Convenience zoom lenses

When you’re hiking in challenging terrain, the less weight you carry the easier you will find it. All-in-one zoom lenses are ideal for such situations. This shot was taken with a focal length of 24mm using an 18-200mm lens on an APS-C DSLR camera.

There are many reasons for using just one lens on your camera ““ and not all are economic. All-in-one zoom lenses usually cover all the angles of view snapshooters are likely to require. Travelling photographers are attracted to the so-called ‘convenience ‘zooms because they provide a camera-plus-lens combination that is compact and easy to carry, yet versatile enough for most situations. It’s also less likely to attract thieves in crowded areas.

Tamron was the first to popularise ‘convenience ‘zooms with its 28-200mm lens, which was just wide enough at 28mm to be considered wide angle and just long enough at 200mm to qualify as a telephoto lens. Introduced in 1992, this lens was designed for 35mm film SLRs. It was followed in 2005 with the AF 18-200mm f/3.5-6.3 XR Di II LD Aspherical [IF] Macro lens, the first truly all-in-one zoom lens for digital SLRs, which was designed for cameras with APS-C sized sensors.

Today almost all lens manufacturers have at least one convenience zoom lens in their ranges, the majority being for entry- and enthusiast-level cameras. Many cover a wider zoom range than the 7.1x offered by the original Tamron zoom. with ‘super-zoom’ lenses often spanning a range of up to 17x magnification. (Even larger zoom ratios have been included in the fixed lenses on some digital cameras and camcorders.)

Convenience zoom lenses are ideal for today’s entry-level DSLR and Compact System Cameras (CSC), which usually have relatively compact and lightweight bodies. Being designed mainly for travel, these lenses are often small and light and provide a much better balanced package than a pro-level zoom lens. They also fit into a smaller bag than a twin-lens kit that includes standard and telephoto zooms.

Typical Focal Lengths

Convenience zoom lenses span different focal length ranges, depending on the format of the camera they are fitted to. The table below shows typical focal length ranges for the most popular interchangeable-lens camera formats.

This illustration shows the zoom range of a typical 18-200mm zoom lens, which provides just over 11x magnification. (Source: Tamron.)  

Benefits

The benefits of all-in-one lenses are easy to define. There’s less weight for you to carry around; you can easily pack a DSLR plus lens into a holster-style pouch and sling it across your shoulder where it’s easily accessible at any time. It’s kinder to your back, your shoulder and also your wrists when you’re shooting, and more secure than a backpack in city environments.

With only one lens there’s no need to change lenses. This means the camera’s sensor is never exposed so you don’t have to worry about dust getting into your camera. In addition, you won’t miss shots through having to change lenses when a less-than-ideal lens is fitted.

There’s no need to worry about carrying different filters for different lenses and there’s only one lens cap to keep track of. And you can vary your views of subjects by simply zooming in and out. Most of these lenses also support macro-like focusing for close-ups, although few of them offer true 1:1 reproduction ratios.

Financially, the differences are not so great and a body plus all-in-one zoom may end up costing more than a twin-lens kit. It’s possible to buy, say, an 18-200mm f/3.5-6.3 lens for an entry-level DSLR for less than $500 or a 14-150mm f/4-5.6 lens for an M4/3 camera for roughly $750. These prices are similar to the cheapest twin-lens kit (which includes the camera body) .

Tamron’s 16-300mm f/3.5-6.3 Di II VC PZD Macro lens has one of the longest zoom ranges on the market yet is remarkably small and light. It combines a sophisticated optical design with the latest stabilisation and autofocusing technologies.

Other options	Most popular range	Focal length crop factor	Sensor size	Format
24-105mm, 28-135mm, 28-300mm	28-200mm	1x	36 x 24 mm	‘FX’
18-135mm, 18-250mm, 18-270mm	18-200mm	1.5x to 1.6x	~ 23.5 x 15.7 mm	‘DX’
14-150mm	14-140mm	2x	17.3 x 14.0 mm	M4/3
n.a.	10-100mm	2.7x	13.2 x 8.8 mm	‘CX’

Compromises

Sadly, with convenience comes compromise. Although reductions in imaging performance are not as great as they used to be (thanks largely to improvements in image processing and stabilisation technologies), there are some sacrifices you must accept when you opt for an all-in-one lens.

Lens speed is the first factor you’ll forgo. To ensure lenses are portable, manufacturers must design lenses with smaller elements. Smaller elements means less light is captured, which means the brightness of the scene you see in the viewfinder is reduced ““ unless your camera has an electronic ‘finder.

It’s rare for the maximum apertures of convenience zooms for APS-C DSLRs to be greater than f/3.5 at the wide end and f/5.6 is a typical maximum aperture at 200mm. Maximum apertures can be even smaller for M4/3 cameras.

As well as affecting the brightness of optical viewfinders, smaller maximum apertures reduce your ability to control depth-of-field in shots. Convenience lenses can make it more difficult to reduce ‘busy’ backgrounds to a smooth and attractive blur.

Accordingly, you will probably obtain greater front-to-back focus depth than you would like. In addition, it can be more difficult to focus close to infinity than it is with shorter zoom lenses.

Reductions in image quality will become apparent when you compare pictures from an all-in-one zoom lens with other zooms that cover shorter focal length ranges. You will probably notice some loss of edge sharpness in shots, particularly at wider aperture settings.

