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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.