Specialists who are interested in rigid borescopes want to know their pros and cons.
A rigid borescope is an optical instrument with a metal insertion probe and eyepiece on one end and an objective lens on the other. There is a complex relay optical system between them. There are three types of optical systems: Hopkins rod lenses, achromatic doublets and gradient rod lenses. For large diameter the achromatic doublet relays are sometimes used. For smaller diameters the rod lenses provide better images. For very small rigid borescopes, the gradient index lens relays are better. The insertion tube also contains glass fibers for illumination. The illumination can be provided either by LED light source attached as a handle to the light post of the borescope, or by an external powerful Metal Halide, LED or Halogen light source. In the latter case the light is transmitted through flexible glass fiber guide. An internal image of the object is formed by the objective lens and magnified by the eyepiece, which presents it to the eye.
What are advantages of rigid borescopes? They provide a superior image at lower cost compared to fiberscopes. The image has a very high clarity. When an object is located within direct access, rigid borescopes work well. They are recommended for gunsmithing, automobile inspection like observation of automotive cylinders, injectors and hydraulic manifold bodies. A video camera can be attached with the help of special adapter to the eyepiece, and after that it is possible to record video and still images for further processing.
What are disadvantages of rigid borescopes then? They are limited to access to a straight line. It is impossible to view hidden objects behind obstacles. Besides they are fragile instruments and don’t like falling down.
There are many rigid borescopes in the market with diameter from 1.8 mm to 8 mm and length from 10 cm to 90 cm. As you can see they have more advantages than disadvantages and can be very efficient for inspection work.