The most popular telephoto lenses cover angles of view from between about 34 degrees (70mm in 35mm format) to eight degrees (around 300mm). Interestingly, the longer lenses have special characteristics that set them apart from shorter teles and require more skill and technical knowledge to be used optimally. In this feature we’ll concentrate on lenses with focal lengths greater than 200mm.
A 300mm lens used on a Canon EOS-1D mark IV for sports photography. An aperture of f/11 was chosen to maximise depth-of-field without compromising image sharpness, while ISO was set to 800 to enable a shutter speed of 1/1000 second to be used. The subject was just over 28 metres from the photographer.
Long tele lenses are most commonly used for sports and wildlife photography, although they can be used for many other applications. Our primary focus will be on shooting with long and extreme telephoto lenses, covering issues to consider when choosing these lenses, what to expect in your photos, and techniques to employ.
Tele lenses are characterised by a perceived ‘compression of perspective’. Interestingly, the perspective isn’t actually ‘compressed’. Perspective is determined by your position with respect to the subject when the shot is taken.
Shooting with a tele lens usually means you’re some distance from the subject. Because distant objects cover much more of the lens’s angle of view than they would with a wide-angle lens, the narrow angle of view causes subjects close to the camera to appear similar in size to objects much further from the photographer. As a result, objects at different distances appear to be closer together when photographed with a long lens.
Tele lenses usually become longer, larger in diameter and heavier as their focal length increases. Beyond a certain point (which varies with the photographer’s strength and experience), a lens becomes difficult to use hand-held. Tripods are normally required to prevent camera shake.
Thanks to image stabilisation, hand-held shooting is possible with these lenses, particularly those in the 200mm to 400mm range; You just need to know how to keep them steady while you’re shooting with them.
Diffraction, Optimum Aperture Range and ISO Setting
Photographers often stop down lens apertures to gain greater depth-of-field in images and/or increased image sharpness. However, although this can yield benefits with wide-angle and normal lenses (as long as you don’t stop down beyond about f/13), with telephoto lenses it’s often less successful because of diffraction limits in the optical system.
Diffraction occurs when the rays of light are forced through a tiny lens aperture, which causes them to diverge and begin to interfere with each other. Image sharpness is progressively reduced as the aperture becomes smaller.
Most lenses perform best between one and three f-stops down from their maximum aperture. Between this point and the point at which the effects of diffraction become visible lies a ‘sweet spot’ range of apertures where the lens performs best.
For consumer tele lenses with focal lengths between 200mm and 500mm and maximum apertures between f/4 and f/5.6, the sweet spot usually extends from f/8 to f/11, which is only one f-stop. (In most cameras, apertures are adjustable in increments of 1/3EV so there are actually four aperture settings to choose from within this range: f/8, f/9, f/10 and f/11.)
With professional lenses, the sweet spot is usually closer to the maximum aperture and, since the maximum apertures of professional lenses can be a full f-stop (or slightly more) wider than consumer lenses, the photographer can use lower ISO settings and gain greater control over depth-of-field in shots. However, some of these lenses begin to lose sharpness at f/4 or f/5.6, which creates additional problems.
High-quality consumer teles can match the sharpness of professional lenses when used within their sweet spots. And this is where ISO plays an important role. While it’s possible to hand-hold some long tele lenses, if your camera produces noisy images at high ISO settings, a tripod will be essential if you want the best image quality.
Unfortunately, it can be difficult to use a tripod for candid and street photography and sports and wildlife shooting where the photographer needs to be able to move quickly between several vantage points. Hand-holding the camera is the only option.
When shooting hand-held, fast shutter speeds are required to minimise camera shake (a major source of image blurring with long lenses). The general rule that you should use the reciprocal of the lens focal length as the shutter speed (eg, 1/100 second for a 100mm lens) might apply for short and medium teles but is probably not fast enough with longer focal lengths.
Although experienced photographers may be able to hand-hold long lenses with slower shutter speeds, for most amateurs using lenses in the 200mm to 300mm band, a minimum shutter speed of 1/1000 second is advisable. For longer lenses, shutter speeds of 1/2000 second and higher can be necessary.
Stabilisation, particularly when built into the lens, can improve your chances of getting sharp images at slightly slower shutter speeds. Most systems claim between two and four f-stops of compensation, although they are more effective with fine jitter than larger movements. They also work better with single shots than for bursts, so you can’t rely on stabilisation to provide perfect sequences of sharp shots when photographing fast-moving subjects.
