eye. Each eyepiece is adjustable through a range of +2 to -6. Each objective lens assembly is focused by rotating the focus knob. The objective lens is screwed into the mounting collar and the knob is attached to the lens and held in place by the focus knob retainer. Rotating the focus knob positions the objective lens for viewing at desired ranges. The eye relief adjustment allows the binocular assembly to be moved within the frame for eye relief and comfort. Clamp knobs, located on either side, can be loosened by turning the knobs counterclockwise and manually moving the frame to reposition the binocular assembly with reference to the user's eyes. The assembly is tightened into place by turning the clamp knob clockwise. Operation The principles of operation are the same for the AN/PVS 5A, 5B, and 5C. The operating phase of night vision goggles consists of pre-operation, test operation, and post-operation instructions. Pre-operation instructions: 1. Release the air pressure as instructed on the side of the storage case. 2. Release the latches and open the storage case and remove the goggles. Inspect the goggles for damage. 3. Ensure the rotary switch is in the OFF position. 4. Use only one battery compartment at a time. Insert battery/batteries (AN/PVS 5A uses only one lithium battery; the AN/PVS 5B and 5C use either one lithium battery or two alkaline batteries in one compartment) and replace the cap. 5. Snap the headstrap to the face mask, making sure all straps are extended to their maximum lengths. Place the head strap on your head, grasp the straps with both hands and slowly pull until the face mask cushion touches your face. Continue pulling until the goggles feel snug. Perform the same step for the vertical head strap. 6.    Remove the objective and eyepiece lens caps. If demisting shields are used, snap them over the eyepiece lens. Be careful not to smudge the eyepiece lens or demisting shield. 7. Loosen the lever clamp and adjust the monoculars for proper distance between your eyes. Tighten the clamps. 8. Loosen the clamp knob and adjust the binocular assembly until the eyepieces are located a comfortable distance from your eyes with proper tilt. Tighten both clamps. Instructions for test operation: 1. Position the rotary switch to the ON position. 2. Loosen the lever clamp and adjust the goggles for proper spacing between the monocular eyepieces. Retighten the clamp. 3. Loosen both clamp knobs and adjust the goggles for proper tilt and eye relief. Retighten the clamp knobs. 4. On the AN/PVS 5A and 5B, turn the focus knob fully counterclockwise on each objective lens for distant viewing. Adjust for the clearest view. The focus knob may be turned fully clockwise to adjust for a minimum focus of 10 inches. On the AN/PVS 5C goggles, the focus function is part of the objective lens assembly. To focus the goggles for the sharpest view, grasp the outside of each objective lens assembly and turn it to obtain the sharpest image. 5. Adjust each diopter ring until the image is sharp (the diopter ring adjusts the diopter for each individual user and does not require movement after initially set). 6. Pull and turn the rotary switch for IR operation (optional test). Return the switch to ON for normal operation. The rotary switch turns the goggles and IR illuminator on and off. Be sure it is turned to OFF when the goggles are not in use. Post-operation instruction: 1. Remove the demisting shields, if installed, by grasping them and pulling them off the eyepiece lenses. Return them to their case. 2. Replace the objective and the eyepiece lens cap. 3. Ensure the rotary switch is in its OFF position. Remove the battery (or batteries) from the battery compartment(s) and return it to its case. Replace the battery caps. 4. Inspect the face mask cushion for tears, cracks, or missing snaps; also inspect the goggles for missing parts. 5. Clean the goggles, carrying case, and shipping case as necessary with fresh water. Ensure both cases and liner are dry prior to storing the goggles in them. 2-18