They are constructed with metal bayonets, and engineered plastic ends. There are no moving parts, other than the lens latch lock. Two generations of the extenders exist, the older 1.4× and 2×, plus the newer 1.4× II as well as 2× II. The newer II versions have weather-sealing and anti-reflective surfaces inside the extender body. The optical construction of the 1.4× versions are a of five-element design. Both 2× versions use seven elements, although the optical formula of the II version is different, to improve optical performance
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