Extenders

Extenders, also called tele converters, are devices which magnify the center part of what lens is seeing and therefore they multiply the focal length. When center part of lens is multiplied some light is also lost and therefore 1.4x extender makes lens one stop dimmer and 2.0x extender makes lens 2 stop dimmer.

Example: Lens which focal length is 200mm and maximum aperture is f/2.8 is used with 1.4x extender it becomes 200mm x 1.4 = 280mm and the maximum aperture is one stop dimmer, which in this case is f/4 lens.

Canon EF 1.4x II

Optical performance

Handling and usage

Compatibility

Generally all telephoto primes longer than 135mm, except soft focus 135mm, are compatible. From zoom lenses 70-200 and longer lenses are compatible. Also TS-E lenses are compatible even Canon doesn't mention it. However take into account that if you add 1.4x to f/5.6 lens the autofocus will not work on non-professional Canon digital SLRs.

Summary

Pros:
+ 40% longer focal length
+ Pretty small impact to image quality
Cons:
+ Image quality is slightly decreased
+ Autofocus slows down and hunts easily
+ Protruding lens elements cause compatibility issues

Kenko MC 7

Optical performance

Handling and usage

There isn't anything specific regarding handling. It attaches to lenses and cameras as well as you could thing. There are no adjustments etc.

Usage is as with any other extender except that this extender will not show true aperture on the camera's displays or in the EXIF data. Focusing performance is naturally much worse than without extender.

Compatibility

This extender does not have any protruding parts so it's compatibel with all Canon EOS lenses. However take into account the limitations to autofocus.

Summary

Pros:
+ 100% longer focal length
+ Physically compatible with all Canon EOS lenses
Cons:
+ Image quality is decreased
+ Autofocus performances

Pictures of extenders

Canon EF 1.4x Mark II

As you can see from photo there is lens group which protrudes inside the tele lens the extender is attached to.

Kenko MC 7

On Kenko extender there are no protruding parts and physically compatible with all Canon EF lenses.