In this article we will talk about the focal length of a lens. A great unknown for most beginners, and a (fundamental) ally when you know it.
I will explain what focal length and angle of view are, the differences between the different types of lenses according to their focal length and in which situations it is convenient to use one or the other so that you can get the most out of them.
You can’t miss it! Be prepared, it’s a long article. Mind you, I’m going to make it as simple as I can, but very complete, so you’ll have all the information in one package. You’ll want to save it to come back to it more than once.
Focal length is the distance between the optical center of the lens, and the sensor or focal plane onto which the image is projected. It is also known as “focal length”, and is measured in millimeters.
In photography, the longer the focal length, the more “zoom” the lens will have, and the less of the scene it will capture. The shorter the focal length, the “farther away” things will look, let’s say, but the framing or angle of view will be much wider instead.
Better to see it with the following examples, same scene, from the same position, with different focal lengths.
Example of focal length
To continue to avoid getting into too many technicalities, the focal length is not measured from the sensor to the front lens of the objective, but is measured from the point where the light rays cross inside the objective and are directed towards the sensor.
Such a point is very close to where the diaphragm is located and is called the optical center.
Optical center of the objectives
How is focal length (or focal length) measured?
Focal length is measured in millimeters (mm), the longer the focal length (larger the number) is said to be a long focal length, it brings us closer to the subject and covers less scene. The shorter the focal length (smaller the number) the more scene it captures.
So that we understand each other: a focal length of 70mm means that the lens is able to bring us closer to the photographed subject much more than a lens with focal length of 18mm and will show less part of the scene.
And a 200mm will have even greater ability to get closer to the subject, reducing the part of the scene that will be photographed.
Effective focal length
The focal length of a lens, whatever the make or model of the lens, used as a reference to the sensor size of a Full Frame (35mm) camera.
Why is this important? Because according to the sensor size of your camera (Full Frame, APS-C, 4/3, etc.), the effective focal length of the lens will vary.
If you have a camera with an APS-C sensor that is smaller than Full Frame or Full Format, such as a Canon 700D or a Nikon D3100, a 50mm lens on those cameras will be equivalent to a 75mm if you use Nikon or 80mm if you use Canon.
Why? The focal length of a lens depends on the sensor size of the camera on which it is placed and since the APS-C sensor is smaller than the Full Frame standard, to know the effective focal length, you must multiply the original focal length by a multiplication or crop factor.
This factor depends on the brand (due to the size of the sensor), for example, for Nikon it is 1.5 and 1.6 for Canon.
How is the multiplication factor calculated?
Just as a fun fact, if you want to know how the multiplication factor (also known as conversion factor) is calculated, the following formula applies:
Full Frame sensor width (35mm). / Sensor width of your camera
If you don’t know what the sensor width of your camera is, you can check it on the camera manufacturer’s website.
It is usually expressed as follows: 23.1×15.4mm. The first part (23.1mm) being the width of the sensor.
How does the crop factor affect your photographs?
This is of more interest to you. Imagine you purchase a lens with a focal length of 16mm because you intend to go on a trip and portray some amazing landscapes, but your camera has an APS-C sensor: the distance
effective of the same will not be 16mm but 24mm (being a multiplication factor of 1.5).
Result: The lens is as angular as you might have imagined and the angle of view of the lens (I will now explain what this means) does not allow you to capture the same portion of scene that you would capture on a full sensor camera.
Let’s look at an example we have extracted from Nikon’s simulator (more about it below): same scene, from the same place with the same 24mm focal length. The difference, one is taken with a Full Frame sensor and the other with a DX sensor (that’s Nikon’s name for the sensor smaller than the Full Frame sensor).
24mm with DX sensor
24mm with full frame sensor (Full Frame)
You might see it clearer this way, I have marked you, approximately, the portion of scene that the cropped format (DX) captures compared to the full format (Full Frame):
Comparison of scene with full sensor and cropped sensor.
The effect, apparently, is as if you were zooming in,
but it’s not really like that. It’s not that the lens zooms in closer on a smaller sensor camera. It’s more of a cropping effect, as if you had the original photo taken with a full sensor as the original photo and in editing you crop it along the dotted line.
Let’s see what types of targets there are.
Mainly we can make two classifications,
according to focal length and if this is fixed or variable.
We will first delve into this last point, below, we will discuss the classification according to their focal length.
