you are 3m from the bird, the DoF is now 6m and the bushes are a little blurred.
Go 2 more steps forward and (2m from the bird), if the bird did not flee, the DoF is now 2m and even the tree is not sharp everywhere.
As you can see, the distance to the subject can change the DoF a lot. The closer to the subject, the more shallow the DoF.

Let's go back to the start situation. The DoF is 21.1m.
Instead of stepping forward, we want to zoom in using the focal length. We increase the focal length to 48mm, and the DoF falls down to 1.72m! Goodbye background, bird is the center of attention.
When you think about it, stepping forward or zooming in have the same influence: the subject seems closer. Same conclusion as before, the closer to the subject, the more shallow the DoF.

Back to the start situation. You want to play with the f-Number now.
Let's set it to 5.6 (one stop): the DoF is now infinite.
Set it to 2.8 (one stop the other way): DoF = 7.1m.
The lower the f-Number, the more shallow the DoF.

As you can see, these three parameters have a great influence on Depth of Field. But nothing comes without a counterpart.

Consequences

By reading the following paragraph, one might want to conclude it is easy to adjust the DoF: simply change the f-Number! Unfortunately, nothing is simple and photography is a matter of balance.
You can increase the f-Number to increase the DoF, this is right. The counterpart is less light will be transmitted to the sensor. To keep a good exposure, you will have to either increase the exposure time or the ISO: the first will result in possible motion blur (which is neither good or bad but changes the picture), the second might add noise. Not to mention if you are in a low light situation, you might want to use as much light as possible. See? Not that simple.
Moving forward or backward from your subject also changes the DoF, but it changes the composition in a strong way, so does focal length adjustment.
Worse, lenses do not provide the same image quality for every focal length and every f-Number. Got a headache yet? Calm down. In a given situation, what you want to think thru is: what result do you want to get?

Then what do you need to do? Experience! Try things out, get to know your gear better, explore. Theory alone is meaningless.

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Rule of thirds

As a beginner in photography, it is frustrating when you see something gorgeous, but you can't capture the beauty the way you see and feel it. Many things are important to take into account, like configure your camera to fit your vision, the angle of the camera, lights, etc.

Composition is one of these concepts that matter. The first reaction you have is to put the main subject in the middle of your photo. Most of the time, it is not that great of an idea.

The rule of thirds appeared in painting first, and has been used in photography since the beginning. It is a rule meant to help you highlight parts of the scene you want to immortalize.
Take your frame, split it in thirds horizontally and vertically, drawing two lines in both directions. Now if you want to highlight subjects on the scene, the rules says you can place the subject at an intersection of two lines. It's very simple, you just have to get used to it and have some practice. The main question you need to ask yourself is "what do I want to highlight?".
When you imagine these lines, you can also use them to superpose other lines on it, such as the horizon, or imaginery line that would join two or more points of interest (eyes, shoulders for example).

You do not need to apply this rule, and composition is much more than this rule alone. But you should definitely try ut and you will see many of your photos will look better this way.

Here are various photos to illustrate this composition rule.

Rule of thirds by ©Alan Cleaver

rule of thirds / pattern by ©Maurice Johnson

Posing white tiger by ©Tambako The Jaguar

Candle light by ©Gabriel Tran

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A word about white balance

You may have bought yourself the best digital camera in the world, yet if you don't understand white balance, some pictures might result in bluish people, redish colors, in other words "wrong" colors. I am sure you have seen pictures like this.

What happens? Why does your camera renders pictures this way?

Lily-M7292-As-shot-and-manual.jpg by ©Fg2

White Balance

White Balance is the adjustment that corrects colors seen by the camera so that white (or neutral colors) is actually rendered white. This sounds trivial, why would white appear not white?

Possible causes

I see two answers to that question.
First, the lighting. All lights do not have the same color: we call that the "temperature". For example, an incandescent light bulb usually spreads a warm light. A candle burns with an even warmer light. Although human eyes may still recognize the "true" colors, the lighting changes the way colors are seen, and cameras may not render a scene the way you felt it.

Second source of errors is the influence of surrounding colors. Take a neutral grey pair of jeans. Wear them with a blue shirt, and blue shoes. Ask a friend what color are your pants. Come back a few days later (after you washed it) with the same pair of jeans, but wear red clothes. Ask the same friend what color your pants are. They might be good and recognize the pants, but they might see a different colors of pants!

