How do camera lenses work?
You might think that lenses aren’t very useful, perhaps just for zooming in and out. This is how I thought when I started out.
I thought that the camera body was the most important part of my setup – all I needed was the right guidance.
I had no idea that lenses did so much and that there was a heck of a lot of complicated science behind what I didn’t even think was needed.
I figured that I’d just buy a camera and start snapping away – and I’d only get a lens for added effects and zooming.
When I did my research, I was shocked that the lenses often cost more than the camera! This might come as a surprise to you too – I figured I must be missing something.
Table of Contents
Let’s Skip to the Important Part
I quickly discovered that the lens is probably the most important part of the camera and that without it, your photos will all be useless.
This started me on my journey to learning everything I could about lenses and just how important they are.
I really wanted answers to my “How do camera lenses work?” question that had been burning in my mind.
It’s a huge and technical topic – so we aren’t going to cover every aspect of it. I’ll keep it as easy to grasp as possible.
Here’s How This Guide Can Help You
Our guide will help you to correct any misunderstandings and wrongs batches of knowledge you might have. It’ll help you build a better general understanding of lenses and how they work.
By the end, you’ll have a more confident grasp of how camera lenses work – and how to best use the information to get the right lens to suit your goals and style.
Let’s get into the guide.
Camera Lenses Explained – Why are they important?
To put it basically, there a bunch of specially-shaped pieces of glass inside the lens called “lens elements”.
The number of elements varies depending on the camera lens types you’ll be using.
The job of these lens elements is to bend the light that’s coming into the lens and redirect it accurately onto the imaging sensor on the camera body.
The sensor wouldn’t be able to produce anything usable without these elements, or the lens – it’s THAT important!
What’s Do Lens Elements Do?
Lens elements work together to gather as much incoming light as possible and focus it onto the imaging sensor.
This sounds like a simple task but the science behind it is actually very difficult and complex to get right.
This is because you can’t just focus all the light onto one single place on the sensor – you want the whole image to be sharp from corner to corner.
That’s why when you’ll see some loss of sharpness at the edges of your shots when using a smartphone camera.
Technology and lens elements aren’t as good in smartphone cameras as they are in dedicated lenses.
Where are Lens Elements Found?
Lens elements are typically mounted to the inside of the lens barrel. There are also lenses that are suspended using more fancy tech and super accurate gyroscope sensors.
If this isn’t already awesome enough, these lens elements are often adjustable and movable – as is the case in zoom lenses. They weren’t really possible until relatively recently in the past, but thanks to advances in tech a physics, we now have zoom lenses.
Lenses can be carried between camera bodies – IF they’re compatible with the camera sensor.
Many photographers have carried some lenses for more than a decade.
Each time a better camera body is released; they switch over to it and get slightly better images from the same lens.
They really do supersede camera bodies and this makes it even more important to make a wise and well thought out buy when getting a lens.
The Parts of the Lens
This section is divided up into the internal parts and the external parts of the lens.
We aren’t talking about what each part does extensively, but rather giving you an idea of what everything is and where it is.
As part of this “How do camera lenses work?” guide, I suggest you get a camera lens diagram for your lens.
Take notes on it – I promise it goes a long way to help you learn everything a little faster!
The Internal Parts of a Lens
The exact layout and structure of this might vary between camera lens types and brands.
You won’t ever have to worry about opening up and fixing the inside of a lens – unless you plan on becoming a lens technician.
It’s generally too complex and difficult to deal with any of the internal elements yourself.
It helps to understand how the internal parts work together and what happens to the light once it gets into the lens.
The inside of the lens is made up of a lot of glass pieces, some are fixed and some can move.
The Internal Parts of the Lens
Here is what you’ll find inside the lens (in order from the front of the lens to the back, where it attaches to the camera):
- Front lens element
- First lens group
- Aperture opening of the lens
- Second lens group (often smaller in size than the first group)
- Rear lens element
As I said above, some of these elements are moveable and this movement helps the lens zoom in and out (for a zoom lens).
