Which Telephoto Lens and What for? - Page 3: Using Teleconverters

Which Telephoto Lens and What for? - Page 3: Using Teleconverters

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Article Index
Which Telephoto Lens and What for?
Page 2: Choosing a Lens (cont.)
Page 3: Using Teleconverters
Page 4: Notes and References
All Pages

Using Teleconverters

It is a practical joke between bird photo shooters that, regardless of the focal length of your lens, there are still some mm missing at the long end. Wild animals try to keep their distance from all intruders in their natural habitats, especially the ones holding huge black or white telephotos. At some point we all found out the hard way that our pride and glory of a lens was simply not long enough. One solution is to get a longer tele but this, as indicated, may not be a good option for a variety of reasons. A considerably cheaper alternative is to get a teleconverter. No matter which telephoto lens you have, sometimes using a teleconverter is the only way to capture a specific scene adequately.

A teleconverter (or doubler) is a secondary lens which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image obtained by the objective lens (the telephoto lens). For example, a 2× teleconverter enlarges the central 12×18 mm part of an image to the size of 24×36 mm in the standard 35 mm film format. Teleconverters are typically made in 1.4×, 1.7×, 2× and 3× models. (14)

The use of a 2× teleconverter results in doubling the focal length of a lens. A side effect of this is that the intensity of the light reaching the film or the sensor of the camera is decreased by a factor of 4 (the equivalent of doubling the focal ratio) while the resolution is also decreased by a factor of 2.

Teleconverters work similarly to a telephoto group of a proper telephoto lens. A teleconverter consists of a group of lenses which together act as a single diverging lens. The location of a teleconverter is such that the image produced by the objective is located behind the teleconverter at a distance smaller than its focal length. This image is a virtual object of the teleconverter which is then focused further away and thus enlarged. For example when a single negative lens is placed so that the image formed by the objective is located in the midpoint between the lens and its focal point the lens produces the image in its focal point enlarging it two times thus acting as a 2× teleconverter.

When used with somewhat slow lenses teleconverters may reduce the effective aperture to such a degree that the camera's autofocus system will no longer work; depending on the camera system, this may range from f/5.6 to f/8. The camera autofocus system usually delivers good results with lenses up to f/5.6. At maximum apertures smaller than that (f/8 or smaller) the amount of light entering the camera is too little for the autofocus system to detect phase contrast quickly and work.

Dedicated teleconverters only work with a limited number of lenses, usually telephoto lenses made by the same manufacturer. Using a teleconverter with an existing high quality lens is less expensive than acquiring a separate, longer telephoto lens. On the downside, as the teleconverter essentially magnifies the existing image circle as captured by the lens, it also magnifies any aberrations.

The teleconverters produced nowadays can communicate seamlessly with the lens and camera, particularly when they are made by the same manufacturer.  Older models sometimes prevent the camera’s auto exposure and auto-focus modes from operating. It is also important to remember that

  • not all teleconverters work well with all lenses,
  • teleconverters are most useful on fast lenses, or when taking photos in bright light,
  • they generally work better on fixed focal length lenses than zoom lenses and
  • using them with some lenses (such as the Nikkor 80-400mm f/4.5-5.6 VR or the Nikkor 18-200mm f/3.5-5.6 VR) is not recommended

Teleconverters offer a cheap alternative to really long focal length lenses which usually cost a fortune. They are small so they can fit in your pocket, they are light so you do not have to worry about the overall weight of your gear increasing by much. However, they are a sort of “emergency” lenses, in the sense that they are meant to allow you to shoot something which your “real” lens cannot reach – although at an expense. You have to keep in mind that they are essentially a second set of glass elements slotted between - and interfering with - your expensive prime telephoto and the sensor. This means that the resulting image will always be inferior to the one produced by the prime lens alone. The larger the magnification of the teleconverter lens the more the image quality gets downgraded.

