Fast, long lenses necessarily require a lot of elements and big glass, so it's not surprising that this one is pretty big for Micro Four Thirds.
That front section is the manual focus cuff. When you pull it back, you're in manual-focus mode, when extended, it autofocuses.
The lens has a focus-limiter switch with three choices: 1.4-4m, 1.4m to infinity (the entire range), and 4m to infinity. There's also a programmable function button and stabilizer toggle.
If you need more reach, Olympus' 1.4x teleconverter can increase the effective focal length to 420mm (a 35mm- equivalent angle of view to 840mm) and 0.67x magnification.
Part of the lens' size is a result of the necessary distance between lens elements.
The dot-sight accessory mounts next to the camera and aids you in keeping the subject in-frame with minimal head movement.
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