Camera Lenses Explained - My Beginner's Guide

A listener asked me to do an episode strictly on lenses, so here it is. If you want me to explain something, just hit the “Send us a text” link on the podcast feed, and you can have your own almost personalised episode of the podcast. How utterly splendid.

Lenses attach to cameras and focus what you point your camera at onto the camera sensor. So, lenses are quite important in photography terms!

In this episode, I tell you.

• What are the main types of lenses?
• What focal length is (quickly).
• What aperture is (not as quickly).
• What does this stuff all mean to you?

I also want to tell you

• What if you use a phone to take photos?
• What I do.

All explained in plain English, without the irrelevant detail, in less than 27 (ish) minutes!

What is not to love? How utterly splendid.

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• 13:47 (Cont.) Camera Lenses Explained - My Beginner's Guide

Transcript

Hi, and a very warm welcome to Episode 189 of the Photography Explained podcast. I'm your host, Rick, and in each episode, I will try to explain one photographic thing to you in plain English in less than 27 minutes (ish) without the irrelevant details. I'm a professionally qualified photographer based in England with a lifetime of photographic experience, which I share with you in my podcast.

Here is the answery bit
Camera lenses attach to the front of camera bodies and focus what you are taking a photo of onto the camera sensor. You can get lenses with different focal lengths, maximum and minimum apertures, and varying sizes, weights, and quality. I will explain all these in this episode and tell you what lenses I use.

Oh yes - you can get cameras with the lens physically attached to the camera - I am not talking about those. Although most of what I talk about here applies. 

This is a listener question from Karyn in Gloucester, Virginia. Karyn texted me this.

"Hello, Rick! I am a hobby photographer and learning quite a lot from your podcast, thank you for that! Can you do an episode strictly on lenses, explain in detail what the numbers mean, what is best used for what situation, etc? It can be quite confusing for a rookie! Thank you, Karyn P.S. if you are already done an episode like this, would you mind sharing the number? I haven't been able to find one. Cheers!"

I have done some episodes on lenses before, but I decided to do a new episode.

Thanks very much for getting in touch Karyn, and I am delighted to finally answer your question. You can text the show by hitting the "Send us a text" thing on the top of the episode notes. Thanks again for getting in touch, Karyn; now let me crack on with answering your question.

That was the answery bit - here is the talky bit.
First off - why not have a built-in lens?
Well, you can get cameras with built-in lenses. These days, they tend to be called phones, though! Just saying. Cameras that can take different lenses give more options. It is that simple. You choose the lens or lenses that work for you.

Interchangeable lens cameras have the acronym ILC, although I have never used this acronym other than to tell you what it means. So, let's forget that and move on. I am talking here about mirrorless cameras and DSLR cameras, okay?

What does the lens on a camera do?
In very simplistic terms, the lens focuses the light onto the camera image sensor. Oh yes, it also allows you to see what you are taking a photo of.

On a DSLR camera, you are actually looking through the lens when you are composing and taking a photo. On a mirrorless camera, you are not, as there is no mirror - well, you wouldn't expect one, would you with that name! No, with a mirrorless camera, you are looking through an electronic viewfinder, which shows an electronic interpretation of what your lens is capturing.

What about those numbers on lenses?
There are numbers on lenses, such as focal length and aperture. So, Karyn, let's start with these, as you asked specifically about them.

What does focal length mean?
Well, the focal length of a lens determines the angle of view. Focal length is the distance from the focal plane to the nodal point in the lens.

Simple eh?

The focal plane is the camera sensor. Or in a film camera, the camera film. OK, that makes sense.

The nodal point is a point somewhere within the lens. If you had a lens with a single lens element, that would be the nodal point. Lenses have more than one element though, and the nodal point is in there somewhere. I have read the words describing this but don't understand them. And understanding this won't help me. This is what I call irrelevant detail.

But to make sense of this, a 50mm lens on a full frame camera gives a field of view similar to that which we see with our own eyes.

A lens with a focal length of less than 50mm gives us a wider field of view. This is a wide angle lens.

A lens with a focal length greater than 50mm gives us a narrower field of view. This is called a telephoto lens.