Unless your subject is brightly lit, you will probably require fairly high ISO settings ““ and this means using a camera with good performance at ISO settings of 6400 or higher. Digicams with ultra-zoom lenses are unlikely to produce ultra-sharp images that can be enlarged beyond A4 size at high sensitivity settings. Some non-reflex interchangeable-lens cameras will also struggle.
A useful strategy is to set the ISO to the Auto position but limit the upper ISO setting to prevent the camera from straying into the range where image noise becomes apparent. (Most mid- and upper-level DSLRs provide these restrictions.) This enables you to shoot with the aperture-priority AE mode, keeping an eye on shutter speed settings. You could also use shutter-priority and carefully monitor aperture settings to keep exposures within the ‘sweet spot’ of the lens.
For lenses longer than about 300mm, the best results will come from a camera with a large sensor and large photosites. Used strictly within their ISO and resolution limitations, cameras with smaller (APS-C and Micro Four Thirds) sensors can also produce satisfactory image quality.
Once again, it’s a question of balancing pros and cons and taking account of the magnifying effect of smaller APS-C sensors on lenses designed for ‘full frame’ DSLRs. In many cases you will obtain sharper images edge-to-edge with these pairings because the smaller sensor doesn’t use the periphery of the lens’ field of view. This eliminates some edge and corner softening.
Sensor resolution also plays a role in the end result. The larger the photosites, the more light the sensor can capture and the higher the image signal is to the background noise (which reduces image sharpness). But the higher the sensor’s megapixel count, the sharper the lens must be to produce good results.
Once again, it’s a case of balancing signal/ noise against resolution. Many lenses (including some with comparatively high price tags) can’t match the resolution required by today’s 20-megapixel plus cameras.
A sharp action shot taken with a stabilised 300mm lens on Canon EOS 40D (480mm focal length equivalent in 35mm format) using an aperture of f/10 and shutter speed of 1/800 second with ISO 400.
Unless your subject is brightly lit, you will probably require fairly high ISO settings ““ and this means using a camera with good performance at ISO settings of 6400 or higher. Digicams with ultra-zoom lenses are unlikely to produce ultra-sharp images that can be enlarged beyond A4 size at high sensitivity settings. Some non-reflex interchangeable-lens cameras will also struggle.
A useful strategy is to set the ISO to the Auto position but limit the upper ISO setting to prevent the camera from straying into the range where image noise becomes apparent. (Most mid- and upper-level DSLRs provide these restrictions.) This enables you to shoot with the aperture-priority AE mode, keeping an eye on shutter speed settings. You could also use shutter-priority and carefully monitor aperture settings to keep exposures within the ‘sweet spot’ of the lens.
For lenses longer than about 300mm, the best results will come from a camera with a large sensor and large photosites. Used strictly within their ISO and resolution limitations, cameras with smaller (APS-C and Micro Four Thirds) sensors can also produce satisfactory image quality.
Once again, it’s a question of balancing pros and cons and taking account of the magnifying effect of smaller APS-C sensors on lenses designed for ‘full frame’ DSLRs. In many cases you will obtain sharper images edge-to-edge with these pairings because the smaller sensor doesn’t use the periphery of the lens’ field of view. This eliminates some edge and corner softening.
Sensor resolution also plays a role in the end result. The larger the photosites, the more light the sensor can capture and the higher the image signal is to the background noise (which reduces image sharpness). But the higher the sensor’s megapixel count, the sharper the lens must be to produce good results.
Once again, it’s a case of balancing signal/ noise against resolution. Many lenses (including some with comparatively high price tags) can’t match the resolution required by today’s 20-megapixel plus cameras.
This shot, taken with a Sony 500mm f/8 lens on an SLT-a55 camera, shows how useful longer lenses can be for taking close-ups of wildlife (in this case a female red-Tailed Black co*ckatoo).
Using Telephoto Lenses
Most of the time, tele lenses are simply used to magnify subjects in the camera’s field of view and allow photographers to be more selective with what they include in shots. Longer lenses also allow close-up shots that would not otherwise be possible, particularly with flighty subjects.
This shot was taken with a 70-300mm lens on a Canon EOS 1100D body. The long focal length (equivalent to 352mm in 35mm format) provided a good camera-to-subject distance for a candid shot.
Wide camera-to-subject distances provided by a telephoto lens are valuable to wildlife photographers because the presence of humans can influence the behaviour of wild animals and birds. Longer focal lengths also let you defocus backgrounds to make the subject the main focus of the shot.
Missing focus by even a couple of centimetres would have made this shot a discard instead of a keeper because the lens would have focused on the vegetation instead of the bird’s eye. Canon EOS 40D with EF 70-300mm lens at its maximum aperture of f/5.6 at 300mm.
