Things To Consider Before You Buy a Lens

Things To Consider Before You Buy a Lens

There’s a lot of talk about cameras and, consequently, lenses get overlooked. With competing priorities when you buy a lens, here are some things that could affect your decision on which lens to buy.

In photography, there is always a payoff. Whatever advantage a particular choice brings, there will be a disadvantage. Also, any rule in photography should be treated as if we mean “as a rule,” and not a hard fact. There are always exceptions. So, as a rule, if we consider buying a lens we want it to help us get the best quality photo possible. So, we’ll start by thinking about what we want to avoid.

Aberrations and How to Avoid Them

Chromatic Aberrations

An aberration is a lens defect that prevents the lens from forming a perfect image. Often, this will mean that some of the light entering the lens will be focused too near or too far from the focal plane. Sometimes this may be light of a particular wavelength, so light is split, causing colored fringing most visible around high-contrast edges. That effect is called chromatic aberration.

Shot with a Nkon bridge camera back in 2004, and nowhere near the optical standards we expect today, colored fringes are clearly seen on the edges against the sky and the focus is off. Click on the image to see a larger version.

Lens Flare

Visible lens flare is an aberration where light enters the lens and bounces off internal surfaces. This is usually unwanted. However, it can be used as a creative effect. Think of JJ Abrams’ films and the horizontal lines of lens flare resulting from the anamorphic lenses used in cinema. Good quality lenses have coatings on the internal lens elements that prevent light from being reflected from their surface.

The lens flare seen here was caused by a scratch on the front element. Shortly before this shot, I had removed sea spray from the lens. Despite my care, a grain of sand scratched the glass.

There’s a second kind of lens flare where the image's contrast is reduced by the light falling on the lens' front element. This can be avoided by using a lens hood that shades the lens.

Distortion

Barrel distortion is a lens aberration that stretches the image around the edges. Thus, a square becomes barrel-shaped because magnification reduces towards the edge of the lens.

Barrel distortion to a rectangle.

The opposite, pincushion distortion, is more likely to be seen on a telephoto lens. In that case, the scene's edges are distorted inward, towards the center.

Pincushion distortion.

Vignetting

Vignetting is darkening at the corners and edges of the frame. It is caused by light at extreme angles being blocked off by the lens barrel. It can sometimes be avoided by zooming in, thus cropping the vignette, or stopping down the aperture. The smaller aperture reduces the overall amount of light and the angle at which the light enters the lens is also reduced. Thus, the light from the center of the lens is visible at the corners.

Many fast fixed focal length lenses have vignettes that rapidly disappear as the aperture size reduces. However, one must also be aware that small apertures can result in softer pictures as the light refracts (bends) around the aperture blades, scattering the light before it hits the sensor.

I couldn't find any images in my catalog with a vignette, so this was added in the image development as an illustration.

Lens Breathing

Lens breathing is an unwanted change in focal length as the focusing distance changes. Even expensive prime lenses can exhibit it, but cheaper lenses tend to exhibit it more, thus making photo stacking more difficult.

Beauty Defects

Beauty defects are visible cosmetic flaws in lenses that don’t adversely affect the image. When you buy second-hand lenses, retailers will mention that dust is visible inside the lens, but this won’t affect image quality.

So, What Are We Looking for in a Lens?

You Get What You Pay For

When buying gear, price may be an important factor for you. Nevertheless, the more you pay the better it is. Which bracket should you choose? Unless you have a blasé attitude to image quality and are just snapping away selfies for social media, get the best you can afford.

If you are paying big bucks for a lens, it had better be good. This Nikon 800mm lens costs $16,296.95.

Lenses usually fall within one of three quality brackets. The low-end hobbyists’ lenses are cheaper and don’t perform as well as the mid-range enthusiasts’ lenses. Those, in turn, are not as good as the top-quality professional lenses. What goes into producing a top-of-the-range lens is a far cry from the mass-produced kit lenses that come as standard on entry-level cameras. That doesn’t mean those cheap lenses are necessarily bad, though some are, but more expensive lenses are better.

Prime Lenses

Although it wasn’t their original definition, prime lenses are now considered to be those with a fixed focal length. Zoom lenses can vary their focal length. The quality of zoom lenses is far better now than twenty years ago and can have superb image quality. However, prime lenses in the same quality bracket will usually give better image quality, but they don’t have the versatility of a zoom.