I will come back to this. But the other part of a lens is the aperture,

What is the aperture in a lens?
The aperture is a bladed type device within the lens that changes the size of the lens opening. If a lens has a maximum aperture of f/4, and you use f/4, the aperture is actually invisible. If you choose a smaller aperture, such as f/8, the aperture thing appears and reduces the size of the lens opening.

This reduces the amount of light that gets through to the camera sensor (or film). The number on the lens is the maximum aperture, which, unhelpfully, is the smallest number. Change to the highest aperture number, and this is called the minimum aperture. Which equally unhelpfully is the largest number.

It has to do with maths and reciprocals, things that I have no chance of understanding.

• The larger the aperture, the more light gets through to the sensor.
• The smaller the aperture, the less light gets through to the camera sensor.

With my Canon 17-40mm f/4 L lens, the maximum aperture is f/4. The minimum aperture is f/22.

What do these aperture values mean?
What does the number f/4 actually mean? No idea. No idea at all. But f/4 to f/5.6 is one stop. As is f/5.6 to f/8, f/8 to f/11, f/11 to f16, f/16 to f/22. Each stop is a halving or a doubling of light, depending on which way you go. And this comes into play when getting the correct exposure.

f/4 to f/22 is the aperture range of my Canon 17-40mm lens.

But I can't tell you what f/4 is, what it actually means

Check out episode 171, where I come up with a new aperture scale, which makes just as much sense as the one that we have.

The larger the lens's maximum aperture, the bigger, heavier, bulkier and more expensive a lens is. Lenses with a wider maximum aperture let more light in, but there is a price to pay. So, be careful when choosing the right lens. 

No. Let's not worry about what the numbers actually are, just what they do. The smallest number is the biggest aperture, and the largest number is the smallest aperture. I mean, really, it could have been the other way around, right?

And the highest image quality will be an aperture somewhere in the middle. On my Canon 17-40mm lens, it is f/8.

Depth of field explained quickly.
The depth of field changes with the aperture. 

Depth of field would be better called depth of sharpness; it is the amount of a photo that is sharp from front to back.

• The larger the aperture, the less depth of field.
• The smaller the aperture, the more depth of field.

The focal length also changes the depth of field. 

• The larger the focal length, the less depth of field.
• The smaller the focal length, the more depth of field.

A larger aperture gives a shallow depth of field; a smaller aperture gives a deeper depth of field.

That is depth of field done. Oh no, sorry, where you focus and where things are in a composition also affect depth of field. I will add depth of field to my list of episodes.

What are the main types of lenses?
Standard lenses, wide angle lenses, telephoto lenses, macro lenses, fisheye lenses, and tilt-shift lenses.

Standard lenses have a focal length of around 50mm on a full-frame camera. I say a full-frame camera. That is a camera with a sensor which is 36mm wide x 24mm high. I need to talk about crop factors here. Sorry, but I have to do this.

What is the crop factor?
A full frame camera has a notional crop factor of 1. So a 50mm focal length is a 50mm focal length, with a horizontal field of view of around 40 degrees.

A cropped sensor camera has a crop factor of 1.5-1.6, depending on the camera, meaning that a 50mm focal length on a cropped sensor camera has an effective focal length of 50x 1.5/ 1.6, which is 75 or 80mm, giving a horizontal field of view of around 25 degrees.

To get back to 50mm, you need to divide the focal length by the crop factor, so 50/ 1.5 or 1.6 + 33-31mm.

A micro four thirds camera has a crop factor of 2, meaning that a 50mm focal length on a cropped sensor camera has an effective focal length of 50x 2, which is 100mm, with a horizontal field of view of around 209 degrees.

So, to get a 50mm focal length, you need a 25mm focal length.

Simple eh!

Unfortunately, this is a fundamental point that applies to all camera lenses.

Full frame cameras, we are fine. The numbers are the numbers. However, with cropped sensor cameras and micro-four-thirds cameras, you have to multiply the focal length by the crop factor to get the effective focal length.

Now that I have dropped that bombshell, I will explain the main types of lenses.

Back to standard lenses
A 50mm focal length on a full frame camera gives a 50mm focal length. This is similar to how we view the world with the human eye.

