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Beginners Guide to Camera Lenses: Parts, Functions and Types

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Without a lens, your camera body would not be able to capture images.

Choosing the right lens is important because it helps you to reach the maximum capacity of your camera. Without a good camera lens, you will see a loss in image resolution and quality.

Read our camera lens guide to find out all the information you could know about lenses.

an image if several camera lenses set next to each other in ascending order by size

Is a Camera Lens More Important than the Body?

Camera lenses, like it or not, are the most important part of your kit.

A camera lens denotes the aperture range you can use, the possible depth of field, and the focusing distance.

Camera bodies allow other settings such as ISO and shutter speed. They influence the quality of the image through resolution. But they are not as important as lenses.

Usually, your lens is not able to resolve as much information as your camera can provide. The quality of the lens determines how much detail it can manage. You can have a 40-megapixel camera and still not be able to take advantage of it. Generally, it’s better to buy an expensive lens for a not-so-expensive body. This way, you can maximise the image resolution.

an image of a fujifilm camera and four lenses

The Anatomy of a Camera Lens

Lens elements are shaped glass pieces that bend light in specific ways. Each element has a different function, and they work together in harmony.

Some of these pieces are fixed to the barrel of the lens, and others are movable. These allow you to zoom, focus, or assist in image stabilisation.

an infographic explaining the parts of a camera lens

What Is Focal Length?

When light travels through your camera, the image is flipped upside down. This is the same way our eyes see the world. In our case, our brain rotates the image.

an infographic explaining how a dslr sees an image

Inside the camera is a pentaprism that flips the image the right way up. As you can see, there is an intersection inside the lens. This intersection is the convergence between the lines of light that we get from our subject.

an infographic explaining how an image is flipped by the pentaprism

In optics, this crossing point is called the ‘point of convergence’. The distance between this point of convergence and your image sensor or film is the focal length.

an infographic explaining focal length

Why Is Focal Length Important?

The focal length of a lens determines its field of view. This is what makes a lens wide, standard, or telephoto.

Consider the placement of the point of convergence. The closer it is to the imaging sensor, the smaller the object appears.

an infographic explaining 25mm of focal length

Imagine the point of convergence was much farther away from the imaging sensor. This would make the subject seem much larger.

As you can see, a short focal length creates a wide field of view. Lenses with a shorter focal length are known as ‘wide angle‘ lenses.

The opposite is also true. A long focal length creates a narrow field of view. These lenses are known as telephoto lenses.

How Do Crop Sensors Affect Camera Lenses?

The film plane in 35mm film cameras came in one size. This 24x36mm hole allowed the film to be exposed correctly. Nowadays, with digital cameras, these sensor sizes have quite a range.

Here, we will be talking about how the size of the camera’s sensor affects the cropping of your scene.

What is the Crop Factor

You may hear the terms full-frame, 35 equivalent, APS-C, or cropped sensor thrown around. The big difference is what you are actually capturing from your scene.

A full-frame or 35mm equivalent is the same thing. If a camera is listed as a full-frame, it has the same size sensor as 35mm analog cameras: 36x24mm.

APS-C,  Micro Four Thirds, and 1” sensors are all cropped when compared to a full-frame sensor

  • APS-C (except Canon) has a size of 25.1×16.7mm. To get to 36x24mm, you need to multiply the number by 1.5. This gives APS-C a crop factor of 1.5x.
  • APS-C (Canon) has a size of 22.5×15mm. To get to 36x24mm, you need to multiply the number by 1.6. This gives APS-C a crop factor of 1.6x.
  • Micro Four Thirds (MFT) has a sensor size of 18×13.5mm. To get to 36x24mm, you need to multiply the number by 2. This gives Four-Thirds systems a crop factor of 2x.

The way a crop sensor works is that it magnifies the focal length of the lens. A 35mm lens becomes 50mm with a Nikon 1.5x crop factor.

A diagram showing the difference between 2.0 crop factor, 1.6 crop factor, 1.5 crop factor and 35mm full frame

Difference Between Zoom and Prime Lenses

Whether wide-angle, standard, or telephoto—every lens falls into one of two categories; zoom or prime.

Zoom lenses allow the point of convergence to move closer or further away from the sensor.

A lens with a fixed focal length is a prime lens.