A Sigma 16mm f/1.4 prime lens.

Optical Quality

Optical quality is usually an important consideration for photographers. Good lenses minimize distortion and aberrations and so deliver sharp, clear images. To achieve this, lenses require meticulous design and manufacturing. That is why the best lenses are often the most expensive. Top-grade lenses have aspherical elements made with higher-quality glass. That glass requires ultra-precise grinding and polishing. They will probably contain one or more extra low-dispersion elements that reduce chromatic aberrations and high-refractive index elements that help manufacturers make lenses smaller and lighter. This glass has several different proprietary names depending upon the manufacturers, but you will usually see them mentioned in the lens specifications.

Good quality lenses should be fast to focus and not exhibit lens flare, chromatic aberrations, or other defects even when shooting in challenging conditions such as contre-jour.

Counting the Number of Lens Elements

Looking at the specifications, you may notice that lenses have different numbers of elements. Fewer elements should give better light transmission. However, that doesn’t necessarily translate into better image quality. More elements can help correct aberrations. Furthermore, more complex designs, such as those found in zoom lenses, require more elements to work.

Does Length Matter?

The focal length is the distance from the lens' optical center to the sensor when the lens is focused on infinity. Without getting too hung up on the physics, the longer the lens, the narrower the field of view, and the closer objects will appear. Thus, distant objects seem more magnified with a long lens because they fill the frame. Wider-angled lenses mean a broader view appears in the picture, so subjects appear smaller.

Using a 12mm wide angle lens, distance appears exaggerated and the photo appears to have more depth. The island seems far away compare to the next image despite it being taken physically closer. In this shot is it approximately a mile from where I stood. The vignette was added in development.

The focal length changes the appearance of a scene in other ways too. A wide angle lens will make objects close to the lens seem far larger than those just a little way back. You’ve probably seen the pictures of kittens and calves where their noses seem unnaturally large. These were shot with short wide angle lenses close to the animal's face. It's cute with baby animals but not a good look on humans. Meanwhile, long telephoto lenses appear to compress the image and can flatten subjects so they look like cardboard cutouts. They make distant objects appear much closer to objects at the front of the scene.

Using a longer lens, the island is more than 1.8 miles from where I stood but appears much closer because of the 500mm focal length.

There’s no hard and fast rule here and the numbers may be different depending upon the sensor size of the camera you use. But as a generalization, a typical wide angle lens might be somewhere in the range of 7-30mm, depending upon the camera. They are great for landscapes. Telephoto lenses are often 60mm or longer, although usually in the low to mid-hundreds. They are used for photography where the subject is farther from the camera, such as sports and wildlife. In the middle are standard lenses, normally employed for portraiture.

Standing at about the same location where I took the first island picture above, this time my lens was set to 25mm.

A mistake many beginners make is buying cheap, long lenses. Big is better, right? Wrong! The longest possible lens isn’t necessarily the best solution. Unless you pay lots of money, long lenses are slower and have poorer image quality. Getting physically closer to your subject will always give you better results. Also, zoom lenses with a limited range perform better across all focal lengths than those with a smaller range. A 70-200mm lens will be better than a 70-300mm.

Does the Aperture Matter?

The size of the aperture determines how much light enters the lens. Wider apertures (i.e., lower f-numbers) allow better low-light performance, therefore faster shutter speeds at lower ISOs are possible. They also give you more latitude for controlling the depth of field.

Bokeh with balls of light reflected odd the water's surface.

The number of blades and their shape will affect the nature of the out-of-focus area, or bokeh. A smooth, creamy bokeh usually results from a high-quality lens with many rounded aperture blades. That too will create round balls of light in the bokeh, whereas six-bladed apertures will produce hexagons. What's seen as undesirable are asymmetrical light balls.

Build Quality

Construction and durability are important factors. I recommend lenses that have at least a metal bayonet mount. All-metal lenses withstand wear and tear better, ensuring longevity. They are usually more expensive than their plastic equivalents. However, plastic lenses are lighter.

Fast Focusing

Autofocus performance is important too. Fast and accurate autofocus enhances usability. Cheap bottom-end lenses are not great at tracking fast-moving subjects.

