Working with extenders
Get frame-filling shots with the help of these accessories
Teleconverters – or ‘extenders’ as Canon calls them – give you even more pulling power. These accessories can be fitted between the camera and a compatible lens to increase the focal length. Canon offer 1.4x and 2x extenders in both EF and RF mount fittings. The 1.4x extender increases the focal length by 40 per cent – so a 400mm lens gives you a focal length of 560mm. It costs one stop of light though, so the maximum aperture will be one stop slower (a 400mm f/5.6 lens effectively becoming a 560mm f/8 lens with the extender in place).
A 2x extender increases the focal length by 100 per cent, but costs two stops of light. You may also notice more of a decrease in image quality compared with a 1.4x extender.
The loss of light does have implications for exposure (as shutter speeds won’t be as fast – unless you increase the ISO to compensate). It can also affect the autofocus, although this will depend on the camera. Beginner-friendly DSLRS such as the EOS 4000D will offer only autofocus in the viewfinder when the maximum aperture is f/5.6. This means that you’d need to be using a lens that has a maximum aperture of f/4 or faster to use autofocus with a 1.4x extender attached (due to the one stop loss of light). If you want to attach a 2x extender, you’d need to be using a fast pro lens with a maximum aperture no slower than f/2.8.
More advanced DSLRS have one or more AF points that work down to f/8, but the mirrorless EOS R System cameras can continue to focus with even smaller apertures. Take the EOS R7, for example, which continues to autofocus when the maximum aperture is as small as f/22.