The complexity of zoom lenses results in quality loss. Also, they do not allow you to open your aperture as wide as prime lenses.

You must spend more on a zoom lens with the same image quality and brightness as a prime lens.

an infographic explaining zoom range between 25mm and 50mm

Lens Aperture

Aperture is another reason why photographers choose one lens over others. The word aperture means opening, hole or gap, and describes the size of the aperture ring of a lens.

This is where the light passes through, making its way to the camera sensor. Aperture works like the pupil in our eyes. They both control the amount of light getting into the camera or the eye.

Aperture numbers are a fraction of the aperture diameter and the focal length of a lens. We see f-stops written as f/2 or f/11.

If you are capturing a scene with a 100mm focal length lens at f/2, the diameter of your lens is 50mm across.

The f-number gets bigger, but the aperture gets smaller. An f/2 value is bigger than f/4, which is two stops brighter than an f/8.

How Do Apertures Affect Lenses?

When it comes to choosing a lens, the most important factor is the maximum aperture. This number is written on the lens and included in its specifications.

The biggest-size aperture is an expression of how ‘bright’ the lens is. Brighter is better.

Often, a lower f-number means a better image quality. For instance, you can expect an f/1.2 lens to outperform an f/1.8 lens in terms of resolving power.

What is Variable Aperture?

Variable apertures are different maximum apertures (smallest f/stop) that your lens will use. It depends on the amount of zoom you use.

Aperture can cause some obstacles when it comes to zoom lenses. Let’s use a 70-300mm f/4-5.6 lens as an example. At 70mm, you can use the f/4 aperture. 70 divided by 4 is 17.5mm.

By zooming all the way in, we go from a 70mm to 300mm focal length. The images you capture are magnified by 4.3%. At 300mm, your maximum aperture is f/5.6, where the diameter is 5.4mm.

But why cannot the lens be f/4 throughout the zoom range? At 300mm, an f/4 aperture would be 75mm. This is too big to fit into the slim body of the lens.

Many photographers see these lenses as inferior and avoid them. These lenses offer more variability, but they have their disadvantages too. Generally, you sacrifice image quality.

Non-variable aperture lenses offer some significant advantages. They have a better image and build quality than their counterparts.

A chart showing how aperture and depth of field correspond

Camera Lens Markings

The numbers you will find on a lens are all very important. The first number is usually the lens’ focal length. This number is represented in millimetres.

If you see one number rather than a range, it means its a prime lens. It could say 24mm, 50mm, 85mm, or something similar.

A focal length range will have two numbers separated by a dash. 24-70mm is a good example.

an closeup image of a 50mm camera lens focus ring

The second number you will find on a lens is usually the lens’s maximum aperture. If you have one number, it means your zoom lens has a fixed maximum aperture.

Prime lenses do not have a variable maximum aperture.

If you have two numbers separated by a dash, it means your zoom lens has a variable maximum aperture. It will look something like this ‘f/4-5.6’.

What Other Markings Can You Find on Your Lens?

  • ∞ – 0.5 m – Sometimes, you may find an infinity symbol, then a dash, and then a distance indicator. This is the focusing range of the lens. This indicates the closest focusing distance of the lens.
  • IS (Canon) / VR (Nikon) / OSS (Sony) – These stand for Image Stabilisation, Vibration Reduction, and Optical SteadyShot. This means that your lens has a built-in floating lens element, along with motors and electronics. These lenses sense and counteract any movement or shake.
  • Ø – The ø symbol on a lens is usually followed by a number. This is the diameter of the front of the lens. It also marks the filter size you can use on the lens. It’s necessary to know this number when purchasing screw-in filters.
  • Asph / ASP – This stands for Aspherical. It shows that the lens has non-circular lenses inside. These lens elements can be used to reduce spherical aberrations.
  • Macro / CRC (Close Range Correction) – This marking means the lens is specifically designed to be sharp at close range.
  • USM/HSM/SWM – Ultrasonic Motor, High-Speed Motor, and Silent Wave Motor are ultrasonic vibration motors that allow you to autofocus faster. The ones used in higher-end products are much quieter than those in cheaper lenses.
  • DX (Nikon) / EF-S (Canon) / E (Sony) – These lenses were explicitly created for camera bodies that are smaller than full-frame. APS-C size sensors have a crop factor. These lenses give you a focal length, taking the smaller sensor into account. These are smaller and lighter than their siblings but cannot be used on full-frame cameras.
  • Other – Lens manufacturers use a slew of markings on their lenses. Canon likes to mark their professional lenses with a red ‘L’, and Sigma uses EX for their professional and exclusive lenses.

an image of the side of a telephoto lens

What Is Lens Focusing?