Other lens elements that aren’t fixed are used for image stabilization and counteracting the vibrations caused by your hand – all to give you a sharper image.
We’ll cover this more a bit later in the guide.
The External Parts of a Lens
Again I’ll go through these from the front of the lens to the back where it meets the camera body:
- Filter threads for attaching external filters
- Groove for mounting the lens hood
- Rotatable focusing rings
- Rotatable zoom ring (larger than the focusing rings)
- Lens notation and markings for its specifications
- Depth of field and distance marking indicators
- Aperture ring (not all lenses control the aperture this way)
- Bayonet lens mount (the old screw type isn’t made anymore – though it’s still on some old lenses)
- Controls for image stabilization and vibration reduction
It’ll be even better if you get a lens diagram for your actual lens.
Doing this along with using your lens in real life will help you learn its ins and outs faster.
The external parts are more important to you because you’ll be interacting with them far more. You won’t even have to think about your lens internal unless – god forbid – you drop your lens.
The appearance and order of the parts on the outside of your lens will vary a lot depending on the type and brand of your lens – so don’t be too set on learning this exactly as it is.
What is the focal length?
How do camera lenses work in relation to focal length?
Unless you’re inclined towards or have a keen sense for physics and technical terminology, don’t try to look up the definition of focal length.
I’ll keep it as relevant to photography as possible here. Practicality beats theory when learning these things.
When light moves through a lens, it gets turned upside down (which is why cameras have a bulky part at the top – there’s a pentaprism inside it that uses neat physics to flip the light back over again).
This flipping over means there is a point where the light converges and crosses over – leading to the flip.
This cross over point is called the nodal point.
The distance from this nodal point to the sensor of the camera is called the focal length.
Why is Focal Length Important?
Moving this nodal point closer (a shorter focal length) to the camera sensor will make the image look smaller in the photograph.
This is because there is less space between the nodal point and the sensor for the light to diverge into a larger image.
On the other hand, though, moving the nodal point away (a longer focal length) from the sensor will make the subject seem like it’s bigger in the context of the image.
Basically, adjusting the focal length changed your angle of view and zoom factor.
How to Read Focal Lengths
Focal lengths are expressed in millimeters and this is how to read them:
- Longer focal lengths are represented by higher numbers (in mm) – they are more zoomed in and have a narrower angle of view
- Shorter focal lengths are represented by lower numbers – they are more zoomed out and have a wider angle of view
The focal length is one of the main ways that lenses are differentiated and is probably the most influential factor in deciding which lens will work best for each type of photography.
Long focal lengths give you a “telephoto lens” and short focal lengths give you a “wide-angle lens”.
We’ll talk more about this in a bit.
What to Know About Prime and Zoom Lenses
We’ve already spoken about this a little earlier so we won’t get too much into it again.
Just bear in mind that each option comes with its strong and weak points – and this needs to be balanced against the cost and versatility of each type.
Zoom lenses use fancy engineering, physics, and design to let the lens move the internal elements around to adjust and change the focal length of the lens – without having to change the lens.
The benefits of this are obvious as you could shoot something up close and then zoom in to shoot a far-away subject in a matter of seconds.
All this is done without having to change lenses or physically walk closer to your subject.
Zoom lenses change the configuration of the little lens elements to achieve this – it’s a marvelous discovery and has led to zoom lenses being used so widely today.
There are some trade-offs made to give you all the extra versatility of a zoom lens.
If the trade-offs aren’t worth it to you, then prime lenses might do it for you!
Prime lenses are the inverse of zoom lenses and don’t have the ability to change their focal lengths.
Prime lenses are generally cheaper and take sharper images than zoom lenses (since there are fewer moving parts inside).
Does Aperture Matter?
How do camera lenses work with different apertures? We’ll answer this question below.
Aperture is just a fancy word that means “opening” – the opening that allows light into the lens.
Without this aperture, you’d have no control over the amount of light that’s let into lens.
