A pair of binoculars is considered a double telescope, handheld device.
Binoculars magnify the image you’re viewing by collecting the light rays from the object. The light will then enter the objective lens and an image will be projected behind the lenses. The image will be magnified but it will be upside down at this point because the objective lenses are curved. To correct it, each lens will require a glass prism.
Workers use UV light-activated glue to mount the prisms on the steel plates. The steel plates then grind and polish the prisms. They are also painted with protective paint to keep dust away from the pristine surface. Next, they are ground with diamond dust which eliminates tenths of a millimeter of glass. The prisms will be polished after using a finer abrasive. This will remove another 1/100 of a millimeter. The three sides of the prism will then be flawlessly flat. It’s important that they are flat to reduce reflection, which is critical for making the glass transparent. In order to make a prism, the workers glue two pieces of glass together at 90 degrees. A special machine is used to make sure the angle is precise.
Next, the glue will be dried with a shot of UV light. The first piece of glass flips the inverted image 90 degrees, the second one flips it another 90 degrees, making the image rotation complete.
These lenses are curved and undergo the same grinding and polishing as that of the prisms. However, they experience a nine-stage, computer-guided cleaning process. This happens after a technician carefully and perfectly glues together two lenses. Doing this will limit the kind of distortion that causes fringes of color to appear near the image. If the alignment is off by more than just one-hundredths of a millimeter, the image will have a poor quality. To ensure the alignment won’t be off, the technician uses an alignment machine which displays a dot that represents the center of each lens. The technician just has to make sure the dots are matched.
UV light will then be shot again for two seconds in order to dry the glue. Afterward, a vacuum chamber will be loaded with mineral pellets. This is done by another technician. Note that the exact formula for this step is a company secret. Next, the pellets will produce an anti-reflection lens coating which allows more light to pass through the lenses. A beam of electrons will then evaporate the pellets inside the vacuum chamber. Once the pellets become microscopic particles that coat the lenses, the assembly of binoculars will then begin.
The housing can either be made of aluminum, plastic, or carbon.
The objective lenses are attached to the housing first then the workers ensure the lenses are clean by giving them a few puffs of compressed nitrogen. Using threaded holding rings, the workers secure the lenses carefully. The worker will then place a few drops of glue behind the objective lens where the prisms will be positioned. Once again, a puff of compressed nitrogen will be let out to remove any dust. The prisms will then be inserted with the help of an optical machine which aligns the focal points of the prism and its matching objective lens. Glue will once again be used to lock their positions and a shot of UV light will be blasted again to dry the glue. This is where silicon enters the picture. It is used to create an airtight and waterproof seal that will keep the objective lenses and the prisms in the housing. A holding mechanism then presses the parts together as the workers drive the screws in. Now one end of the binoculars is done!
The oculars are first placed on the other end of the middle section. The oculars are the smaller lenses where we peer through. They are also secured with threaded holding rings. Then, through a valve on both sides, a machine will suck air from the housing and blow nitrogen gas. Nitrogen will prevent the lenses from fogging up. After one day, the workers will check the nitrogen pressure and ensure that there’s no sign of a leak.
Some companies let their binoculars undergo rigorous testing, exposing them to water pressure, prolonged vibration, extreme heat, freezing temperatures, and other conditions. The binoculars will then be checked to know whether or not they’re still working perfectly like they should.