Most lenses (convenience zooms included) provide maximum sharpness between one and two f-stops down from maximum aperture. Subjectively, edges of shots from prime lenses and short zooms will probably look sharper from about f/5.6 to f/22, although fast lenses usually exhibit edge softening at the widest aperture settings.

Diffraction usually begins to reduce lens acuity from about f/8 in most lenses, although its effects may not become apparent for subjective assessments of images until about f/11 with prime lenses and fast, high-quality short zooms. Prime lenses and short zooms will inevitably be sharper in the centre of the field at all aperture settings than all-in-one zooms. Convenience zooms can seldom match their performance at any aperture setting, although differences may not be noticeable until images are compared side-by-side.

Distortions are usually very obvious in zoom lenses that cover an extended focal length range. Barrel distortion (when straight lines become bowed outwards) occurs at wide angles with pincushion distortion (when straight lines are pinched in towards the centre of the frame) at the telephoto end.

Although most modern cameras provide in-camera correction for both types of distortion, it is difficult to correct when the lines aren’t rendered totally straight. This can happen with cheaper lenses that cover an extreme zoom range. The central and edge areas can have different distortion patterns at the long end, with the corners being slightly pin-cushioned and the centre slightly barrelled. At the wide end, the barrel distortion may be slightly wavy.

Reliability is another factor that may be compromised. Zoom lenses are generally packed with mechanical components and electronics, and the longer the zoom range the more the internal mechanisms are required to move. Eventually the components supporting the zooming elements will wear out. (Focusing elements move too, but not as much, so they tend to last longer.)

Being relatively small and light, convenience lenses are handy for shooting in urban environments, where longer focal lengths enable you to record close-ups of people without attracting attention. This shot was taken with a focal length of 120mm using a 14-150mm lens on a M4/3 camera.

There’s no risk of dust entering your camera if you don’t need to change lenses. And there’s only one lens cap to keep track of. This shot was taken in a dusty environment using a 24-105mm lens with the focal length at 45mm on a ‘full frame’ DSLR camera.

Smaller maximum apertures can make it difficult to shoot in dim lighting. This shot was taken just on sunset with a 14-150mm zoom lens on a M4/3 camera using the maximum available aperture of f/5.6 at ISO 3200. The camera’s image stabilisation system was pushed hard to maintain sharpness at 1/20 second.

It’s easy to obtain front-to-back focus depth in scenes with small apertures and normal angles of view. This shot was taken with a focal length of 20mm using a 14-150mm lens on a M4/3 camera.

What to Look For

Built-in stabilisation is a necessity in all-in-one lenses ““ unless your camera includes body-integrated sensor-shift stabilisation. While you may not need its assistance at wider settings, from about the mid-point in the zoom range your ability to hold the camera steady will be stretched in even slightly lower light levels than normal. A good stabilisation system with three- or four-stop compensation should enable you to take sharp pictures hand-held at shutter speeds down to about 1/30 second with a 200mm focal length.

Fast, accurate autofocusing becomes increasingly important with longer focal lengths because depth of field is reduced. While standard micro-motor autofocus systems can usually focus accurately, they can be relatively noisy and may not be particularly fast. Lenses with ring-type ultrasonic motors (designated ‘USM’ , ‘HSM’ or ‘SWM’) or Piezo-electric Drive mechanisms (‘PZD’) are very fast, almost silent and have the added advantage of supporting full-time manual focus over-ride.

Using All-in-One Lenses

Although they can be a useful part of your kit, particularly when you’re travelling, convenience zooms require you to pay a lot more attention to the shots you’re taking than other lenses, largely because they are equivalent to carrying a wide range of focal lengths. You still have to decide which focal length setting is best for the subject, even though there’s no need to change lenses to obtain different focal lengths.

Careful shot composition can overcome some of the compromises convenience zooms enforce. Because they make it easy to zoom in on distant subjects or out when subjects are a bit too close some photographers will stay in one place and zoom instead of shifting position with respect to the subject. The end result is a series of shots with the same perspective, which is boring.

Think about where you are and how it affects your relationship with the subject. Use your feet; change your position, vary the difference between you and the subject. That way you will produce more interesting and satisfying images that will enrich your portfolio enormously.

Pay attention to backgrounds and choose shooting positions that will keep them as plain and unobtrusive as possible. Don’t expect beautiful bokeh from lenses in this category, particularly at wider angles of view. The relatively small maximum apertures make it very difficult to obtain out-of-focus backgrounds, particularly at shorter focal lengths.

Step back and swap to a longer focal length to improve subject isolation. If the lens has a macro setting, use it for close-ups. And fill the frame with the subject to make choppy backgrounds as small a component in the frame as possible.

Work within the limitations of the lens technology. Don’t be afraid to increase the ISO setting in dim lighting. Use a tripod when necessary and be prepared to switch to manual focusing when there’s insufficient light for the camera’s autofocusing system to use.

If you fill the frame with the subject, the problem of unattractive backgrounds can be largely solved. This shot was taken with a focal length of 150mm on a M4/3 camera using a 14-150mm lens.

Try to compose shots with minimal background distractions.

Choppy backgrounds are almost inevitable when you record small subjects with mid-range focal lengths, even at wide aperture settings. This shot was taken with a focal length of 85mm using an 18-135mm lens on an APS-C format DSLR.

Excerpt from Lenses Guide.