With a focal increaser, the effective opening of the lens is reduced by 1 or 2 value (s) depending on the model used. The autofocus no longer works if this resulting opening becomes smaller than F/5.6 (smaller than F/8 with an EOS 1V and an EOS 3).

The EF 2x II doubles the focal length of the objective on which it has mounted and reduces its effective opening of two notches

The new version II of the EF 2X multiplier cannon retains the remarkable optical functions of the previous version and incorporates a waterproof case and a barrel with improved anti-reflective surfaces.

The Canon EF 2x II multiplier provides improvements to produce a very high quality image. This multiplier allows you to benefit from a practical and effective solution to double the focal length of objectives, with a loss of image quality and minimal performance. Its tightness of dust and humidity is in accordance with the endurance of all new boxes and objectives of the EOS system. Specifically designed for use with the EOS-1V and the super telephotal is Series L, this multiplier preserves their sealing.
The EF 2x II benefits from an optimized optical formula in terms of correction of internal reflections and multilayer treatment of lenses on the edge of the field. All of its optimizations allow photographers to obtain still superior quality images.

Compatibility:
Extending is the Canon appellation for a focal increaser. This high performance accessory multiplies the real focal length of the objective by 2. For example, a 200 mm objective associated with a 2x extender has a real focal length of 400 mm. This extender is compatible only with certain EF objectives.

Standing dust and humidity construction
Focal multiplication by 2x
Loss of performance and minimal image quality
Maximum reduction in internal reflections for optimal image quality