assembly. Take care to keep lubricant from the friction disc and the locking surfaces. Lubricate the yoke assembly by removing the binocular and removing the three screws and lift dial support; then lift the yoke from the carriage post and lightly coat the interior bearing surface of the yoke. CAUTION Two persons should be used to lift either the binocular or yoke assembly. BINOCULARS Binoculars (fig. 2-15) are the most commonly used of all optical equipment. Although normally only 7-power, they give a wide range of vision and are best suited for searching over a wide area or for following moving targets. They require the use of both eyes and, because both eyes do not always have the same vision, it is better to adjust the focus for each lens individually. Proper focus is essential. If the focus is off, eyestrain is increased greatly, and you will not get maximum efficiency  from  your  optics. To obtain the proper focus for each eye, turn both binocular scales to the +4 setting. Hold the binoculars firmly against your eyebrows. To get the focus for your left eye (only one eye can be focused at a time), cup the right hand over the right lens, cutting all light to that eye. Be sure to keep both eyes open, however, because closing one eye will give an incorrect focus. Train the binocular on a small well-defined object. Figure 2-15.—7 × 50 binoculars. Slowly turn the eyepiece from the +4 setting until the object stands out in sharp detail. The reading on the scale gives you the correct focus for your left eye. Now do the same for your right eye. The chances are the setting will be different. Repeat this step several times to make sure the focuses are  correct. Once  you  get  the  glasses  focused  properly, remember  your  settings  so  you  can  focus  your binoculars on a very dark night. The correct night focus usually is a -1 setting from your day focus for each eye. The other adjustment for binoculars is the IPD adjustment. All Navy binoculars have the IPD scale on the hinges between the barrels. Find out what your IPD is and remember it. It may already be in your health record. If not, have a medical officer measure you for it. When you have set your correct IPD scale, you will see a complete circle, never overlapping circles. At night, if you have the wrong IPD setting, you will cut out a lot of light that should be going to your eyes. Take  a  look  through  a  pair  of  binoculars  not adjusted for your eyes, then look through a pair that is adjusted properly. Notice the difference. If possible, always use the same binoculars. Most  glasses  are  treated  scientifically  to  reduce glare, but there are times when the direct rays of the sun  are  so  strong  that  it  is  almost  impossible  to distinguish  shapes  and  colors.  To  overcome  this handicap, glasses usually have colored lens filters that can be inserted over the regular lenses, reducing glare considerably. CARE OF OPTICS Optical   instruments   require   great   skill   and precision in their manufacture. They are both delicate and  expensive.  As  with  all  precision  equipment, careless handling can render them out of adjustment or useless. All maintenance should be accomplished according to current MRCs. Your optics have many enemies. The major ones are dust, heat, light, and moisture. A severe shock, such as falling to the deck, may cause breakage either of lenses and prisms or mechanical parts. A sharp shock invariably causes the prisms and reticles to become  misaligned. 2-13