Teleconverters, Wildlife photographer's tool
Teleconverters, Wildlife photographer's tool | ||
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Teleconverters (or extenders) are optical devices that fit between the lens and the camera body, and magnify the image from the lens by a specific amount. They are most often used by wildlife photographers, requiring longer focal length lenses, but they do have a use in close-up and macro photography: They increase the focal length and thereby increase the working distance to the subject. They are available in various strengths: 1.4×, 1.7×, 2×, and 3×. A 300 mm lens, attached to a 1.4× converter, becomes effectively a 420 mm focal length, while a 200 mm lens attached to a 2× converter becomes effectively a 400 mm focal length. I often use a 1.4× converter with my 105 mm f/2.8 Micro-Nikkor VR lens, giving a combination of 150 mm f/4. This increases the working distance for a given magnification and increases the maximum magnification to 1.4×. The amount of light reaching the sensor is reduced by the converter. A 1.4× converter reduces the amount of light by one stop, and a 2× converter reduces the amount of light by two stops. Thus, a 300 mm f/4 lens, when used with a 1.4× converter, becomes effectively a 420 mm f/5.6 lens. It is well worth buying the converter from the same manufacturer as the lens with which you will use it since converters are very often matched to specific lenses. Cheaper models are available, but may give poor results. As discussed earlier, increasing the focal length of the lens increases the working distance from camera to subject. For close-up and macro work, however, it is possible that the lens/converter combination will not focus close enough to the subject and there will be the need to use extension tubes (or close-up supplementary lenses) to achieve the required magnification. There are two ways of doing this. You can either place the extension tube behind the combined lens and converter, or you can put the extension tube behind the lens, then the converter behind that. Using the example of a 105 mm lens with a 1.4× converter and extension tube:
Take great care when experimenting with combinations like this, and read the manufacturers’ instruction manuals carefully. Some extension tubes cannot be used with, or don't physically fit, some lenses or converters, and may damage the delicate linkages if forced into position. When using this type of combination, check the corners of the image carefully for vignetting, which may result with increasing magnification. | ||