Lens Buying Guide

The Micro Four Thirds lenses line-up.

The Process of Choosing a Lens

Buying an interchangeable-lens camera represents a commitment to a system that is centred upon lenses ““ and it’s the lenses that dictate the types of photos you can take. Some systems provide a wider range of lenses to choose from than others so it’s important to take this factor into account when choosing which brand and format of camera to buy.

If we were to produce a flowchart to step you through the process of choosing a lens, the following decisions will provide the quickest, most straightforward way to target which lens to choose from the hundreds of options available:

1. Check the lens mount.
2. Check the sensor format.
3. Decide on the subjects you want to photograph.

Lens Mount

In most cases, one company’s lenses won’t work on another company’s cameras. The reason is that each manufacturer has its own lens mount, which uses proprietary physical and electronic connections.

There are two exceptions to this rule. The first is the Four Thirds System, which is now mainly seen as  Micro Four Thirds (M4/3)  and is based on a ‘universal’ mount. This system has been adopted by Olympus and Panasonic (plus a handful of other companies that mainly produce video equipment) and is supported by so many camera bodies (18 Four Thirds cameras, mostly discontinued, plus 34 M4/3 cameras at last count and still growing) that third-party lens manufacturers (see below) are beginning to design lenses for the format.

The Olympus OM-D EM-1 uses the Micro Four Thirds lens mount. (Source: Olympus)

The second instance is third-party lens manufacturers, like Sigma, Tamron and Tokina, who produce lenses with mounts to suit different camera brands. In most cases, the only difference between the lenses is the mount although, for Sony’s stabilised camera bodies, stabilisation isn’t required in the lenses, enabling them to be lighter and slightly cheaper than the products for Canon and Nikon bodies.

So, bearing in mind that it’s usually best to start with lenses designed for your specific camera, the next factor to consider is the sensor format. This dictates the size of the lens.

Format

The current camera market is awash with different sensor formats, which vary according to size and aspect ratio. The traditional 35mm film frame has been adopted as a reference point because most people are familiar with the angles of view covered by popular focal lengths. Most interchangeable-lens cameras have smaller sensors so it is common practice to provide equivalent or effective focal lengths relative to the 35mm frame size. Smaller sensors apply a ‘crop factor’ or multiplier to provide this relationship.

They may also use a different aspect ratio from the traditional 3:2 ratio of 35mm film, with the M4/3 format having a native 4:3 aspect ratio, based on traditional TV and computer screens. (Most cameras enable photographers to choose from several aspect ratios, which are achieved by cropping the top and bottom of the frame.)

The table below shows the main formats found in today’s interchangeable-lens cameras.

Owners of Canon and Nikon ASP-C DSLR cameras can use all the lenses in each company’s DSLR range on their camera bodies. But, those with ‘full frame’ camera bodies are advised not to use lenses designed for the smaller APS-C bodies because they don’t cover a wide enough imaging circle. Even though the lens mounts are the same, if you fit one of Canon’s EF-S or Nikon’s  DX lenses  on a ‘full frame’ body there is a risk of damage to the reflex mirror because its flange back (distance from the back of the lens to the sensor) is shorter. The corners of images will also be darkened noticeably by the reduced coverage of the lens’s field of view.

Subjects

What subjects do you like to photograph? If you’re a newcomer to serious photography you will probably find this question difficult to answer. Fortunately, camera and lens manufacturers have provided an easy solution in the form of kit lenses, which are bundled with the camera, usually at a very competitive price.

The standard offerings are a single-lens kit with a ‘standard’ zoom lens that covers angles of view from moderately wide to a short telephoto that is suitable for portraiture and a twin-lens kit that adds a telephoto zoom lens that begins where the standard zoom ends and extends the focal length to provide enough magnification for shooting sports action and wildlife. With this pair of zoom lenses there are few types of subjects you can’t tackle.

Kit lenses are a great way to get started in photography and many camera buyers will find they don’t need additional lenses. However, compromises have been made to keep their sizes, weight and price tags as low as possible.

The main problem with kit lenses is lower light transmission, which shows up as a dimmer image in the optical viewfinder (you can adjust the brightness of electronic viewfinders to compensate). This is due to the fact that less glass is used to keep size and weight low. Lenses that let in more light are always larger, heavier and much more expensive.

Kit lenses may also have plastic mounts, again to keep weight and price low. Although modern plastics are durable, they are not as robust as metal. In time, wear will loosen the lens mount and this can affect the alignment of the lens, which will also influence its focusing accuracy.

If you expect to change your gear frequently, buying cheap lenses shouldn’t be a problem, although you can’t expect high re-sale values. If you prefer to keep equipment for a long time (and lenses are a better investment than camera bodies because they are less prone to technological changes), always choose the most durable option.

Once you have moved beyond the snapshooter/hobbyist level you will probably start looking for specialist lenses, such as macro lenses or lenses with flat fields for architectural and landscape work. Alternatively, you may wish to pick a focal length you often use and buy a prime lens to improve image quality and provide greater control over depth of field for a particular type of subject. The following general guidelines apply for popular subject types:

Portraits:  moderate telephoto lenses (equivalent to about 75-110mm in 35mm format);

Landscapes:  wide-angle lenses (equivalent to about 24-35mm in 35mm format);

Sports:  telephoto lenses (equivalent to at least 200mm in 35mm format);

Wildlife:  telephoto lenses (equivalent to at least 300mm in 35mm format);

Close-ups:  many lenses will focus to within about 30cm but if you want to take macro shots only true macro lenses provide life-size (1:1) reproduction;

Underwater:  moderately wide zoom lenses that are compact enough to fit into a housing;

Travel:  consider a single zoom lens that extends from moderate wide angle to telephoto.

Nikkor lenses line-up. (Source: Nikon)

Stabilisation

Unless your camera has stabilisation built into the camera body, stabilised lenses are recommended for lenses with focal lengths longer than about 100mm in 35mm format. So far the only camera manufacturers to have integrated stabilisation into their cameras are Olympus, Pentax and Sony (only some cameras), although Panasonic recently added it to its GX7 model.

When checking out lenses, look for clues like ‘IS’, ‘OS’, ‘OIS’ and ‘VR’ (for Vibration Reduction) in the lens name. Many lenses provide two stabilisation settings, one for photographing stationary subjects and the other for moving subjects. The stabilisation system in some lenses must be switched off when you mount the camera on a tripod; other lenses detect tripod mounting automatically.

Focusing Motors

Most high-performance lenses are driven by  ultrasonic motors (USM) or high-precision stepper motors, which move internal elements to adjust focusing and/or change the zoom range. These AF drivers operate very quickly and quietly, with barely detectable stops and starts and minimal power drain, making them particularly suitable for use when recording movies.

Cheaper lenses tend to use micro motors, which are generally noisier and often slower. The camera’s built-in microphones will often pick up the sounds made by camera adjustments and record them on movie soundtracks. Autofocusing and zooming are the leading sources of this unwanted noise.

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