Setting Lens Length on A5100 with 16-50 lens

[texxasal]

I have recently obtained an A5100 with the Sony 16-50 mm "E"  lens.

When I turn the camera on, the lens automatically goes to the 16 mm setting.

How can I set the camera, so that the lens automatically goes to, and maintains a setting of 20 mm?

I am using this camera in an application where manually zooming the lens is not possible after turning it on.

Thanks for any response, or pointing me in a direction where I can find this information

Al Rosenberg