Older lenses used a screw-drive mechanism for adjusting the autofocus. Cheaper lenses replaced those with a micromotor, which uses tiny gears to drive the lens. Higher-quality models use faster piezoelectric motors. These come under a variety of names such as Supersonic Motor (SSM), Voice Coil Motor (VCM), Ultrasonic Motor (USM), Silent Wave Motor (SWM), Hyper Sonic Motor (HSM), and many more. This mechanism type is both fast and quiet. Although their design can vary, they are all based on piezoelectric materials that change shape when they receive an electric current.

To capture action like this tern emerging from the water after its dive you need your lens to focus quickly.

Weather-Sealing

Do look at splash and dustproofing. There’s no point in buying a weather-sealed camera if the lens isn’t similarly protected. However, with one exception, there is no legal definition of weather-sealing and I know people whose supposedly splashproof cameras and lenses have died after a rainfall. Ideally, you want a camera system with an ingress protection (IP) rating, but only one manufacturer offers this.

With my camera standing on a tripod in the torrential downpour, I needed to be sure of its IP53 weatherproofing.

Third-Party Lenses

There are numerous manufacturers of third-party lenses. Sigma and Tamron make some consumer-level and high-quality lenses, and the former is often subcontracted to make lenses for camera manufacturers. Generally, their equivalent lenses are cheaper than the manufacturers' own models, but may or may not have quite the same performance, so do your homework.

Other manufacturers such as 7Artisans, TT Artisans, Meyer-Optik Gorlitz, Lensbaby, Samyang, and SLR Magic produce a wide range of lenses. Some are high quality, while others are quirky and good fun.

You can also buy adapters to fit vintage lenses from film SLRs onto most cameras. These give a completely different feel to your photos.

The Lensbaby Composer Pro II

Compatibility

Ensure the lens fits your camera’s mount and sensor size. Lenses from the same brand don’t necessarily fit all the bodies from that brand, and the recent shift to mirrorless cameras from DSLRs caused much confusion for people.

Finally, decide what you need and research whether a lens meets your needs. Then, if you can, take your camera to a camera shop and try it with that lens. Take some test shots and see how it performs before you part with your cash.

If you are thinking about buying a camera for the first time, please check out my article about that.

Ivor Rackham's picture

A professional photographer, website developer, and writer, Ivor lives in the North East of England. His main work is training others in photography. He has a special interest in supporting people with their mental well-being. In 2023 he accepted becoming a brand ambassador for the OM System.

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26 Comments

Before anyone comments, yes, I've spotted the typo!

As the saying goes:
"If anybody finds a typo, he's allowed to keep it."
;-)

I didn't know that saying. Thanks. I proofread these articles multiple times, and the editors check them, yet they still slip through. Hopefully, it will be fixed before too long. Did you spot it?

English isn't my first language, so I wasn't in "typo-deteccting-mode". So, no, I didn't spot it.

PS: Although I knew most of what you've written in the article, I still learned something new.
As I don't use focus stacking, I had never thought about the implications of focus breathing on focus stacking. So, in case I try focus stacking in the future I'd look for a lens with no or minimal focus breathing first.

Thank you. I had no idea English wasn't your first language. You can't tell from your writing. The typo has been corrected now. I mist the S of Things in the title.

I didn't spot the typo, but I did register just to say, thanks for a great article.

Thanks, John. It has been fixed now. The S was missing from the word Things in the title.

Thank you.I enjoy your articles.

I did spot the typo thing.

Thank you, Tessa, That's very kind. Well spotted and well integrated into your reply, haha.

Just remember, "When you make a typo, the errorists win!"

Ha ha, very good Willy.

One to add, though it's a consequence of several factors you mention in the article, is size/weight and how that affects usability. I'm always more likely to pickup a smaller, lighter lens for personal photography, and I have larger, heavier glass that is almost exclusively used for client work.

That's very true. Thanks.

Also, as you age unfortunately, some lenses become more challenging to use. My bad shoulders really tell on me when I am using my EF100-400 L shooting waterfowl. Just a fact of life.

Do you use a monopod, Ed? I had a client who was having similar issues and I let them try an old one I have here, and they subsequently bought one.

No, right now I just shoulder on. I am one of those old school guys who keeps going until I can’t do anymore. I use my tripod for landscapes. I just don’t want to carry any additional gear.

Cool, keep at it. I am another minimalist when it comes to carrying gear too; a camera, lens, maybe a tripod for landscapes, and possibly a filter in my pocket. These days I rarely even need a spare battery.

