Teleconverters or Extenders are attachments placed between the camera and lens that increase the focal length of the lens by a given factor. A 1.4x teleconverter will give a focal length of 280mm if used with a 200mm lens; a 2x would make it a 400mm lens. The cost of high quality fast lens seems to increase exponentially with focal length (the Canon 800mm ƒ/5.6 IS USM lens costs $13-14,000) so teleconverters offer a much more affordable way to reach these focal lengths.

However, there is a catch: attaching a teleconverter will reduce the maximum aperture of your lens. A 1.4x teleconverter will reduce it by one stop (so an ƒ/2.8 becomes an ƒ/4); and a 2x will reduce it by two stops (an ƒ/2.8 becomes and ƒ/5.6). This means that you’re going to need a fast lens. The issue is not just longer exposure times and a loss of depth of field. The camera’s autofocus system will also require a sufficiently large enough aperture to work effectively.

If you’re starting with an ƒ/4 lens and using a 2x teleconverter, you’re now at ƒ/8 at which point most autofocus systems will not work and you’ll need to focus manually. Consequently, to use a 2x teleconverter you ideally need to have an ƒ/2.8 lens; for a 1.4x you could start with an ƒ/4 lens—at ƒ/5.6 autofocus will still work but the number and type of AF points will be reduced.

You May Also Like

Metering Modes

There can be up to four metering settings in DSLRs: Evaluative, Centre-Weighted, Partial, and Spot. Below are the…

Back Button Focus: Why You Should Be Using it

Many cameras these days give you the option to reprogram some of the buttons in the custom function…

Mirror Lock-up

Mirror lock up is feature on most higher end DLSRs to reduce (minor) vibrations produced when the mirror…

Megapixels: Why More is Not Always Better

Walk through the camera department of any electronic seller and the first statistic you will see next to…