Normally, most of the lenses that come in the camera kit are lenses with a
variable range focal length.
That is, they are lenses that normally present a focal length ranging from one value to another.
For example, it is very common to find objectives of
variable focal length, a 18mm to 200mm.
This means that the lens has all that range and that we can regulate it as we wish, using from a very high value such as 200mm, if we want to get close to a relatively distant object; to a much smaller value of 18mm, if what we want to capture is a complete framing of a panoramic scene, landscape, etc.
There are also lenses on the market with
fixed focal length, ie, that you can’t zoom with them, they always work at the same focal length.
Those of you who read this blog regularly know how in LOVE Mario is with the one he calls
King of Lenses, the 50mm f/1.4. If you want to know the supernatural, almost magical properties of this king of lenses click here.
Fixed or variable focal length lenses?
But… which one to use, fixed or variable focal length?
Each type of lens, whether fixed or not, has advantages and disadvantages. Therefore, choosing the ideal one will depend on your tastes and needs as a photographer.
Here I leave you a small analysis of advantages and disadvantages so you can evaluate which type of lens is the one you prefer.
Fixed focal length lenses
Those that do not vary in focal length. They can be, for example, a 35mm or a 50mm, such as the
king I mentioned earlier.
Advantages of fixed focal length lenses.
Higher optical qualitywhich translates into more sharpness in your photographs. They are constructed with fewer moving parts, so they tend to be.
more resistant and robust. Being optimized for their focal length, they produce.
Higher brightness which will allow you better shots in low light conditions and shallower depth of field when working with wider apertures (f/1.4, f/1.8, f/2.8). They usually also offer bokeh very nice. Many of them are
more economical than the variable versions.
less versatile since as we have said their focal length is fixed. Anyway, this can be seen as an advantage, since they will force you to move around the whole scene to get the perfect framing. Although for certain types of photography, the lack of versatility can be a real problem. Zoom or variable focal length lenses
Advantages of zoom lenses
They are very
versatile, comfortable and will allow you to adjust the framing without having to move around. They are indispensable for certain types of photography where you need more focal range, such as nature or sports photography.
in a single lens a large number of focal ranges. so you will avoid constantly changing lenses on your camera, gaining speed and avoiding shocks and dust on the lenses and the sensor of your camera.
They are usually quite
more expensive than the objectives primeespecially those with a long focal length such as an 18-200mm. Having a much larger number of moving parts, they are.
more fragile to any blow or accident. Your
weight and size is considerably larger. They are
less luminous, especially at the longer focal lengths.
Canon prime lenses Mario’s experience with fixed and variable focal lengths.
“My first camera was a Nikon D60It came standard with two lenses: an 18-55mm and a 55-200mm.
At first I was glad, I thought “this way I have an additional lens, two lenses will be better than one I say…”, I still had that mentality of the more things the better, the “ansia viva” as Mota would say.
But after a short time I realized that going on a photographic excursion with two lenses was not the most practical thing to do, since I had to change lenses every few days. I began to notice that there were people who had only one lens ranging from 18 to 200mm, just one, so I thought “How practical! you don’t have to remove one and put another one every so often”.
I made the determination to sell my two lenses and by adding a little money buy a single lens that had the widest focal length range (18mm-200mm).
After some inquiry I changed my mind again. Since then I have kept the two different lenses (plus others that I bought). You may ask why?
A lens, to put it very simply, is nothing more than a tube with a series of glass lenses inside. Those lenses are made in the best possible way to take the best pictures for the focal length for which that lens was designed. The wider the focal length range, the more difficult it will be to get the best pictures for the focal length for which the lens was designed. ” perfect. It is as if it were a matter of specialization: an 18mm-55mm lens is specialized in that range and will therefore take better pictures than an 18mm-200mm lens. Mario’s golden advice
Buying a single lens with a lot of focal length range is not the end of the world either, you can still take decent pictures with it (remember who takes the pictures?).
It also has the advantage of making it easier to have it all in one lens, but if what you’re really worried about is getting
a quality photographand you are willing to spare no effort to achieve it, then, dear reader, it is best to have several lenses with short focal lengths or fixed focal lengths.
Thus, each lens will have its use and its moment. The greater the specialization, the better the performance.
Lenses and angle of view
Having clarified the fixed or variable focal length issue, we return to the focal length, and this is not the only element that you should take into account when evaluating a lens, but you should also pay attention to the
angle of view of the same.
