Whatever kind of photography you’re into, there will likely come a time when you want to get closer to your subject using a longer telephoto lens. But do you buy another lens for your kit bag or an extender?
Extenders or teleconverters fit between your SLR camera body and the lens and increase the focal length typically by 1.4x or 2x. So 200mm becomes 280mm (1.4x) or 400mm (2x), 300mm becomes 420mm or 600mm and so on.
Teleconverters are specific to the camera system being used, as they must have the correct lens mount for the system in use, i.e. a Nikon extender cannot be used on a Canon body and vice versa. Third party manufacturers, such as Sigma, offer models for various camera systems, so do check you’re buying the right one.
Pros and Cons
Like everything in life there are upsides and downsides to using teleconverters rather than a dedicated long lens. Things to consider:
|Cost||Adding a teleconverter is typically way less expensive than buying another lens, especially when you get to the 400mm territory.|
|Weight||Even the combined weight of a teleconverter and lens will be less than the weight of an equivalent dedicated lens – just think of the sports photographers at football matches, tennis or motorsport!|
|Maximum aperture||Adding a 1.4x teleconverter will reduce the maximum aperture of your lens by 1 stop, e.g. f2.8 becomes f4. A 2x loses 2 stops, so that f2.8 becomes f5.6.|
|Speed of focusing||A dedicated prime or zoom long lens will perform better when focussing than a lens combined with a teleconveter, so if very fast, accurate focus is critical, maybe a teleconverter isn’t for you.|
|Minimum focus distance||With a teleconverter, your lens keeps its minimum focus distance, quite useful perhaps as an alternative to a dedicated macro lens.|
|Image quality||Although extenders have improved over the years, you’re still adding extra glass to your setup and that means more image degradation, but it may still be acceptable.|
One other critical factor to look out for is whether a camera body/lens/teleconverter combination will still be able to use auto-focus. For example, if your camera needs f5.6 to use autofocus, then adding a 2x converter to say an f4 maximum aperture lens, means you’ll be forced into using manual focus, why? Well that f4 lens, with a 2x becomes an f8 maximum aperture (you lose 2 stops with a 2x and 1 stop with 1.4x). This reduces the amount of light entering the camera and with an f5.6 needed for auto-focus, you’re stuck with manual focus.
Some cameras allow auto-focus at f8, e.g. Canon’s EOS 1DX and 5D MkIII, so the combo above will work. Alternatively, an f2.8 lens plus 2x, which results in f5.6 max aperture, would be able to use autofocus.
Make sure you know what your camera/lens/extender combo would do before you buy!