Lenses have a point where the light rays going through them converge. It is called the focal point.

Focusing happens within the lens. This happens by moving one or more lens elements closer to or farther away from your camera’s imaging sensor.

The lens ‘bends’ the light and forces it to converge at different distances from the sensor.

The ideal convergence needs to fall exactly on your sensor. When you achieve that, you have a perfectly focused image or subject.

an infographic explaining lens focusing

How Does Autofocus Work?

Autofocusing is just one way to gain a sharp focus. With this mode, the camera signals the lens, forcing it to change its focal placement. How much of your scene is in focus falls on three different things—aperture setting, the distance between you and the elements in the scene, and their spatial relationship.

Many modern cameras have tons of focus points spread over your viewfinder. They can be moved or even work in groups to select a more progressive focus blanket.

Nowadays, you can choose between in-camera focus modes, which affect the alignment of the focus points and the speed of focusing. an infographic explaining autofocus

How Does Manual Focus Work?

Apart from leaving the focusing to the camera, there is the manual focus option.

Refocusing is a waste of time when capturing a subject on the same focal plane and not moving closer or farther away. Your camera might also have trouble autofocusing in other situations, like very low contrast or low light scenes. Shooting through glass is an excellent example of autofocus issues. In these times you are going to need to set the focus manually.

Older cameras had a focusing screen that helped the manual focus. Modern cameras place a red halo around objects when they are in focus. This is called focus peaking. In mirrorless systems, you can do it in the electronic viewfinder too.

DSLRs let you focus in live view mode, which means you can zoom into the picture on the LCD screen.

How to Use Autofocus with Manual?

Many lenses have a special feature, allowing you to autofocus the camera, then modify the result manually.

Some lenses will not let you manually adjust the focus when in autofocus mode. Read the user manual to see if your lens is capable of that. You can break the focus ring if you force it.

A portrait of a female model in glasses with a blurry bokeh background

What are Internal and External Focusing?

There are two different types of focusing—internal and external. You will know if you have external focusing since the lens’s front element will extend when you focus.

This is handy to know for filters, especially polarising filters. If your lens turns when focusing, you will need to focus before setting your filters to their desired effect.

What Are Distance Indicators?

Lenses, especially analogues, have built-in distance indicators. These are to focus, especially when you need to focus to infinity. They are not exactly precise. But they are a good guide for knowing which way to turn the lens to focus at a particular distance.

What Are Depth of Field Indicators?

The lenses that have distance indicators usually have depth of field indicators too. These are marked as ’22’, ’11’ and ‘8’. These numbers may differ depending on the lens, its design, and its properties.

What these markings designate is how much of your scene will be in focus at a particular aperture. These are always in relation to the distance indicators and the aperture ring. So always check these together.

a closeup image of depth of field indicators

What Are Lens Mounts?

Your lens connects to your camera body via lens mounts. There are three main types of mounts—screw (in analogue cameras), in medium format analogues they use a lock ring, and the third is bayonet fitting.

The first two is very rarely used these days, yet you may encounter them on vintage lenses.

The benefits of bayonet fittings allow lenses to be changed faster. They secure on the camera body in a much safer way. Bayonet fittings also allow electronic connections between the camera and the lens. This is what allows autofocusing and electronic control of the aperture.

Each camera manufacturer has their own lens mounts. This is except for the Four-Thirds mount, which is backed and used by several manufacturers. It is also possible to buy adapters so that lenses from one manufacturer can be used on other manufacturer’s camera bodies.

A camera lens in the foreground of a blurry dslr camera body

What is Image Stabilisation?

Many modern camera lenses have built-in image stabilisation. This feature allows you to capture scenes handheld that was previously challenging. This technology utilizes the latest gyroscopic sensors and motors to stabilise any movement in the lens elements.

Telephoto lenses are the ones that feature image stabilisation. This is because longer focal lengths suffer worse from camera shake than from shaky hands. Your images might be blurred.