In this way you will be able to understand the different possibilities that will allow you to exploit a certain lens when taking your photos with it.
The angle of view is something like, the “portion of the scene” that the lens can capture of it, but measured in degrees.
The more angular the lens is, the larger portion of the scene it will allow you to capture in a single photograph (wider angle), and the more zoom or tele the lens is, the smaller the portion of the image you will be able to capture in a photo (narrower angle).
For example, a 300mm focal length lens (effective focal length) offers an angle of view of approximately 8.15°. So if you use one, you can fill the entire sensor with a much smaller portion of the scene (zoom feeling) than if you use, for example, your camera’s kit lens at 18mm (76º angle of view), where the same portion of the scene would occupy a much smaller size in the frame.
64°30′ (18mm) angle of view.
Angle of view 9°30′ (135mm).
While lenses are classified and marketed according to their focal length, what is really important is the angle of view of each lens.
Anyway, to each angle of view corresponds a focal length, so if you know both factors well it is almost like talking about synonyms.
In the following graph, you can see the relationship between the angle of view and the focal length of a lens:
Relationship between focal length and angle of view.
If you want to see how this works in practice but don’t have enough lenses to try it yourself, I recommend you take a look at the.
lens simulator that Nikon put at your disposal to perform all the tests you want, without spending a penny.
In this article you will be able to see how such a simulator works.
Classification of lenses according to their angle of view
Since we know what the angle of view is, let’s now see what is the classification of lenses according to it, first a graph, for a first visual approach, below I describe them one by one.
Super wide angle
These so-called “fisheye” lenses can cover an angle of view 180° or even more and are those with focal lengths below 8mm.
Urban scene in 4mm Wide angle
These are those lenses that cover an angle of view between 110° and 60°, which would represent an effective focal length between approximately 10 and 25mm.
Landscape in 16mm Standard
These are all those lenses that cover an angle of view between 60º-25º. Their focal length is between 25 and 65mm, approximately.
Portrait at 50mm Short tele
They are those that cover an angle of view from 25º to 15º. We are talking about a focal length between 65 and 100mm.
Love in 85mm Telephoto lenses
They cover an angle of view of 15° to 10°, corresponding to a focal length of 100 to 160mm.
Cycling in 200mm Super telephoto lenses
Those covering an angle of view from 10° to 1°, reaching up to 600mm focal length.
Focal length and distortion.
Lenses, as a function of focal length exhibit more or less distortion.
The ones that most closely resemble the way our eyes see are the standard ones. However, telephoto lenses, for example, compress the planes, in addition to causing greater blur.
The more angular ones offer greater depth of field, but also cause a lot of distortion of lines and in faces.
Let’s look at an example of this, the subject is the same, our friend Mario, but what about his face and body, notice the shoulders in the different images. Look also at the background.
Comparisons of different focal lengths and their distortion.
detail is also important when choosing which lens to use at any given moment, as it will influence the final result.
Now that you are well clear on the fundamental technical aspects regarding lenses, it’s time for you to see what type of photography each one is ideal for, although with the examples from before you may have already got a slight idea 😉 .
A lens for every occasion
While you can do almost any type of photography with any lens, each of these is designed for a particular use.
For example, although you can shoot a portrait using a wide-angle lens, you will get better results if you use a short 85mm telephoto lens that allows you to blur the background, bring your model into focus and present less distortion.
If you want to get the most out of your lenses or you are about to buy a new one, you need to be very clear about the situations in which you will get the best results with each of these, or in other words, what you will use them for.
Lenses according to ideal photographic types.
There are various types of focal lengths that can be useful to you for close-up or macro photography.
At the end of the article I will explain which ones I consider the most convenient.
Lenses for landscapes
For this type of photography you will need to fit as much of the scene as possible into a single photograph. The goal is to be able to transport the viewer into the image, to make them walk through it and feel like they are in the place.
The more space you want to show in your photographs,
the wider the angle of view and, therefore, shorter focal length the lens to be used must have. Therefore, a wide-angle lens (focal lengths shorter than 25mm in APS-C) becomes the most recommended option.
Now that you know what kind of lenses you will get the best results in landscapes and before you start going out to take pictures, I recommend you take a look at the following article to transform beautiful landscape photos into spectacular images.
Only with a wide-angle lens is it possible to take such a large portion of the scene in a single photograph.
