Telephoto lenses by virtue of their large physical size are sort of “glamour” symbols of the photographic world. Just go to any photographic outing or clubs, those photographers with large telephoto lenses get the most envious glances. Telephoto lenses are indispensible for photographing sports and wildlife. They are also very useful for portraiture. While telephoto lenses (especially those with very long focal lengths) are difficult to handle physically due to their large size and weight, they are somewhat easier to use compositionally as they see a very narrow angle of view excluding a lot of unwanted surrounding elements. This makes composing easier.
Before we go deeper let us define what a telephoto lens is. It is a lens that provides a view narrower than that of a normal lens. Just as a recap, remember that a normal lens is the one that has a focal length approximately equal to the diagonal of the frame. Thus, for a full frame or a 35mm format it will be 43mm (though 50mm is more commonly used) and for the APS-C format it will be around 28mm. The angle of view (AOV) of such lenses will be around 46°. Here is a table that gives AOV for different focal lengths and formats.
The lens with the longest focal length ever produced for commercial use is the 2000mm f/11 reflex lens by Nikon. This is a manual focus length that weighs 17.5 Kgs! It is no longer in production. The longest autofocus lens that is being manufactured presently is the 800mm f/5.6 lens by Canon.
Fast telephoto lenses: As you may recall fast lenses have two advantages. They allow you to photograph at a lower light for the same shutter speed or use a faster shutter speed for the same light. Hence, fast lenses are very useful for low light and action (sports, wildlife, etc.) photography. As with everything in life there is no free lunch. Fast lenses are very heavy, especially at long focal lengths. The table below, which shows the weight of four 300mm lenses from the same manufacturer but with different speeds, illustrates this very well. You can see that an increase in one stop in speed has a drastic effect on weight. Price too increases rapidly with the f/2.8 version costing more than four times the f/4.0 version.
Handling telephoto lenses: You have seen that telephoto lenses, especially those which are fast and/or have long focal lengths are very heavy. Lifting or handling the lens plus camera combination with the camera alone without supporting the lens can damage the lens mount on the camera (by bending it or by misaligning it). Hence, once you mount a heavy lens you should always pick up and handle supporting the lens rather than the camera.
Mounting telephoto lenses on tripods: For heavy lenses, manufacturers provide a collar on the lens which has its own tripod socket to fasten the lens to a tripod head. If such a provision is there on your lens, then you must use it when mounting the camera plus lens on a tripod. If you fix the camera to the tripod head using the tripod socket on the camera then you can cause damage to the camera mount as explained. The tripod collar is designed so that the lens rotates within the collar. This allows portrait orientation without the need to flop (overhang) the camera to the side with a heavy lens mounted. This increases the stability of the setup considerably.
Tele-zooms and telephoto prime lenses: As the technology advanced, focal lengths which were once exclusive domain of prime lenses are now being catered to by tele-zooms. Not long ago zooms were limited to just 200mm. Now a days you can get many tele-zooms that go up to 400mm and there are even a few that go up to 500mm. The most popularly used tele-zooms are 55-200mm, 70-300mm and 100-400mm. Only where you need extreme speeds, focal lengths and highest quality does one needs to resort to primes. Examples of such prime lenses are 200mm f/2.0, 300mm f/2.8, 400mm f/2.8, 500mm f/4.0, 600mm f/4.0 and 800mm f/5.6. All of these are very expensive, large and heavy – actually very, very, heavy.
Acquiring the subject with telephoto lenses: Please refer to the table which gives the angle of view. From this you can see that when you mount a 300mm lens on a APS-C sensor D-SLR you will only see a very small area that corresponds to a AOV of just 5° 20’. Hence, you will have great difficulty in acquiring a moving target like a flying bird unless you have been tracking it from quite some distance. This problem gets compounded when you use even longer and heavier lenses. Also, a gimbal head will be very useful for subject tracking (more of it shortly). Needless to say practice also helps.
If you are using a zoom lens then it is better to start at the shortest focal length, acquire the subject and then zoom in to a longer focal length while keeping the subject under one of the AF area markers in the viewfinder. This is not very difficult but a little practice as with everything else in photography will help in getting you a larger number of keepers. There is one precaution that you need to take. You need to set your camera to continuous autofocus mode. This is the mode that will allow your camera to track and maintain focus as the subject moves. Also, many zoom lenses change focus (even when the subject is stationary) when the focal length changes. This aspect is taken care as well with continuous focusing.
