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Understanding Camera Lenses: A Beginner’s Guide

Lenses. They’re arguably the most important piece of equipment a photographer can buy – even more important than the camera itself. But what makes lenses so useful? Why are some camera lenses so much better than others? The answer goes beyond simple things like sharpness and image quality. Instead, lenses matter because they control which photos you can even take in the first place.

1. The Anatomy of a Lens

Modern lenses look something like this:

Lens Diagram

Each part of the lens serves an important purpose:

  1. Filter thread: Lets you attach lens filters to modify light that reaches your camera sensor
  2. Front element: Collects light and bends it to the other lens elements
  3. Lens hood thread: Lets you attach lens hoods to block sunlight and reduce flare
  4. Zoom ring: Rotates to zoom the lens in and out
  5. Focus ring: Rotates to focus manually; does not rotate when camera autofocuses
  6. Lens name: Identifies lens
  7. A/M switch: Switches between autofocus and manual focus

Not every lens has all seven of these features, and other lenses have many more than this. However, the lens above is fairly representative of modern zoom lenses.

2. Camera Lens Terminology

Most lenses today are named in a relatively standard way:

  • Brand name, lens type, focal length (in mm), maximum aperture, other lens features/abbreviations.

The most important terms are focal length and maximum aperture. In other words, the “mm” and the “f/number” terms. These numbers are the most directly related to the types of photos you will be able to capture with the lens. (I’ve got a full section later on each one and why it is so important.)

What about the abbreviations at the end of the lens name? They still matter, denoting the extra features offered by each lens. For example, the “VR” term in the Nikon lens stands for “vibration reduction,” which stabilizes the lens for handheld shooting. However, these other terms are usually secondary in importance. Some don’t even refer to a specific feature, but instead are solely for advertising value (such as “L” on the Canon lens, which simply means it is one of Canon’s high-end lenses).

Handheld vibration reduction
NIKON D800E + 70-200mm f/4 @ 200mm, ISO 100, 1/40, f/16.0
Thanks to this telephoto lens’s vibration reduction feature, I was able to handhold it at 1/40 second and still capture a sharp photo.

The main exception to the “mm and f-number matter most” rule is when you’re dealing with specialty lenses. With fisheyes, macro lenses, tilt-shifts, and so on, your main reason for buying the lens has more to do with its unique feature than anything else.

So, what do all the abbreviations at the end of a lens name stand for? Each company labels its lenses in a different way, with potentially dozens of abbreviations per manufacturer – too many to fit in this article. However, we’ve covered all the various terms for many lens manufacturers the following guides:

3. What Is Focal Length?

The most important specification for most lenses is their focal length – in generic terms, how far “zoomed in” the lens is. Focal length is written in millimeters.

Some lenses only have a single focal length. These are known as prime lenses. A popular example is the 50mm lens – a very common first prime lens for photographers, thanks to its high usefulness and low price.

Also see our article primes vs zooms.

A few specialty lenses on the market fit somewhere between primes and zooms, such as the Leica 16-18-21mm f/4 lens. This lens covers three specific focal lengths – 16mm, 18mm, and 21mm – but none of the focal lengths in between. This is contrary to a normal zoom lens, which smoothly zooms from its widest to longest focal length.

The technical definition of focal length is a bit messy, and beyond the scope of this article. Elizabeth wrote a comprehensive guide to focal length that explains everything at a technical level.

We also have full articles introducing wide angle lenses and telephotos.

3.1. The Impact of Camera Sensor

I’ll note quickly that the sensor size of your camera contributes to the apparent focal length you’re using. This is because small camera sensors are like crops from a large camera sensor. Put the same lens on both, and the lens will appear more zoomed in on the small sensor.

Cameras with a larger crop factor (i.e. smaller sensor) will exhibit this effect the most. You can calculate the exact amount simply by multiplying your lens focal length by your crop factor. So, an 18-55mm lens used on a Nikon DX sensor – which has a 1.55x crop factor – is equivalent to a 28-85mm lens on a larger full frame camera sensor.