A 50mm focal length on a cropped sensor camera is 75-80mm focal length. But to get the same field of view as with a full frame camera you need to use a focal length of 31-33mm.

And with a micro four thirds camera a 50mm focal length gives an effective focal length of 100mm. And to get the same field of view as with a full-frame camera, you need a 25mm focal length.

I'm going to explain everything from hereon for a full frame camera to you. To keep my sanity. And yours.

So 50mm is a similar view to how we see the world. That is the kind of focal length that you use to give a perspective that looks natural and familiar, how we see things day to day.

There is no defined divide between wide angle, standard and full frame lenses. So, a standard lens could be between 40 and 60mm. Some will say less than 50mm is wide angle, and more than 50mm is telephoto, but it isn't quite like that.

What is a wide-angle lens?
Wide angle lenses have a focal length of less than 40mm ish. A wide angle lens gives a wider field of view than a standard lens, which is a relief. The smaller the focal length, the wider the field of view. And the smaller the focal length the smaller things look, and the more depth of field you can get.

What is a telephoto lens?
Telephoto lenses have focal lengths of more than 60mm ish. Telephoto lenses give a narrower field of view than a standard lens. The larger the number, the narrower the field of view. And the larger the focal length the closer things are, and the less depth of field you get.

What is a macro lens?
Macro lenses are used to get close to things, such as, oh, I don't know, flowers, insects, and very small things. You get super close, but there is the challenge of depth of field to contend with. But you use a macro lens to get those amazing close-up photos of all sorts of things.

And what is a fisheye lens?
Fisheye lenses are super wide and can give you an impressive 180-degree field of view. Other fields of view are available. You get loads of distortion, but these lenses can be used to great effect. I used to have a fisheye zoom lens, which I loved. Although I didn't really need it!

Tilt-shift lenses
Tilt-shift lenses are specialist lenses used to give very specific depth of field and correct things like the converging lines on buildings. Super clever lenses, but they are manual focus, which was a challenge to me with my ageing old mince pies!

Autofocus
Nearly forgot this.

Most lenses are autofocus, but you can turn this off and focus manually. The last time I focussed manually was probably in 1978. Why would you ever turn off autofocus? Now, I know someone will point out some very specific situations where you need to do this, but, in general terms, use autofocus. I do.

Prime lenses vs Zoom lenses
A prime lens has a fixed focal length.  Like a 50mm f/1.8 lens. Prime lenses are smaller, lighter, and, indeed, cheaper than zoom lenses.

A zoom lens has a range of focal lengths.

I have a Canon 24-105mm lens, which goes from wide angle, 24mm, through standard, 50mm, to telephoto, 105mm. This is a very versatile, general-purpose lens. You can also get wide angle zoom lenses and telephoto zoom lenses. These offer much more flexibility than prime lenses.

Variable focal length lenses are very popular these days - I don't have any fixed focal length lenses these days.

Kit lenses explained quickly.
Now, this is an odd term. Kit lens really means the cheaper lenses that you get with cheaper cameras. A great example is the 18-55mm lens. These are cheaper lenses with lower quality than other, more expensive lenses. These are beginner lenses if you like. 

But you can also get kits with more expensive lenses. But the term kit lens really means the 18-55mm lens and is similar in terms of cost and quality.

Lens mounts
A lens fits onto a camera body using a lens mount. Each camera system has its own specific mount. You can't put a Canon lens on a Nikon camera. Nor a Nikon lens on a Canon camera. But micro four thirds cameras all have the same mount. So there you go.

Who makes lenses for cameras?
Camera manufacturers make lenses that go on their cameras. 

However, there are third-party lens manufacturers who make lenses that fit on more than one camera. And the quality of these third-party lenses is, in many cases, as good as, if not better than, those made by the camera manufacturers.

Lens Quality
In general terms, the more money you pay, the higher the quality of the lens. The higher the quality of the lens, the higher the image quality. A massive generalisation but a good rule of thumb. But lenses last a long time. My main lenses I have had of over 10 years now, and they still work as well today as they did when I bought them. So get the best lenses that you need that you can reasonably afford.

Lenses also have optical errors within them, such as chromatic aberration and softening at the edges at maximum aperture. Find out what defects your lens has - they all have them!

