Telephoto lenses are a vital tool for many photographers, particularly when covering wildlife, sport or news, but they can be a substantial investment. It's therefore important to consider what you need your lens to do, both now and in the future, to ensure you make the right choice and can shoot the kind of imagery you want as the scope of your work progresses.

For Spanish wildlife photographer and Canon Ambassador Marina Cano, telephoto lenses form the core of her kitbag. With over 16 years' experience of shooting nature, Marina has learnt what she needs from her lenses, whether she's shooting at Cabárceno wildlife park close to her home in Santander, Spain, or leading photographic safaris in Namibia or Kenya. Reliable, versatile glass ensures she is able to capture tender moments in the wild, in the fine art portraiture style for which she's become known, and share them with her 28,000 Instagram followers.

1. Pick what you need for your subjects

When choosing a telephoto lens for shooting wildlife, it's important to bear in mind what you're likely to be shooting, says Marina. How far away will your subjects be? Are they likely to be in a fixed position or on the move? "Your destination will give you an idea of how far away the wildlife could be, and that will decide the focal length," she says. "Then your own style, together with the lens quality, will help you decide on a lens."

If you're shooting from a static location, such as a hide, it's especially important to consider the minimum focusing distance of a fixed telephoto lens to ensure continuous coverage. For example, the Canon EF 300mm f/2.8L IS II USM lens focuses down to two metres, while the Canon EF 600mm f/4L IS III USM lens focuses down to more than twice that (4.2 metres). If an animal is coming towards you, you might be better off using a 300mm lens.

Marina loves the flexibility she gets from telephoto zooms and encourages her photography students to use them because they make it easier to frame fast-moving subjects. "Using the Canon EF 200-400mm f/4L IS USM Extender 1.4x lens gives you the optical quality of a fixed focal length lens and combines it with the versatility of a zoom," she says. "The zoom helps you to compose your shot, especially if you cannot move from your position, for example if you're in a car on safari, or if your subject is moving further away or getting closer."

2. Consider weight and size

Telephoto lenses are notoriously unwieldy. Historically both bulky and heavy, they are often considered hard to transport and work with. Yet, within the telephoto category there is a wide divergence in focal length and associated weight and, as optics technology progresses, lenses are coming in smaller packages yet performing better than previous iterations.

3. Seek out Image Stabilization for sharper handheld shots

As telephoto lenses continue to become smaller and lighter, shooting with them hand-held has become a more viable option. However, these lenses are still large enough for camera shake to remain a potential problem. This effect is magnified at longer focal lengths, making good quality Image Stabilization (IS) critical for maximum sharpness.

"Stabilization is really important when hand-holding super telephoto lenses, such as the Canon EF 600mm f/4L III USM lens, or in low-light conditions, when you need to match the shutter speed with the focal length reciprocal, such as 1/600 sec for a 600mm lens," says Marina. With powerful IS built into professional grade telephoto lens ranges, such as the Canon L-series lenses, wildlife photographers can select different modes depending on whether they are shooting static animals or tracking moving ones.

The Canon EF 600mm f/4L III USM lens has 5-stops of IS to keep things sharp, while the Canon EF 200-400mm f/4L IS USM Extender 1.4x has 4-stops of IS built-in, and the Canon EF 300mm f/2.8L IS II USM lens has 3.5-stops of IS.* This is particularly beneficial when shooting animals that are active at dawn and dusk – in low light, shutter speeds need to be slower for a good exposure, meaning potentially more risk of blurring due to camera shake.

The IS in these lenses, coupled with fast autofocus from ring-type Ultrasonic motors, allows you to easily keep up with any fast-paced action. "The Canon EF 600mm f/4L III USM and Canon EF 300mm f/2.8L IS II USM are my most used lenses for a reason," says Marina. "The autofocus is precise and very fast. I also love their performance in the out-of-focus areas in the background."

4. Demand edge-to-edge sharpness

Marina's style of wildlife photography captures great detail in her subjects, from the crease on the back of a gorilla's hand to the fine hairs on an elephant's trunk. That's down to how close she can get to wildlife, and the clarity with which she can focus. These small details on an animal's skin develop intimacy in photography, so choosing a lens that can resolve small details with precision is key.

"Quality, together with nearness, is essential in my work," she says. "The Canon EF 600mm f/4L III USM lens allows me to capture details in my images such as hairs and skin texture in a brilliant way. The most important factor with this lens is the proximity it gives me."

With Super Spectra Coating (SSC) and Air Sphere Coatings (ASC), the Canon EF 600mm f/4L III USM lens is designed to minimise flare and ghosting across the lens elements for increased clarity. Meanwhile the Canon EF 300mm f/2.8L IS II USM uses SubWavelength Coating (SWC) to prevent unwanted reflections and flare. Plus, the 9-blade aperture diaphragm design in both these lenses produces a smoother bokeh in out-of-focus areas in the foreground and background, to complement a sharp subject.

5. Be prepared with weather sealing and durable build

Shooting the natural world means working in the great outdoors, with all the adverse conditions that can bring. Whether shooting in sandstorms in the desert, dust and rain on the Savannah or freezing conditions in the Arctic, wildlife photographers need to invest in durable lenses with a superior build quality to resist the elements.

Weather sealing is something Marina has fallen back on time and time again in the field and always looks for when choosing her lenses. Waterproofing means that she's able to keep shooting for longer when the weather turns, and can shoot subjects that are more likely to emerge in the wet. "I was photographing bears with their cubs in the springtime using my Canon EF 600mm f/4L III USM lens when it started to rain," she recalls. "I knew I didn't have to worry about the lens getting wet, so I could keep shooting."

The fluorine lens coatings on the front and rear elements of Canon's L-series telephoto lenses make it easy to clean away dust and other particulates, which is helpful when shooting in dusty and arid conditions. A strong rubber ring fixed around the lens mount, as found on the Canon EF 300mm f/2.8L IS II USM lens, also helps to keep dust and debris out of the camera.

* IS figures based on CIPA testing.