It is worth noting that the higher the quality of your lens the less noticeable the adverse effects of using a TC will be in the final product (photo). The so called ‘exotic’ lenses usually outperform the sensor of the camera in terms of resolution. Accordingly the difference in the optical quality (due to the decrease of resolution by the factor of the TC) of the photo will be minimal, if at all noticeable, if a combination of a good quality prime with a good quality 1.4x TCs is used for a shot. When an 1.7x TC is used the image quality gets affected but a top quality prime (or zoom) lens will still give very good – or even excellent -results. With a 2.0x TC things get noticeable worse. Most photographers try to stay within the 1.4-1.7x range to ensure that the image quality is still very high. We have not met anybody using a 3x TC to get their views on the subject but we feel this should only be done if you desperately need the photo even if the image quality is poor.

We need to re-iterate that in photography the final result (i.e. the quality of the photo) is affected by a combination of factors rather than  simply the quality of a lens or a camera. Depending on the quality of the sensor and the way this compares with the resolving power of the lens mounted on the camera the use of a TC will affect the final product (photo) differently. 

In some cases TCs are really the only option available. As indicated, one such case is when the subject is so far away that your longest lens cannot deliver an image of an acceptable size. Another case is when there are more chances of taking a good quality photo using a lighter combination (camera+TC+shorter tele) than a heavier combination (camera+longer tele), particularly when appropriate support is not available.

When using TCs it is important to remember to adjust the exposure of the camera to compensate for the change of the focal length of the lens. Sure enough, the meter of the camera will recognize that the light hitting the sensor has diminished. This, however, is not enough.  As indicated, the minimum shutter speed for handholding a lens is 1/focal length in mm. When a 1.7 TC is attached to a 300 mm lens the lens effectively becomes a 510mm one. Thus, the previously sufficient 1/300 speed is now insufficient; a speed of 1/600 is the minimum required to handhold the lens. Opening the lens up may be an alternative but this is not usually sufficient because the maximum aperture has also been affected by the use of the TC (assuming you have a really fast tele, with a maximum aperture of f/2.8, the use of a 1.7TC will make this f/4.8 (1.7x2.8)). In practical terms, the attachment of the 1.7 TC is equivalent to stopping your lens down by 2.5 f/stops. This makes a massive difference while shooting. Though it is relatively common to be able to get an exposure of 1/300 at f/2.8 even at basic ISO you will need really bright light to get 1/600 at f/4.8.  The solution is to raise your ISO settings sufficiently to get the speed required. While doing this make sure you do not push your camera out of the acceptable ISO limits for it.

Techniques - Strategies

As one would expect, these differ depending on the tele lens in use. A 200 mm weighing 800grams is pretty different to a 600mm weighing 5500grams. There are certain things which are considered vital, however, when using tele lenses. It is up to individual photographers to consider the extent to which these are applicable in their case.

The main issue when using long teles is how to get sharp photos. There are three kinds of movement affecting a photo. The first originates from the camera. The second originates from the photographer (e.g. the trembling hands or simply your heart beat. Finally, the third kind of movement originates from the subject.

1.    Minimizing camera shake

So we found our subject, composed the photo and we are ready to shoot using a 400mm lens. Just as we press the release button the mirror moves up prior to the shutter curtain opening. The vibration caused by this mechanical move is accentuated by our long tele and the result is a photo lacking in sharpness. Using the mirror lock-up feature of the camera can result in improved sharpness. Different ways of using this feature are described by E. J. Peiker in his article “Advanced Long Lens Technique. Defeating the "Camera Shake" Enemy”. (15) 

If you are using support, use your body to stabilize your system - this is a tried and tested technique. Rest your free hand on your lens to keep it steady and push your head against the back of your camera (thus ‘jamming’ it between the lens and your face).  As with all techniques, practice makes perfect.

Using a rubber eye cap is recommended by a number of professionals; this acts as a shock absorber to minimize movements from the photographer’s head.

If at all possible, use the delayed release (timer) function of your camera with or without a remote control. This is only possible when your subject is static or very slowly moving – and again it requires the camera – lens combination to be mounted on a support system (preferably a tripod).

