If you need to visually inspect a small, restricted area — one that you cannot easily gain access to — you can use an instrument called a borescope. This is an instrument that has an optical lens on one end (sometimes also with a light-shining device) and an eyepiece or some other attachment on the other hand for viewing. Many borescopes are of the “rigid” variety — the tube in which it is encased is not capable of bending. These rigid borescopes cannot, however, be used in situations where you need to see around a bend. In these situations you need a borescope that is flexible — and fiber optic borescopes will fit the bill quite nicely.
Fiber optic borescopes — like all borescopes — can be used to view areas that are extremely small, or restricted — and because they must be used in restricted areas, they are often equipped with a wide angle lens to expand the field of viewing as much as possible. In addition, one or more of the fiber optic cables can also be made to transmit a small amount of light to the end of the fiber optic borescope, which shines out of the end to light up the area so it can be seen better.
Because the amount of available light is very limited, and due to the use of the wide angle lens, the image seen through a fiber optic borescope may be somewhat less than perfect; nevertheless fiber optic borescopes are used in everything from building inspections, to automotive repair, computer repair — even in medicine (a fiber optic borescope used for inspecting interior parts of the body is called an endoscope). Because the optical images are transmitted through the fiber optic cables, fiber optic borescopes are capable of transmitting an image over a long distance: some fiber optic borescopes are manufactured in lengths reaching hundreds of feet!
What criteria should you use when evaluating a fiber optic borescope? Well, obviously, the most important aspect is the quality of the viewed image. After all, the point of using a fiber optic borescope is to be able to see something clearly — so a fiber optic borescope with very poor image quality is of no value.
Another characteristic of good-quality flexible optic borescopes is their degree of flexibility. What I mean by that is: how far, and in what directions, can you move the flexible end, when you are inside something looking around? You want to choose a fiber optic borescope that provides you with the greatest range of movement.
In addition, you want to purchase a fiber optic borescope that provides you with a full field of view with as little optical distortion as possible. One commonly used specification is the number of pixels — a minimum of 10,000-12,000, and if possible 15,000-20,000+ should be provided by a good-quality fiber optic borescope. The better ones provide a higher number of fiber optic filaments.