When you slide the lens back towards the body, it is shrinks. The lens remains at the length you slide it to by friction. You can slide it back and forth while the light is on or off. Its a bright flashlight. On the end, you find the metal power switch which is located in the end cap of the flashlight. It’s a spring loaded click switch with good tactile feedback. It has a three switch function, press power without clicking it for maximum light, click it once for low light, click again for high beam and then again to power it off.