Finally, improve your shutter release technique. This is particularly important if the delayed release is not used. The recommended technique is to roll your finger unto the shutter release button instead of pushing down on it.  (16)

2.    Support

This becomes a critical issue with long teles. Even with good light levels, which means high shutter speeds allowing for a good number of lenses to be hand held, this is rarely feasible. The lens is heavy, the camera – lens combination is front loaded and needs steadying so that your hands will start shaking in less than a minute. Even the best image stabilization / vibration reduction system available cannot cope with hands that tremble.

The solution is to support the lens. This can be done using a tripod, monopod, beanbag or – for lack of the appropriate equipment – any steady surface that can be found around (we have often used a stone, rock or a thick branch of a tree. Even leaning against the trunk of a tree may help on certain occasions).

2a.  Tripods

Tripods are an extremely steady way of supporting your camera – lens combination. When using them make sure that the legs are properly extended and that all the knobs are fully tightened. If you need to leave some slack to ensure flexibility in following a moving subject make sure that the slack does not adversely affect the stability of your system. Professionals recommend trying to pull down on the tripod with your hand to make sure it is securely in place. Only then the lens – camera should be attached on it.

When selecting a tripod make sure it is sturdy enough to carry the weight of your camera + lens combination. Reputable manufacturers state the maximum load a tripod can take – take away 15% of that figure to be on the safe side or consider it as the absolute maximum and go for a bit extra. Alternatively you risk your expensive equipment which may gravitate towards the earth as the tripod loses balance or collapses under the combined weight.

Similarly, when selecting a tripod head, make sure it is easy to handle, sturdy enough to hold your lens without slippage and flexible. This is imperative to ensure effortless composition and accurate execution of the shot.

Adding some weight on the tripod itself greatly increases its stability. Do not extend the legs and the center column unless necessary. The shorter the legs the greater the stability. If you have a choice between hard and soft (but steady) ground, use the soft one, since it will act as a dampener and decrease camera shake.

Set up your tripod in a protected space, if at all possible; use a tree, shelter or even your body to shield your camera and lens from the wind.

Do not leave things dangling from your camera; straps and cables can cause vibration particularly during a windy day.

The advantage of using a tripod can be summed up in two words: sharper images. Depending on the weight and focal length of your tele a tripod may be a must. (17) The downsides of it are equally obvious:

  • Less flexibility in the field,
  • Carrying more weight (a sturdy tripod will add at least 4-5 kilograms to your field kit),
  • Added expense (carbon fiber tripods, which are lighter to carry, together with the appropriate ball heads and peripherals such as plates, grips etc will set you back at least the price of a good lens – think three digit numbers here).

If you plan to set up at a preferred location and wait for a subject to come in range, a good tripod is the ideal solution especially if the subject stays still or moves slowly. On the other hand, if you plan to walk around looking for a subject the combined weight of the tripod and the rest of your equipment will soon exhaust you.

2b.  Monopods

Monopods are a less expensive and more flexible alternative to tripods. However they do not offer anywhere near the support and stability a tripod does – and this can be a serious drawback with long heavy lenses particularly for amateur photographers.

2c.  Beanbags

Beanbags are used over other surfaces (or on the ground) to form a cushion over which the lens and camera are rested. Draped over a car window they form a platform which supports the lens when shooting from inside the car.  Over the years we have spent thousands of hours foraging areas looking for wildlife. We noticed that birds in particular are not afraid of moving cars but will fly away the minute the car stops and surely when a door is opened. We usually work as a pair - one drives very slowly while the other places the camera with the telephoto lens through the window opening (the beanbag comes in very handy to drape over the door part and stabilize the lens) and shoots. (18)

Used like this the beanbags are a good option, much safer and less threatening to wildlife than other methods such as setting a tripod in the car or shooting through the sunroof. (19)

2d.   Window and door mounts

Window and door mounts are also available; these accept a standard tripod head on which to secure your equipment. The issue with these mounts is that you have to drive with them in place or you need time to set up when you see the subject. This is usually a bad idea – by the time you are ready there is no subject to shoot. Driving with them in place is fine during the warm months but try it in cold or wet weather and you will soon start getting second thoughts.