Aperture is measured and written as a fraction of the focal length of your lens. This will tell you the size of your aperture in millimeters.
Understanding Aperture Stops
Aperture sizes are in order of f-stops. Each f-stop lets in double the light of the previous stop.
Here’s an example to help you understand better:
Let’s say your focal length is 50mm, and your aperture is set at f/2.0.
50/2 = 25mm. This means that the actual size of the opening of the aperture is 25mm.
If you decide to shoot at f/4.0, your aperture opening size will become 50/4 = 12.5mm.
From this example you can see that:
- lower aperture numbers (f/2.0) lead to wider aperture openings = more light let into your lens
- higher aperture numbers (f/4.0) give you a narrower opening = less light is let into your lens
Maximum Aperture is What You Should Look At
The maximum aperture refers to the widest that the aperture of your lens is able to open.
If your aperture can open wider, your lens will perform better in low light and can be faster than lenses with a narrower aperture.
Although there are a lot of lenses that have a variable aperture, the maximum aperture should be what you primarily base your decision on.
When it comes to lenses, brighter is better – and you get a versatile and capable lens.
Keep in mind that lenses with a wider maximum aperture are more expensive and can dig a deep hole into your budget – but it’s worth the investment.
Is Variable Aperture Good or Bad?
I’ve come across this question hundreds of times before.
One important thing to consider when buying a lens is that you’ll never find the perfect lens that can do everything better than all other options.
There is always a give and take where you make certain sacrifices to get closer to your goals – this is certainly true here too.
There are a lot of pro photographers who won’t use a variable aperture lens – as it makes sacrifices where they aren’t willing to give up.
Variable apertures are often written as two apertures linked by a hyphen (f/3.5 –f/5.6).
These lenses are lighter, smaller and a lot cheaper than fixed aperture lenses – but you’ll get slightly less sharp images as the trade-off.
What is Focusing and How Does It Work?
Remember we spoke about how rays of light need to converge first in order to cross over and be flipped upside down?
This cross over point needs to be focused onto as few pixels of the imaging sensor as possible.
The better this is done, the sharper your images will turn out.
Focusing is achieved by moving the lens elements closer to or further away from the sensor – it’s all done inside the lens and it’s pretty technical so we won’t go deeper on it.
All you need to know is that in order to get perfect focus; you need the crossing point to all be on the sensor.
This is controlled by the camera and it works like this:
- autofocus starts and begins to focus closer toward infinity
- if the image begins to get sharper, it continues to focus towards infinity
- if the image doesn’t get sharper, then it focuses nearer and nearer until it does
- it will continue to focus closer to infinity until the image starts becoming less sharp
- at this point, it will pull back again until the image starts losing sharpness
- as soon as this happens, autofocus will return to the best focus point
Autofocus is fast and accurate in most modern lenses and camera bodies.
You can rely on autofocus to take care of you in most situations, though you may struggle in low light and low contrast conditions.
Manual focus is usually better when you know the focus area isn’t going to change or you’re waiting for a moving subject to passing through your preset focus area.
Other than these, you’re probably better off using autofocus – using manual focus well will take time to build up your eye for it, and muscle memory.
Our Final Thoughts
You should be able to answer the “How do camera lenses work?” question with confidence now.
You know what’s inside a lens, what its most important features are, and what happens to light as it passes through.
Of course, there’s more to learn so take it in slowly.
It’s a complicated topic that shouldn’t be rushed – take on new information as you get more familiar with your lens and how it works.
Be sure to experiment with your lens and try to do some new things with it. Experience is a great teacher and one of the best ways to put theory into practice.
As you practice and improve, make sure you practice proper cleaning and maintaining of your lenses.
They are a significant investment, so it’s important to get a long life out of them. If you treat them well, they can last you several years and travel with you as you upgrade your camera bodies.
The next time somebody asks you, “How do camera lenses work?” You’ll be able to give them a pretty solid answer. As you get back out there, remember to keep improving – and have fun doing it!