Longer lenses are almost as valuable for candid portraiture and street photography. Most people’s behaviour changes once they notice someone is taking their photograph and this can destroy the naturalness of shots. The distance advantage a long lens provides can make a photographer less noticeable than they would be with a shorter lens.
A 400mm lens was used on a Nikon D3 body for this candid portrait. The long lens provided enough distance between the camera and the subject for the child to be unaware of being photographed. The f/5 aperture setting was small enough to render the face in acceptably sharp focus but also produced attractive de-focusing of the foreground and background, concentrating the viewer’s attention on the subject.
Shooting with a shallow depth of field presents a specific technical problem: where should you focus? Choosing the optimum plane of focus in the subject is critical. For shots of people and wildlife, the focus must be on the subject’s eyes. Being even slightly off the mark with a shallow depth-of-field will make a picture unusable.
Longer focal lengths can be an effective way to emphasise congestion in a crowded scene or to illustrate the density of objects in an environment. Stop the lens aperture down a little more than you would for portrait shots to prevent objects in the background from being blurred unrecognisably. (Raising the ISO setting is often necessary.)
Telephoto lenses can impart a sense of depth to a scene, particularly when you take advantage of aerial perspective (where contrast and colour saturation decrease with distance). Canon EOS 1100D with 300mm focal length (equivalent to 480mm in 35mm format).
Long focal length lenses can also be used for other types of photography where their native characteristics lend a different touch to more traditional perspectives. Telephoto lenses can yield interesting shots for both landscapes and cityscapes. The apparent compression of distance can be used creatively in a number of ways.
A common way to use a long lens when photographing landscapes is to emphasise structural layers in scenes. This adds an almost three-dimensional feeling to what is actually a two- dimensional picture. It’s particularly effective when the scene contains clouds, mist or smoke.
A 300mm lens used on a Canon EOS 5D Mark II body to capture layers in a landscape. ISO 400, 1/60 second at f/8 using a tripod to steady the camera.
Some long telephoto lenses ““ particularly telezooms with ‘macro’ modes ““ can also be used for close-ups. Even though they seldom provide true 1:1 reproduction ratios, they do offer a good working distance between camera and subject that can produce worthwhile results.
This shot was taken with a 300mm lens on a Sony DSLR with an APS-C sensor, which made the focal length equivalent to 450mm in 35mm format. The focus was on the bird in the centre of the frame, nearest to the camera. choosing an aperture setting of f/9 minimised the background de-focusing to emphasise the population density in the shot.
Primes vs Zooms
While specialist sports and wildlife photographers usually prefer shooting with prime (single focal length) lenses, most enthusiasts and many generalist professional photographers opt to shoot with zoom lenses. Zooms are more versatile, easier to carry and often lighter and more manoeuvrable than prime lenses. They’re usually also cheaper.
From a performance viewpoint, the main difference between primes and zooms is edge-to-edge sharpness. Primes tend to be sharper over the entire field of view. Zoom lenses may be able to match some primes’ sharpness in the centre of the frame but can fall off towards the corners of the frame, losing up to 20% of resolution at the corners.
Does this matter?
It does if you’re a landscape photographer. People expect landscape shots to be sharp throughout the frame. Edge sharpness is seldom an issue for sports, wildlife and candid photographers, although centre sharpness is.
Reduced resolution towards the periphery of the frame is normal in shots with shallow depth-of-field. Even though few telephoto zooms are perfectly sharp edge- to-edge, as long as their centre resolution is high, their performance will be adequate for these applications.
Resolution can also vary with focal length. Unfortunately, few zooms produce equal resolution throughout their focal length ranges. Once again, it becomes a matter of finding the ‘sweet spot’ in the zoom range. The best way to do this is to study lens tests, of which there are many online.
A 55-300mm zoom lens used at 300mm on a camera with an APS-C sized sensor enabled this close-up to be taken of a bee in action. ISO 400, 1/500 second at f/5.6, the maximum aperture available for the focal length setting.
Extended-range zooms (sometimes called ‘super- zooms’) that span from wide-angle to telephoto focal lengths may be convenient when you want to carry just one camera and one lens. However, there are prices to pay for this convenience:
- They’re usually slow. Typical maximum apertures range from around f/3.5 at the wide end to f/5.6 by about the 200mm position. That’s more than two f-stops slower than an f/2.8 prime, which is the difference between using ISO 800 and ISO 6400 in low light.
- Smaller maximum apertures can make it difficult to blur busy backgrounds or foregrounds and isolate the subject, particularly when the camera’s sensor is small.
- Image quality can be compromised by the need to design lenses that are small, light and cheap enough to be popular.
This is an excerpt from Photo Review Issue 52.
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