Here’s a general guide:

  • Wider than 35mm (equivalent): Wide angle lens
  • 35-70mm (equivalent): Normal lens
  • Longer than 70mm (equivalent): Telephoto

Anything wider than 18mm and longer than 300mm is generally considered an ultra-wide or a super-telephoto. (On Nikon DX and other APS-C cameras, that would be wider than 12mm and longer than 200mm.)

All of these are rough figures, though. Some photographers may consider 35mm to be wide angle rather than normal, or vice versa, and it’s not a big deal either way.

Big Sure Wide Angle Ocean Landscape
NIKON D7000 + 17-55mm f/2.8 @ 17mm, ISO 160, 30 seconds, f/8.0
Taken at 17mm. Since I used a DX camera (the Nikon D7000), this is only a moderate wide angle. On full frame, 17mm would be ultra-wide.

4. What Is Maximum Aperture?

The other critical term in a lens name is the “f/number” term, which stands for the lens’s maximum aperture.

First, if you are unfamiliar with the concept of aperture, I recommend reading our beginner’s guide to aperture. In short, aperture describes the “pupil” of your lens. Just like the pupil in our eyes, the aperture in a lens will let in more or less light. It is quite an important specification.

Many photographers don’t realize that aperture is written as a fraction. This is why f/2 is larger than f/4 – it’s just like 1/2 being larger than 1/4. Expensive lenses often have large apertures to let in a lot of light (again, like a large pupil). For that reason, a 24-70mm f/2.8 zoom is going to be more expensive than a 24-70mm f/4 zoom in practically every case.

Of course, even though a lens name will include its maximum aperture, you aren’t restricted to using that aperture alone. You can always change the aperture to be smaller if you want. Almost all lenses go down to at least f/16, while many allow f/22, f/32, and beyond. This is called minimum aperture.

Minimum aperture isn’t nearly as important as maximum aperture, though. It’s why you only see maximum aperture in the lens name. If you use extremely small apertures, especially f/22 and beyond, you start to add blur throughout your photos and darken them more than you’d normally want.

As with focal length, here’s a general guide to aperture:

  • Wider than f/1.4: Extremely large aperture
  • f/1.4 to f/2.8: Large aperture
  • f/4 to f/8: Normal aperture
  • f/11 to f/22: Small aperture
  • Narrower than f/22: Extremely small aperture

4.1. Depth of Field

The other reason why maximum aperture is so important is that it impacts your depth of field. Large apertures like f/1.4 and f/2.8 will give you more of a “shallow focus” effect, where the background is blurred and your subject is sharp. This is very common to see in portraiture and still life photography.

Depth of field is also influenced by the lens’s focal length. Telephoto lenses have a shallower depth of field than wide angles. So, if you really want to blur the background of your photo as much as possible, you’ll want at least a 50mm f/1.8, and probably something like an 85mm f/1.885mm f/1.4 or 105mm f/1.4. But those lenses also get progressively more and more expensive.

Tree Leaves with Noct-Nikkor
NIKON D810 + Noct-NIKKOR 58mm f/1.2 @ 58mm, ISO 64, 1/6400, f/1.2

4.2. Variable Aperture Zooms

Some zoom lenses have a different maximum aperture at their wide angle and telephoto ends. These are called “variable aperture” lenses. For example, the 18-55mm zoom I talked about earlier usually is f/3.5-5.6 variable aperture. If you shoot at 18mm, you can use an aperture as wide as f/3.5. If you shoot at 55mm, you can use an aperture as wide as f/5.6. (At focal lengths in between, your maximum aperture gradually changes from f/3.5 to f/5.6.)

In fact, these lenses can be smaller and less expensive than constant aperture zooms, making them quite reasonable in many cases. So, don’t avoid variable aperture zooms by default. Instead, look to other features of the lens, too, to see if it’s a good fit for you.

Fuji XF 100-400mm f4.5-5.6 R LM OIS WR
The Fuji XF 100-400mm f4.5-5.6 R LM OIS WR lens, a high quality variable-aperture telephoto

5. Important Lens Features

When I buy a lens, I don’t look at image quality first. Instead, there are other factors which matter more.

