Variable focus lens with ring and pin mechanism - is designed so that rings cannot be locked accidentally

The variable focus mechanism employs a slot in the lens barrel and a pin on the lens holder which engages in the slot. The pin is connected to a manually operated control ring, and a further control ring has a curved slot which moves the pin into an extension of the barrel slot for close-up focus adjustment when the first control ring is in a given position. In this position, which is defined by a stop, the pin is still in the barrel slot, and the second control ring has a dog which moves the pin into the barrel slot extension when this control ring is rotated.