Lenses with long focal length are difficult to hold steadily to their high magnification as any shake when the shutter is released will get magnified and will be visible prominently. In fact the single biggest reason for getting unsharp images when using telephoto lenses is due to the shake. So, how do you reduce this problem? Here are a few points that you should consider.
Use a Tripod: A tripod is an indispensable aid for any photographer regardless of the type of lens used. However, its usefulness is much more when you are using telephoto or super telephoto lenses. By using telephoto lenses on a tripod you will get a tremendous benefit. A tripod will keep the set up steady and will guarantee a sharp photograph. However, please remember that any tripod will not give you the results you want. At the minimum, to support a heavy telephoto lens you need a tripod with sufficient load capacity. It should be able to withstand the weight of the camera plus the lens and the head comfortably.
More important than simple load carrying capacity is the torsional rigidity of a tripod. This is basically the way a tripod resists rotation. Do this simple test. Mount a long lens (at least 300mm) on your tripod. Gently tap the side of the lens while looking through the viewfinder. See how much movement you can detect. Unless this is nil or negligible it simply means that the tripod does not have the torsional rigidity. Remember that longer the lens, higher should be the torsional rigidity. Good tripod manufacturers like Gitzo and Manfrotto specify the tripod models suitable for a range of focal lengths in their catalogs. Having a look at this will give you a good idea of this aspect.
Talking about heads, gimbal heads are best suited for heavy telephoto lenses as they offer unmatched tracking ease with little physical efforts. They are the best tools for photographing flying birds. However, they are specialized devices and are not useful for general purpose photography. Next best are high quality ball heads which can take heavy loads and are also flexible enough for tracking subjects though not to the same extent as the gimbal heads. They can be used for general purpose work too equally well.
Reduce the mirror vibration: The movement of the reflex mirror in a D-SLR can cause vibration reducing the sharpness. This vibration is most prominent at a certain range of shutter speeds. This range varies from camera to camera but is generally from ¼ to 1/15 sec. Try as much as possible to avoid this range of speeds by varying aperture and ISO.
If your camera has the mirror lock-up (MLU) feature use this as it will raise the mirror and keep it static when the shutter is released, thus greatly reducing the vibrations. Of course you will not able to see anything through the viewfinder once the mirror is raised (unless you are using Live View mode) so this is useful only for static subjects.
In case your camera does not have the MLU, you can use the Live View mode which will also raise the mirror and keep it there when the shutter is released. However, there is a small complication here, in case you are using Live View with auto-focus (AF) as some cameras offer two options.
One option achieves AF through the normal phase detection method and will involve mirror flipping up and down. Avoid this mode as it will involve mirror movement. The second option uses the contrast detection method to achieve AF. This uses the image sensor itself for AF. This is the one you should use since it does not involve any mirror movement once you enter Live View.
Last alternative is to use what is called the “Mirror pre-release” or “Exposure Delay” mode. In this mode, the mirror rises when you press the shutter release but the shutter will open only after a short delay (about a second). This delay will ensure that the mirror induced vibrations have died down before the shutter opens. Once again as you can expect this technique is useful only for static subjects.
Use a Monopod: A low cost but very popular device is the monopod. Using one will allow you to use shutter speeds up to 2 stops slower than the thumb rule shutter speed. These are easy to handle, compact and light. They are also a lot more flexible compared to tripods. If you are going to buy a monopod, pay particular attention to the head. Many make the mistake of attaching a normal ball head.
This is inconvenient in practice as the ball head allows movement in all directions making the set up difficult to handle. Instead of a ball head, buy a monopod head (like Model 234 from Manfrotto). This rotates only in one direction (pointing up or down) and is much easier to handle. These work best with those lenses which have a tripod collar as both landscape and portrait orientations are easily possible. If your lens does not have a collar, then you should use an L bracket. Panning is done by rotating the monopod itself.
So, how do you use a monopod? The best way to use a monopod is to use it like a tripod. Since a monopod has only one leg where do you get the other two legs from? Well, you can supply them J! Keep your two legs little apart and lean slightly on the monopod so that the monopod and your legs together form a tripod (see picture). This gives a good stable base.
