Key features

• Dust and moisture resistant
• Extends the lens focal length by 2x
• Very high quality optics to maximise lens performance
• Integrated processor to transfer all lens and focusing information
• Internal baffles to reduce inner reflections for higher image quality

To ensure lens optical performance and autofocus performance remains high, both extenders feature an integrated processor to transfer all focus and lens information back to the camera. To ensure this is working optimally, you should always attach the lens to the extender before attaching the extender to the camera body. This will ensure the combination lens information is transmitted correctly and completely. Compared to the Mark II Extenders, these new Mark III Extenders will offer increased AF performance with all EF lenses.

The extenders are compatible with any L-series lens with a focal length of 135mm or longer, as well as the following zoom lenses: the EF70-200mm f/2.8L IS II USM; EF70-200mm f/2.8L IS USM; EF70-200mm f/2.8L USM; EF70-200mm f/4L IS USM; and the EF70-200mm f/4L USM.

For wildlife and sports photographers these extenders can prove invaluable accessories – the lion that is too small in the frame with the EF400mm f/2.L IS II USM lens gains much more impact when the EF1.4x III is used to give a 560mm f/4 lens. Using the EF1.4x III will cause a loss of one stop of light, so a lens with an f/2.8 maximum aperture will become an f/4 maximum aperture. The EF2x III Extender causes a loss of two stops of light, so an f/2.8 lens becomes an f/5.6 lens.

Both of the extenders feature dust and moisture resistance, so when they're used with their compatible lenses you can continue shooting in severe conditions. The join between the extender and lens and camera body has also been made tighter. This makes the unit feel more firmly attached and helps to minimise dust and water ingress. The lens mount also features more screws to provide a more robust mounting point.

The design has been modified to fit the look of the EF300mm f/2.8L IS II USM and EF400mm f/2.8L IS II USM lenses and the lens release switch has been changed to allow quicker attachment and release of the extenders. This is especially useful in harsh environments where minimising the time that the lens is off the camera helps to keep dust and moisture out of the camera body.

If the lens features an Image Stabilizer this will continue to function when the extenders are fitted. Similarly, with an EOS-1 series camera, autofocus will continue to function on all lenses when using the EF1.4x III extender. Using the EF2x III extender will cause autofocus to stop working if the maximum aperture falls below f/8. With non-EOS-1 series cameras this limit is reduced to f/5.6.

• Internal reflection coatings

The EF Extenders featured high levels of internal reflection baffling to stop stray light bouncing around within the extender body and thereby affecting image quality.

• Weather sealing

Both extenders feature dust and weather sealing to maintain the high levels of weather sealing provided by the Canon L-series lenses and the EOS-1 series cameras. You can use them in adverse conditions without worrying that they will introduce a weakness to the system.

• Fluorine lens coating

In the quest to keep the lens elements clean and thereby realise the best image quality possible, the front and rear lens elements have been coated with Fluorine. Fluorine is a non-stick coating that helps repel dust and water, and makes the elements easier to clean should any dirt find its way there from rain drops or fingerprints.