Auto-focus night vision device

A night vision device comprising:

• a housing having a first end and a second send;
• an objective lens mounted on the housing nearer to a first end than a second end, and arranged for receiving light from ambient into the housing;
• an image intensifier mounted on the housing and located toward the second end of the housing from the objective lens;
• an eyepiece lens mounted on the housing and located toward the second end of the housing from the image intensifier;
• an adjustable iris defining an iris opening, the adjustable iris being mounted on the housing and located toward the second end of the housing from the objective lens;
• a sensor for detecting light intensity connected to the housing and located toward the second end of the housing, the sensor being configured to control a size of an area of the iris opening in response to the light intensity detected for keeping the area of the iris small so as to maintain a depth of field of the night vision device.