If you are to invest either on a beanbag or on a mount bear in mind that the former is a much more flexible and easy to use tool in a variety of situations.

3.    Movement originating from the subject

The third kind of movement which can affect a photo originates from the subject. There is only one way to counteract this effectively and this is high shutter speed. High shutter speed is considered generally a must when using teles – the longer the tele the more it is required.  Note that even when you use high shutter speeds the use of a tripod may result in a better image.

You can achieve fast shutter speeds by opening your lens up (this is where fast teles come in handy) or increasing the ISO setting of your camera. Other things to consider are:

  • removing any filters that decrease the shutter speed (such as polarizers etc) unless you definitely need them
  • removing teleconverters if the light conditions are not favourable.

Lack of appropriate support in the field may result in limiting the use of a long tele in certain instances. Remember that the point is not to use a particular lens but to take a particular photo. In the following photo, the photographer had to walk inside a lake to shoot a pair of courting grebes. The bottom of the lake was a deep bed of mud, and therefore particularly unstable. Using support was not an option; the camera had to be handheld and she could only rely on the VR for image stabilization. Accordingly, though longer lenses were available, the lens of choice was the Nikkor 70-200mm f/2.8 VR.

4.   Other accessories

Long lenses can be used in a variety of situations: sports and wildlife photography are popular options amongst amateurs and professionals alike. If you plan to use your long lens outdoors you should consider the particularities of your shooting location and get prepared accordingly. Failing to do so may result in big disappointment as you may risk damage to your lens or not being able to use it in its full capacity.

A rain or splash protector is a must if you are shooting outdoors. Big teles in particular are bulky so your photography bag will most likely not be able to accommodate them if the weather gets suddenly wet. There are lots of different types available offering varying amount of resistance to water and dust. Get one that suits your needs and always carry it with you (it will not be much use tidily packed away at home while you are out in a T-shirt caught in a sudden summer shower with your new 300mm f/2.8). Rain protectors are also great by the beach to protect your camera and lens from sand or waves splashes.

You may need to shoot with the rain protector on so chose a type that allows easy access to the controls of the camera and lens while fully protecting both. Finally, choose an appropriate colour: a bright yellow rain protector may just defeat the point if you are trying to keep a low profile under the bushes in order to shoot that water fowl in the nearby stream.

Shooting wildlife may soon become a passion, in which case you may end up knee deep in a stream or lagoon with a considerably muddy bottom. A lot of photos taken at Strophylia Reserve, especially those showing eggs in birds’ nests, were taken with the photographer in the water till his waist. Wellies and waterproof overalls become a necessity; without them we would be simply unable to use the teles with any chance of getting some interesting photos.

If you are out shooting on your own and you enjoy the ‘active’ type of photography (i.e. moving around looking for a subject) you may want to consider a waterproof bag to carry your field kit.  Marshes are great places for wildlife but the ground is unpredictable and often gets flooded; protecting your expensive equipment from damage is of paramount importance. Consider that long teles are bulky and heavy so you cannot maneuver them as easily as shorter lenses; they are better off safely out of the way while you are exploring the ground or stumbling towards a good spot. There are various types of waterproof bags – including floating ones – available in the market. Choose one suitable for your needs but make sure it offers 100% protection for your equipment. Try it at home with something inexpensive but of equal weight to what you want to carry prior to taking it out to the field with you. If a bag is no good be inventive: we have often thought of inflatable kid floats ourselves!

Conclusions

Long lenses (teles) are attractive to a number of photographers; they are a must for certain types of photography. However they are neither cheap nor particularly versatile so they do require thought and planning prior to acquisition – and a lot of practice afterwards.

When choosing a lens try not to be impulsive. Get something which you will use and enjoy time and time again  – and most importantly – something that will allow you to be in control of the photos you take rather than something that will limit your ability to take photos by its many requirements.

Table of abbreviations for Nikon (Nikkor) lenses

This is presented in the images below:

 
      
 

Note: The numbers in parentheses in the table of abbreviations above correspond to the same numbers in the notes below.