The rule is to shoot at a shutter speed no lower than your focal length. A 50mm lens has a limit of 1/60th of a second, and a 300mm lens has a 1/250-1/300 range. IS allows you to bring this setting down to something more friendly.

Some cameras have built-in image stabilisation. This turns every one of your lenses into a stabilised eye.

Not all vibrations are reduced by image stabilisation. There is a limit to how far this floating lens element can move.

On top of this, camera movements that you would like to keep might be removed. For example, panning shots would not work so well.

Image stabilisation is quite power-hungry. Your batteries might not last as long as they would normally. Turn it off when not using it.

a closeup image of a camera lens stabilizer

What Filters Are Good for?

Most lenses have a filter thread in the front bezel. The filters cover a range of different options, including adding tints or darkening a scene.

Filter Threads

Every threaded filter has a different size, so it is crucial to choose the right one. On the filter, you will see the threading size that will look something like Ø=68mm. The significant benefit here is you can use these filters as lens protection.

Many photographers add a skylight or UV filter at the front. This stops any scratches, paint, dirt, or bumps affecting the front lens element.

Circular polarising lens (CPL) and Neutral Density (ND) filters are the other two most commonly used filters.

Drop-in Filters

Drop-in filters or square filters fit into a holder—the holder screws into the lens bezel.

The benefit here is that each filter you use does not have to be screwed into the lens. This is a cheaper option but less versatile than filter threads.

Rear Filters

Some lenses do not accept filters at the front of the lens. This is especially true for specialty lenses, such as extreme wide-angle/fisheye lenses.

The front of these lenses is rounded, which leaves no space for a traditional front filter. Some of these lenses have a slot at the rear of the lens where a filter can be added.

an image of a hand folding a camera lens filter

Lens Hoods

When direct sunlight hits your lens, it creates ‘flares‘ or ‘hot spots’. The sun could be hitting at an angle because you photograph the sun straight on. The lens hood stops the direct ambient light from ruining your images.

Something like this is tough to control when using a wide-angle lens with an 84° field of view. Some ultra-wide lenses have the lens hood already built-in.

an image of a camera lens with hood

Teleconverters

Teleconverters modify the behaviour of the lens you are using.

These secondary lenses sit between a camera body and a lens. They have an optical element within them, which refocuses the light.

By refocusing the light, they effectively extend the range of your focal length.

The most common teleconverters are 1.4x and 2x. A 1.4x teleconverter on your 70-200mm lens would give you an effective focal length of 98-280mm.

The downside is you lose some light as the aperture minimum also increases at the same ratio. The f/2.8 becomes f/4 and f/5.6, respectively. This results in quality loss too.

1.4x and 2x. A 1.4x teleconverter for a Canon 70-200 mm f/2.8L lens

How Can You Focus on Close Subjects?

Every lens has a minimum focus distance. This means that you can only place your lens at a certain distance to your subject before you can no longer focus.

Using macro lenses are just one way you can get closer to your subject. There are three other ways you can capture small objects at a ratio of 1:1 and closer.

How to Use Macro Filters

A close-up lens (also known as a close-up filter or macro-filter) is a way you can get close to your subjects. This secondary lens enables you to capture macro shots without the need for a special lens.

Close-up lenses work the same way as reading glasses. They allow the lens to focus more closely than it would normally. These are easy to use. Just screw on the thread at the front of the lens, and away you go.

The benefit here is that you can stack them and use multiple filters together. A +1, +2, and +4 will give you +7 steps of closeness.

How to Use Extension Tubes

Macro extension tubes are lens spacers. They do not have optical elements inside them like the teleconverters do, which is a cheap option.

They usually come in three different sizes, 7mm, 14mm, and 28mm. You can stack them together. 7mm + 14mm + 28mm = 49mm extension spacer.

Extension tubes work by reducing the focusing range of the lens you are using. You can bring your subjects much closer to your camera. However, you lose the possibility of focusing to infinity.

How to Reverse Your Lens

The other cost-effective option is to reverse a lens you already own. This might be strange, but it works well. Take the lens off and turn it around, so the front lens element is facing the inside of your camera. Now, you will be able to focus on items very closely.

There are lens reversing rings, allowing you to connect your camera mount to your reversed lens.

an image showing close focus by reversing camera lens

What You Need to Know about Aberrations & Distortions

Aberrations

When light travels through a lens, it hits and bends when encountering the glass inside. Not all light bends the same way. Some colours are affected more than others. They could be down to minor imperfections, diffractions, or refractions of the light.

