Teleconverter / Extender

What is a teleconverter / extender?

A teleconverter / extender is a second lens that is placed between the body and the main lens. This is done in order to increase the focal length of the main lens and to be able to see objects that are further away. With a 2.0x teleconverter, the focal length is doubled, so for a 70mm lens it would become 140mm. The teleconverters and extenders available from brands such as Canon, Sigma, Kenko and Nikon all state which type of lens they are suitable for. A teleconverter is specifically designed for focal lengths from 50mm to 300mm, at a smaller (wide angle) or larger (macro) distance there is too much loss of quality.

Advantages of a teleconverter / extender

The biggest advantage of a teleconverter is that the focal length of a lens can be increased at an affordable price. Lenses with a long focal length are often unaffordable for the average consumer, especially for more expensive brands, but a teleconverter makes it possible to go from 300mm to 600mm, for example. Another plus is that with an extender, the central part of the image is enlarged, making any dark corners disappear.

Disadvantages of a teleconverter / extender

A disadvantage of using a teleconverter is that it decreases brightness and sharpness, as the extender has a higher magnification factor. With a 1.4x converter this is one stop brightness and two stops with a 2.0x. With a 300mm f / 2.8 telephoto lens, the use of an extender turns the lens into a 600mm f / 5.6 telephoto lens, which immediately shows the reduced brightness. In addition, image errors are further enlarged by the converter and are therefore more visible in the image. When using the autofocus function, the speed increases with the larger teleconverters and it is therefore important to consider which lens the teleconverter can work well with.

Operation in the dark

Due to the reduced brightness when using a teleconverter, it is advisable to work with a faster shutter speed when using this intermediate piece in the dark. However, this also has an effect on the final recording, as noise and reduced sharpness will be noticeable in the end result. This makes the teleconverter particularly suitable for use during daylight, as the best results can be achieved at these times.

Communication between lens and camera

A great deal of progress has been made in the development of teleconverters / extenders with regard to data processing between the lens and camera. This improves the performance when using the autofocus function and offers tighter communication with light metering and image stabilisation functions.