The focal range you are going to use in the world of social photography will depend on the type of shots you have in mind and the situations where you plan to shoot them.
Covering a wedding is not the same as shooting portraits in a studio where you can take the time to change lenses according to the need of the moment.
In any case, if you plan to shoot close-ups, the ideal is to work with long focal lengths.
That is to say, to have a telephoto lens.
However, for full body shots you will need shorter focal lengths and larger angles of view, so with a standard lens you will be in a position to do wonders.
In this type of photography it is not easy to choose between one or the other focal length, as each has its advantages and disadvantages.
What you need to be clear about is what kind of pictures you expect to take and decide what angle of view (or focal length) you will need to take them.
Feel free to take a look at the following articles where each social photography topic is discussed in a more specific way.
Wedding photography with standard focal lengths
In this type of photography it is not necessary to take a large panorama showing the whole environment (unless this is what you are looking for and you require a wide angle lens) but rather the opposite: to focus the viewer’s attention on a given moment.
Always depending on how close you can get to where the action is taking place, the ideal choice for this type of photography is to have a short tele or telephoto lens that allows you to be close to the action, but keep your distance.
Although fixed focal lengths offer superior quality to those lenses with variable focal length, the latter will give you much greater versatility, since you can shoot using one or another distance according to the situation you want to portray.
A 70-200mm or a 70-300mm can be ideal allies.
Beware of extremely versatile lenses such as the 18-200mm as, while they avoid having to change lenses often, your photos will be less sharp and therefore you will sacrifice a lot of quality, for convenience.
Getting this close is only possible with a telephoto lens.
Lenses for adventure photography
Adventure photography is where you will require lenses with longer focal lengths.
Whether it’s to portray a bird in mid-flight, a soccer player scoring a goal, a race car rounding a bend or a lion stalking its prey in the grasslands, the distance you can get to position yourself from your subjects is very considerable.
The recommended focal length for this type of photography starts at 100mm and can go up to 600mm.
Of course, as long as your budget allows you to access such expensive optics.
Anyway if your camera is APS-C (sensor size) don’t forget that, at 200mm you will have to multiply it by its factor (1.5 in Nikon and 1.6 in Canon, Pentax, etc.) to obtain its effective focal length, which will be greater as the sensor size is smaller with respect to Full Frame.
The farther away you are from the subjects or objects you want to portray, you will need to have longer focal length lenses to achieve mind-blowing close-ups.
I recommend, if possible, having a lens with variable travel such as a 70-300mm to allow you more versatility.
Keep in mind that, at
the longer the focal length, the greater the risk of blurred photos due to camera shake, so having a stabilized lens will allow you to shoot at slower speeds and work in lower light situations than one that is not stabilized.
Taking a photo of a bird without scaring it away thanks to a super telephoto lens.
Lenses for macrophotography
As in adventure photography, distance to subjects is critical.
But, in this case, you’ll want to be close enough to be able to fill the frame with an insect and far enough away from it so as not to scare it away.
This is why I personally recommend that you use macro lenses of the longest focal length possible.
This way you will be able to magnify the scene without interfering with it too much.
There are countless macro lenses on the market with various focal lengths and all of them can be useful, depending on the type of subject or object you plan to photograph.
For product photography, for example, you can use a 40mm macro focal length as it is unlikely that a watch will fly out of the scene.
On the other hand, if you want to photograph a bee collecting pollen from a daisy, it will be almost impossible with a short focal length as you will scare the bee away.
The focal length to use in macro photography
will depend on the type of subjects or objects to be photographed and the distance you can stand from them. Take a look at the following article if you want to master macro photography.
Spectacular macro photography
While you can take pictures with almost any lens, since the camera is just a medium and the magic happens in your eyes, having a good lens designed for a particular purpose can make your job much easier.
You don’t need to spend all your savings on the most expensive lens of the most recognized brands, there are endless “alternatives” that can even give you better results.
If you don’t believe me, take a look at the following article: “Second-rate brands? No… 13 Top Targets!”.
After all, the key is and always will be: take pictures! If you have any questions, leave them in the comments and we’ll answer them as soon as possible, and if you found my article useful, spread the word, I’m sure someone else will find it useful. Thanks and see you next time.
💡 Thinking about buying a lens? Don’t miss our guide with all the tips when buying one and our best recommendations.