Aberrations fit into two concepts. Those that work with colour (chromatic aberrations) and with single points of light (monochromatic aberrations).

Also, vignetting means that the brightness and saturation of an image decrease towards the edges of the image.

an infographic explaining spherical aberration in a camera lens guide

Distortions

Every lens has a varying degree of distortion. Generally, you will find smaller amounts when using prime lenses. This is down to fewer elements needed for the lens to work.

Constantly improving technology helps to keep distortions to a minimum. Tilt-shift lenses are also great solutions to these problems.

There are two main types of distortions. Barrel distortion makes the centre of the image appear closer than the edges. Pincushion distortion makes the centre appear much further away than the edges do.

Wide-angle lenses are plagues with distortion. Their wide field of view needs to fit on a small, rectangle surface. You will notice the centre seems unaffected. But, expect straight lines to curve as you extend to the edges of the frame.

And if you have a mixture of the two aforementioned, you will end up with moustache distortion.

an image of a mountain and sky showing moustache distortion

What Can Affect Sharpness?

Sharpness is crucial when you want to have quality photographs. This is why it’s important to know what and how can affect it.

Centre Vs. Edges

The sharpness of your images comes down to how good your lens is. Also, for optimal sharpness, you need to use your lens correctly.

Lenses tend to be sharper in the centre. The edges and corners are furthest away from the sensor and can suffer some loss. The greater edge sharpness often appears in more expensive lenses.

Zoom Range

One of the biggest problems with variable focal length or zoom lenses is their sharpness range. A zoom lens has to compromise between many features, so versatility pushes the sharpness from the top spot.

It is not always clear where the optimal sharpness lies. Some lenses are sharpest at the extremes of their range. Other lenses can be sharper around the centre of the range. There are a few lenses whose sharpest areas come and go throughout the focal length range. To find out if your lens does this or not, you need to get used to reading MTF curves.

Aperture Range

The other big thing you need to understand is that a lens curve of sharpness changes with its aperture range. Shooting wide open, your area of focus is smaller.

Go down a few stops, and you will notice a huge difference. After the peak, your lens becomes less and less sharp, but it’s a gradual change.

We have to mention lens diffraction here as well. A smaller aperture can cause it, resulting in loss of sharpness when light waves meet a barrier on their way, their behaviour changes. This happens when they hit a small hole. The aperture breaks their way.

a portrait of a young woman holding a camera to her eye

Special Lenses

Apart from zooms or prime lenses, even stepping out of the wide-angle, standard, or telephoto lens realm, there are other lenses we need to talk about.

These specialty lenses have been created for specific reasons.

What is a Tilt-Shift Lens?

A tilt-shift lens is a lens created to mimic the possibilities a large format camera gave us.

Perspective distortion is created because a large building is at increasingly different distances away from your camera. The top is farther away from you than the bottom is. A parallax error is created.

These lenses let you change the focal plane to match the relative distance of the building from the camera. This change from a perpendicular focal plane to a parallel one fixes the problem.

a graphic photo explaining shifted perspective

What is a Fisheye Lens?

Fisheye lenses are ultra-wide-angle lenses. They fall into the focal length category of anything below and including 14mm. These lenses create a very unusual perspective in photography, usually resulting in a circular image.

When we use lenses that cause barrel distortion, we correct them to create a more realistic image. We embrace the distortion and use them to create something creative. You can use them, for example, for sports, parties, or real estate photography.

a top down photo of a peninsula with a fisheye lens

What to Know About Macro Lenses

Macro lenses are specific glassware that allows you to capture small subjects and blow them up to bigger-than-life size.

Macro lenses are telephoto lenses that have a close near point. The near point is the closest point to the lens where the subject is in focus. This is why they can focus from 1cm to infinity.

These lenses have their price, but luckily you cannot only use them for shooting macro images. They function as standard lenses.

a macro image of a strawberry

Conclusion

Camera lenses are essential parts of your gear. They might be some of the most expensive too. It’s worth knowing what kind of lenses you need and what features to pay attention to.

Sometimes you can use filters or converters to save money and make your lens more versatile. Learning a few tricks from our camera lens guide will pay off.

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