Borescope

Rod lens are extensively used in borescopes. But to get a better understanding of rod lens, one must have an idea of their exact role in terms of producing the image that the viewer sees at the eyepiece of the borescope.

As you probably know, borescopes are either rigid or flexible. The difference between rigid and flexible borescopes is in the construction. Most rigid scopes incorporate a convex glass lens system, in which the small glass lenses are separated by large air spaces. Basically, those individual lenses magnify the image and present it to the eye for viewing. A flexible borescope uses a coherent fiber bundle with thousands of individual fibers to relay the image from the objective to the eyepiece. Due to this technology, the image from a fiberscope is never as good as a rigid one with the same diameter. What’s more, the focus ability of a flexible borescope is greatly reduced.

In contrast, the rod lens telescope, invented by Professor Hopkins, utilizes comparatively longer rods of glass and smaller air spaces. The main advantages of the rod lens system are the greater light transmission, better image resolution, wider field of view and image magnification.

Currently, the small-diameter rigid endoscopes usually utilize the Hopkins rod-lens relay system because it offers much better aberrational correction and light throughput than the traditional form of relay system. However, there are disadvantages to that system as it does produce a significant amount of astigmatism and field curvature which may reduce the off-axis image quality appreciably. The rod-lens employed in the Hopkins system consists of a singlet field lens and a doublet aperture lens which are both cemented onto a cylindrical rod.

Rod Lenses are polished on the circumference and ground on both ends. Their optical performance is similar to a cylinder lens. Collimated light passing through the diameter of the rod will be focused into a line. All dimensions are in mm.

Other advantages of rod lenses are that they provide uniform ultraviolet curing of large areas and eliminate distortion and movement in optical applications, such as casting lenses and domes and positioning of fiber optic components.

Rod Lenses are generally used as light pipes. Its optical principle is similar to fiber optics where light can be transmitted from one end to the other with relatively small leakage. Rod Lenses can also be used as cylindrical Lenses. In certain application, Rod Lenses can also be used as homogenizers.

Upper Endoscopy | Borescope Lens | Camera Lens | Gradient Lens | Optical Lens | Rod Lens |