Focus gears allow access to the mechanical zoom function of many lenses. Use of these gears may require specific port extensions and may not be available for all housings and lenses.
This focus gear is specific for the Sony SEL1635Z Vario-Tessar T* FE 16-35mm F4 ZA OSS lens.
To install the Focus Gear along with the Zoom Gear it is essential to properly place the plastic insert on the lens. To do this you need to install the zoom gear plastic liner from the bottom of the lens with the lip of the plastic insert facing towards the top of the lens.
Then you will need to install the rest of the Zoom gear from the bottom of the lens and and then hook the plastic insert of the focus gear over the top plastic lip that emerges from beneath the metal zoom gear
Then you will be able to install the focus gear by sliding the metal portion over the top of the lens and pressing it down until it sits flush with the plastic insert.