" Think of JJ Abrams’ films and the horizontal lines of lens flare resulting from the anamorphic lenses used in cinema." What most people call flare in Abrams' films is actually coma from off-axis point-sourced light.

"The focal length is the distance from the lens' optical center to the sensor when the lens is focused on infinity" Actually, it's the distance from the lens' front nodal point to the film/sensor at whatever distance you're focused at. (Yes, the focal length changes, which also changes the f/stop ratio.) On telephoto lenses, the front nodal point is well in front of the lens.

"The number of blades and their shape will affect the nature of the out-of-focus area, or bokeh. A smooth, creamy bokeh usually results from a high-quality lens with many rounded aperture blades. That too will create round balls of light in the bokeh, whereas six-bladed apertures will produce hexagons. What's seen as undesirable are asymmetrical light balls." Bokeh is a very complex phenomenon, affected more by the design of the lens than the aperture shape. Triplets give "soap bubble bokeh", Petzvals give "swirly bokeh", etc. Shape of the aperture only affects the shape of out-of-focus specular highlights, which is more flare than bokeh.

Thanks Mark. Yes, I could have gone much more in-depth into any of these topics, but the article was already 1000 words over target. Perhaps I'll save those points for other more specialist articles.

I would also consider the weight of the lens. If you are using lenses to shoot wildlife you usually need telephoto lenses and they come in different weights. Many people get into photography after enjoying taking pictures using smartphones and if they suddenly faced with lens that is heavy, they might lose interest fast.

Yes, very true. Thanks.

Another important factor to consider is minimum focus distance, or maximum magnification ratio. Many of us end up wanting to shoot at much closer distances than we had expected to, only to be held back (literally) by our lens' inability to focus at close enough distances.

The actual magnification ratio is the most important real-world factor to look at here, as it is consistent from camera to camera, no matter what size sensor you are using it with. Do not fall into the trap of thinking that if you have a smaller sensor, then you don't need as much actual magnification - it just doesn't work that way. It's not about how many pixels you can put on the subject, or about how much of the frame you can fill with the subject. Rather, it is about the look you are able to get when shooting from such a close point of view - the way the tiny parts of the subject look in relation to the other tiny parts, from that close perspective ..... and also about how the background looks in relation to the subject when shooting from such a close distance. Magnification really is the thing that matters here, as it directly correlates to the distance you can focus at, for any given focal length.

A magnification ratio of 0.5:1 is very good and will allow pleasingly close-up photos of flowers, butterflies, watches, jewelry, detail abstracts, etc. A magnification ratio of 0.4:1 is okay and will provide decent results for most of these types of small subjects, but 0.5:1 will allow you to do more and do it better.

Remember, nothing is actually macro unless it gives a full 1:1 magnification ratio. Beware of lenses using the word "macro" in their name that aren't actually macro lenses. Most of us don't need true macro for what we want to shoot, but the misuse of the term is something to at least be aware of.

That is true. My macro lens is 2:1 (not 1:2) so double the magnification of 1:1 macro. Does that then become micro photography?

Have you ever seen Ethan Beckler's amazing work?

https://www.flickr.com/photos/194954457@N05/albums/72177720296513917/with/51868215374 You might need to copy and paste that into your address bar as the comments section breaks the link,

He does fabulous shots of sand grains too.

https://www.1of1images.com/

I wasn't writing about actual, or true, macro photography, because I do not think that falls within the primary context of this article. I just brought up MFD and magnification because for many of us, it is something that can be important in an all-around lens, or in a telephoto lens or portrait lens.

Ethan's macro work is spectacular! Thanks for sharing that.

As for 2:1 being micro photography, I guess that depends on what your working definition of "micro" is, within a photography context.

I have often read that "macro" pretty much has a definite accepted definition as anything equal to or greater than 1:1 magnification. So of course when you use your lens at 2:1 you are doing true macro, just like you are when you use it at 1:1. Of course there are statements you can find that contradict this, but generally greater than or equal to 1:1 is the accepted definition/standard by which macro work is defined.

I also often read that "micro" is not so neatly defined, or universally agreed upon; that it means different things to different people and there is no real meaning or definition that we can go by because its use so widely varies. So "micro" pretty much just means whatever somebody thinks it means or wants it to mean. Often it is used as a direct synonym for macro, although that is by no means standard or widely accepted.

Thanks, Tom.