How to adjust White Balance

Fortunately, nowadays cameras are smart, although they cannot compete with our eyes. By default, cameras are set to auto white balance, which means they handle the white balance by themselves, figuring it out from what they "see". In natural light (sun, moon), most photos should be OK with this setting.

There are other settings. Depending on the scene's light, you can select presets to fit with it. Most common presets inclue Tungstene, Fluorescent, Daylight, Flash, Cloudy, Shade. All these settings represents different situations with different temperature of lighting.
Some cameras allow more accurate settings by letting you choose the temperature directly. I don't want to go to far in the details, I let you visit other articles for precisions (see end of this note) on temperatures. Just know candle light is about 1000K to 2000K and shade can go up to 9000K to 10 000K.

Whitebalance4.jpg by ©By Thomas Steiner [GFDL], via Wikimedia Commons

Another interesting option is custom white balance. When present, this setting lets you give a sample of a neutral color, to be used by your camera as a reference. This is the most accurate possibility, if your reference is good.
I don't know how it works on all cameras, but on my Canon 500D, I take a picture, display it on the screen, go in the menu and select custom white balance. As easy as that. The only difficulty is that your reference photo should be taken with same lighting condition as your subject.

Last chance to set a correct white balance is by processing your RAW. Yes, you need to take photos in RAW format (you should always do!). All good software which handle RAW files can change the white balance of the picture. I find it impressive to be able to do that after the photo was taken!

Remaining problem

There is a remaining problem. What happens when you want to take a picture of a scene with different light sources? For instance if you take a scene with a subject on the foreground enlightened with an artificial light, and a background which has a natural light? A problem, that's what! With your camera, it is not possible to correctly render all parts of the photo, you need to choose which part you want to focus on (or if a camera can do both, please let me know!).

More

These articles will tell you more about white balance:

• Color balance on Wikipedia
• Introduction to white balance on digital photography school
• Tutorials: white balance on cambridgeincolors

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Sensitivity to light and ISO

Photography is all about capturing light on a medium (film, sensor, ...). This medium has a sensitivity to light, meaning it needs more or less light coming in to catch successfully a scene.

What we simply call "ISO" refers to a standard of light sensitivity measurement, managed by the International Organization for Standardization (ISO - based on the Greek word isos), or should I say several standards (ISO 5800:1987 for color negative film, ISO 6:1993 for black and white negative film, ISO 2240:2003 for color reversal film, ISO 12232:2006 for digital sensors). Let's keep it simple and stick with "ISO".

A film has a static light sensitivity, a single ISO value, whereas sensors used in digital cameras can change sensitivity and offer a range of ISO values; ISO usually take values from 25 to 6400, but it can start lower and go higher.

How does that influence your photographs? A change in light sensitivity simply means that with a given amount of light let in, the photo you take will appear brighter if the medium is highly sensitive to light (high ISO value), and darker if the medium is less sensitive (lower ISO value). Yes, it means if you work in a dark environment, such as at a concert, you will probably need to select an ISO value of 1600, 3200 or above, and if you take photos in intense light, by a sunny day for instance, you might want to work with low ISO.

Below are images taken in the same environment, I just changed ISO value so you can have an idea of it's impact on image brightness.

By ©Gabriel Trần

There is more to it: high light sensitivity medium produce grainier images, which can be interpreted as lower image quality, or as an artistic effect. Note that this noise is not the same on every medium: two camera sensors at ISO 3200 can have different noise levels.

Fortunately for us, nowadays sensors have very reasonable noise even at high ISO, as you can see below:

By ©Gabriel Trần

Now you have one key to well exposed photographs. Don't hesitate to go to high ISO values, as you can see noises are not that terrible!

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Photozone: technical reviews

Photozone.de is a website for technique, diagrams and figure lovers.

The website is filled with complete and technical reviews of lenses and DSLRs, and you can see for yourself there are a lot of them, enough to give newbies a headache!
Don't worry, you can find the definitions needed to understand the reviews by searching the website.

Klaus Schroiff has written many articles to explain the basic and less basic concepts of photography. A very resourceful website!

Pentax K-7 size comparison by sveinmb

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A few answers for beginners

Did you know about 5 millions digital camera have been sold In France last year? Even though this statistic includes mobile phones with embedded camera, the digital photography market is expanding.

As a beginner, it is difficult to enter that world made of electronics, optics, computer science.
To help you understand the basics of digital photography, the lizard suggests the article 20 questions and answers for new photographers from photo tuts+.

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