And you can take a rubbish photo with the best lens in the world!

Reselling lenses
Now, buy a lens, and if you want to sell it in a few years, you might be pleasantly surprised by what you get for it. Cameras depreciate much more quickly than lenses, which makes sense if you think about it.

One last thing - fast lenses
Aaggh. I hate this term. This is a stupid photography term. A fast lens is a lens with a large maximum aperture. But is it not fast.

The talky bit
How did we ever end up with these numbers? Crop factors, focal lengths, effective focal lengths. It doesn't help us, does it? I have come up with an answer to all this nonsense. Check out episode 171, titled The Future Of Photography – Making Sense Of It In 2024.

I have described the main types of lenses in this episode, and I wanted to explain how to use them and also how to look after them. Do you know what? I will do just that in the next episode.

I used to have loads of lenses. I have had all the lenses I discussed in this episode. You need to determine which lenses are the best for you. This will be very specific to you, what you do, and, of course, what you like. 

What if I use my phone to take photos and not a camera?
Well, my iPhone 15 Pro has three lenses. They are 

• 13mm, or 0.5x
• 24mm, or 1x
• 77mm, or 3x

Now the focal length cannot possibly relate to the distance from the focal plane to the nodal point. My phone is nowhere near 77mm deep! So there is something else going on here. 

I like the magnifications that Apple has used. I have adopted this for my new world of photography, which you can find out more about in episode 171, which I mentioned not long ago.

The only thing I want to say here is that my iPhone has these different lenses, which are brilliant. But be careful using digital zoom cos things can go quickly wrong.

What do I do?
I use zoom lenses. With my Canon system, I have a Canon 17-40mm f/4L lens, which I use for my photos of buildings. I normally use the 17mm end of the focal length, which gives me a horizontal field of view of a whopping 93 degrees. Great for interiors and exteriors. I also have a Canon 24-105mm lens and a Canon 70-200mm lens.

All these lenses have a maximum aperture of f/4. That is all I need. I take my photos of buildings with my camera on a tripod, so I am not worried about camera shake or using a faster shutter speed. No, I am fine. I use ISO100 and slower shutter speeds, whatever the camera chooses.

I used to have loads more lenses, but they have all gone. These days, I stick to what I need.

And with my Olympus system, I have a 12-42mm pancake lens, which is my default lens, so small it makes the camera almost pocket-sized. I love this lens. I also have an Olympus 12-40mm f2.8 lens, with an effective focal length of 24-80mm focal length, and an Olympus 40-150mm lens, with an effective focal length of 80-300mm.

I use f/8 as this gives the best quality and depth of field that I need. That is with both camera systems.

I have a favourite lens for each camera system, which helps me to take the photos that I take. And that is it. And a new lens for me is a rare event. The last time I bought a new lens was to replace a lens that I broke.

That is what I do.

Some thoughts from the last episode
Think before you take every photo. Is what you are taking a photo of interesting? Will someone else find your photo interesting?

If the answer to either question is no, don't take the photo. Sorted. Move on, Rick.

Next episode
Do you know, I will have to do another episode on how to use lenses to take the best photos you can. I have explained all about lenses in this episode, 

Having explained camera lenses, I wanted to talk about looking after these lovely things, so I need to cover that as well. I also want to talk about how to choose lenses, so this might end up being in three episodes, which is fine. 

Ask me a question.
If you have a question you would like me to answer, email me at sales@rickmcevoyphotography.co.uk or visit the podcast website, photographyexplainedpodcast.com/start. Or text me from the podcast feed like Karyn did.

If you want to say hi, please do – I love hearing from my listeners.

OK - I am done.
This episode was brought to you by a space in my script because I didn't know what I was going to eat. But now I do know. It was a cheese and pickle sandwich with some water, but no crisps, which I consumed before I settled down in my homemade, acoustically cushioned recording emporium.

I've been Rick McEvoy. Thanks again very much for listening to my small but perfectly formed podcast (it says here) and for giving me 27 minutes of your valuable time. After I have edited out the mistakes and other bad stuff, this episode will be about 30 minutes long.

Take care and stay safe.

Cheers from me, Rick