Handholding of telephoto lenses: Not mounting a camera on a tripod or a monopod gives you a lot of flexibility (especially while tracking subjects that move rapidly like birds in flight or move randomly like a football player) but this does not guarantee sharp pictures unless the shutter speed is sufficiently fast. But how fast should it be? A very commonly used thumb rule is that you should use a shutter speed which is the reciprocal of the focal length or faster. That is, if you are using lens with a focal length of 500mm then you should use a shutter speed of a minimum of 1/500 sec. This was formulated during the days of 35mm film cameras. If you are using a full frame camera then the same rule will still hold good. If you are using a camera with an APS-C sensor then the minimum shutter speed should be 1/750 sec since a 500mm lens on such a camera will have a narrower angle of view due the cropping factor of 1.5. If you are using a 4/3 camera, the minimum shutter speed should be 1/1000 since the cropping factor is 2 in this case. As you can see getting such fast shutter speeds is not possible unless the light is very bright and/or the lens has a large aperture.
Fortunately, handholding received a tremendous fillip due to two technical advances. First is the excellent performance (that is superb quality images) of the new generation D-SLRs at very high ISOs. You can now get very good results at ISO values up to 3200 and even higher with full frame D-SLRs. Such high ISO values allow you to use high shutter speeds which were simply impossible when one was using film. The second advancement is the shake reduction technology that we will see shortly.
There is also a limitation that arises due to the weight of the lenses. This will depend on the physical ability of an individual and hence this will vary from person to person. In any case (unless you are also a weightlifter apart from being a photographer J) fatigue could set in after a while making your hands a bit unsteady and this will manifest itself as unsharp images.
During the last decade technologies that stabilize the image compensating against the hand shake have come into the market and it is not an exaggeration to say that these have brought in a major revolution in photography. These which go by commercial names like VR (vibration reduction), IS (image stabilization), OS (optical stabilization), etc., allow you photograph up to 4 stops of slower shutter speed than what your rule of thumb recommends! This feature thus gives a tremendous advantage when photographing in low light and/or long lenses.
Important: Remember that this technology compensates for your hand shake. It will do nothing to stop a moving subject! If you want to stop a moving subject like bird in flight, a racing car, etc., then you must use a fast shutter speed. There is simply no other way!
Portraits with telephoto lenses: Portraits are a favorite subject for almost everyone – from casual photographers to world famous professionals. When one is photographing a tight head portrait where the face occupies most of the frame, it is necessary to maintain a certain distance from the subject. If you ignore this and take such a portrait from a close distance, protruding features of a human (like nose, ears) can look abnormally large due to the exaggerated perspective that arises due to the short subject distance. So, you need to maintain a minimum distance from the subject to make the perspective more pleasing. Since you will move farther away and at the same time will need a frame filling image, you need to use a lens with a longer focal length. Short telephoto lenses with focal lengths from 85mm to 105mm (when you use a 35mm or a full frame D-SLR) are best suited for this purpose and are popularly known as “portrait” lenses. If you are using an APS-C sensor D-SLR the focal lengths of choice for portrait lenses are from 50mm to 85mm. Such lenses allow you a proper subject distance for a good perspective and at the same time allow certain intimacy with the subject as you will be reasonably close. You can also take portraits with a 600mm lens but then you will be yards away and unless you shout your instructions the subject will not be able to hear! This destroys the intimacy that was referred to.
Advantage of Cropped Sensors when using telephoto lenses: Cropped sensors (like APS-C and 4/3 sensor cameras) have a disadvantage as they cannot get most out of wide angle lenses as the angle of view reduces (narrows) by the crop factor. Thus, a wide angle lens will cover less of an area on a APS-C sensor camera than it would on a full frame camera. However, this same property will be useful when using a telephoto lens as now the reduced angle will be beneficial. Though not exactly the same, it is as if you have mounted a tele-converter of 1.5X when you mount a lens on an APS-C sensor camera. An added advantage is that there is no loss of lens speed as it would happen when you use a tele-converter. Just to recap, the focal length will not change. Only the angle of view will. So the next question is if this is so, why manufacturers can’t make cameras with very small sensors so as get a very narrow angle of view. Yes, this is being done in many bridge (prosumer) cameras but remember there are number of factors that inhibit this. First and the foremost is that as sensors become smaller the image quality will go down due to higher noise, poor low light performance and lesser dynamic range. Thus, it is not possible to make sensors very small and yet maintain high quality images. Present day cameras with APS-C sensors are an excellent compromise between these opposing needs giving the best of the both worlds.