First: size and weight. I’m willing to give up some image quality – as well as things like zoom range and maximum aperture – to get a lighter weight lens. Of course, finding a lightweight lens can be a bit deceptive. If one heavy zoom lens replaces three moderately heavy primes in your kit, the zoom isn’t really heavy at all. Or if two lenses are equal in weight, but one goes with a lighter camera system, it’s still got the advantage.

On top of that is autofocus. Not all lenses have autofocus, and not all autofocus lenses are equally fast and accurate. It doesn’t matter as much to some genres as others, but if you’re a sports photographer, chances are good you’re willing to pay for top-notch autofocus performance.

There are tons of other lens features that matter in photography. A big one is durability/weatherproofness. If you can use your lens for several years in tricky conditions, it’s worth much more than a lens that can’t handle being bumped around.

The overall ergonomics of the lens also matter quite a bit. This includes everything from the position of the zoom ring to the smoothness of the focus ring, and how seamless it is to use the lens. You might not notice lenses with good ergonomics, but you’ll certainly notice bad ones.

6. Lens Image Quality

There are dozens of image quality factors that make some lenses better than others. I’ll go through the most important below.

First, though, keep in mind: lenses with extreme specifications are more likely to have compromises than their relatively ordinary counterparts. I’m referring to everything from superzooms to lenses with especially wide apertures. Although compromise can take many forms, it usually means lenses with lower image quality or a higher size/weight/price.

6.1. Sharpness

Right or wrong, the top feature on everyone’s mind when a new lens comes out is sharpness. The good news is that modern lenses are sharper than ever. The limit of sharpness in your photos is very likely to be your technique, not your lens.

Today, every new lens is sharp at f/8 in the center.

On top of that, most new lenses are sharp at f/8 in the corners. The same is true at their maximum aperture (whatever it may be) in the center.

The main area where modern lenses can be unsharp is at their maximum aperture in the corners of the frame. This is hardly relevant to most photographers. If you’re shooting at f/1.4, you’re likely to get a shallow focus effect. And in that case, the corners wouldn’t be sharp anyway, so your lens’s corner sharpness is irrelevant. (Milky Way photography is one exception. If you’re not a Milky Way photographer, you probably don’t need to worry about corner sharpness at f/1.4.)

6.2. Distortion

Distortion means that the lens introduces a “bulge” or “pinch” to straight lines in your images. The most obvious example is a fisheye lens, which has dramatic levels of distortion (specifically barrel distortion). If you photograph the horizon or any other flat line in your photo, a high distortion lens will show noticeably curvature or waviness.

The three main types of distortion are pincushion, barrel, and mustache. A depiction of each is below:

Pincushion Distortion Barrel Distortion Wavy Moustache Distortion

Although it’s not great to have a high-distortion lens (aside from fisheyes), this is hardly the most concerning image quality issue out there. Most photography software has built-in distortion correction that can fix the problem in one click. This can harm corner sharpness a bit, and change your composition slightly, but that’s a small price to pay.

6.2.1. Perspective Distortion

One type of distortion you’ll hear about is called perspective distortion, but it’s not the same as the distortion above. This one is not an image quality issue; it has to do with stretched-out proportions in your subject that can happen if you get too close. It’s especially visible if you use a wide angle lens, since you need to get much closer to your subjects than with a telephoto:

Red Car Perspective Distortion
NIKON D3S + 14-24mm f/2.8 @ 14mm, ISO 200, 1/125, f/8.0

This is why most portrait photographers prefer an 85mm lens rather than a 24mm lens for headshots. You can fill the frame with your subject in either case, but you need to get far closer to your subject with the 24mm. This introduces a lot of perspective distortion.

6.3. Chromatic Aberration

Chromatic Aberrations

The example above is called lateral chromatic aberration. There is also such a thing as longitudinal chromatic aberration. In that case, out-of-focus regions are the ones changing colors. Specifically, they get greener behind the subject and purpler in front of it:

Zeiss 35mm LoCA
NIKON D3S + Zeiss Distagon T* 2/35 ZF.2 @ 35mm, ISO 200, 1/200, f/2.0

It is easy to correct lateral chromatic aberration (the first one) and harder to correct longitudinal chromatic aberration. Most photography software will have some tools to help minimize it, however.

6.4. Bokeh

If you shoot shallow focus photos, bokeh will be an important concern for you. This is simply the quality of a photo’s out-of-focus blur. It was once a very specific photographer in-group term, then Apple used it in a commercial, and now it’s pretty widespread. Nevertheless, you may want to check out our full article on the subject.

Close-Up Aspen Photo from Noct-Nikkor
NIKON D810 + Noct-NIKKOR 58mm f/1.2 @ 58mm, ISO 64, 1/5000, f/1.2

Some lenses have better bokeh than others. You’ll read about it in any reviews of those lenses, no doubt. Bokeh is generally considered to be good when it has minimal texture and soft transitions, although all photographers have their own preferences.

Nikon 58mm f/1.4G Bokeh Comparison

6.5. Flare

The best lenses will have high-quality coatings that minimize flare. It doesn’t apply to every photo, but it’s a big deal when you’re working in a backlit environment. As a landscape photographer, this is definitely one of my main concerns when considering a new lens.

The sun doesn’t actually need to be in your photo in order to introduce flare. Sometimes, you can get dots of flare just by pointing the lens vaguely toward the light. Although this is a good reason to use lens hoods, it’s also a good reason to buy a lens with minimal flare.

Landscape Photo with Strong Flare
Real flare in an infrared photo. IR images often have more flare, because lens coatings focus on eliminating flare from the visible spectrum.

6.6. Sample Variation

Another component of image quality is sample variation – the idea that all copies of a particular lens fall within a similar range of image quality. It would be very frustrating to read a good review of a lens online and find that yours isn’t nearly as impressive.

Some lenses have smaller sample variation than others. This is something we try to include in our lens reviews by testing multiple copies of the same lens, but there is also plenty of luck involved. If one in ten copies of a lens is bad, most reviewers will never notice, but a high percentage of users will.

There’s no great way around sample variation, aside from testing your lenses. If you find that one or two corners are significantly less sharp than the others, that’s the best indication of a bad copy of your lens. See our articles on what to do when you get a new lens and on lens decentering.

6.7. Other Image Quality Concerns

Along with the list above, there are plenty of more specialized image quality concerns when you get a new lens: focus shiftfield curvature, starburst performance, astigmatism, and so on.

Starburst sunstar at small aperture
A high-quality starburst effect at a small aperture of f/16

7. Third Party vs Name Brand Lenses

Alongside lenses made by camera manufacturers like Nikon, Canon, Sony, and so on, countless third-party companies make lenses, too. Are these ever worthwhile choices?

On one hand, if a third-party company makes a lens that your camera company does not, it obviously is worth considering. For example, Sigma makes an 18-35mm f/1.8 zoom lens – note the wide maximum aperture of f/1.8 – for APS-C cameras. It has no equivalent from the camera manufacturers.

But many third-party lenses are similar or identical in focal length and maximum aperture to lenses from camera companies. In that case, the third party lens is usually (though not always) less expensive. Is it worth saving that money, or are you paying for third-party lenses another way – through their lack of quality?

In this case, it very strongly depends on the lenses in question. In general, third party lenses have a bit more potential for autofocus issues than name-brand lenses. They also do not always have immediate compatibility with new cameras, or camera firmware updates (although their manufacturers usually release compatibility as soon as possible).

To me, these issues are relatively minor. I generally ignore them and compare the lenses on other features instead.

For example, how good are reviews for each lens? Does either choice – name brand or third party – have poor sharpness, flare, distortion, or other issues?

You still need to do your research. There are some bad third-party lenses floating around, just like there are some bad name-brand lenses. Most – but not all – will be the companies’ older offerings.

But I’ll go ahead and say that the average, new third-party lens is no better or worse than its equivalent name-brand lens. Some are better, some are worse. You don’t have anything to fear by going this route, if it suites your budget and your photographic needs.

8. Conclusion

Hopefully this article gave you a good understanding of lenses – how they work and what to look for when you buy one. There’s a lot of information to digest, but lenses are worth learning. In many cases, they really are the most important piece of camera equipment you can buy.

If you have any questions or comments, feel free to let me know below and I will try to get back to you!

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