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How Does a Borescope Work?

Last Updated: 06.12.21


If you want to buy a borescope for iPhone, you should know that there are many models available on the market. With a little research on your part, you can find anything you need to know about these devices. Borescopes are actually very helpful tools and are used in multiple domains of activity.



What is a borescope?

A borescope is an optical unit that consists of a flexible or rigid tube with a display or an eyepiece on one end, a camera or objective lens on the other, and they are linked together by an electrical or optical system in between. 

In some cases, the optical system is enclosed by optical fibers that are used to illuminate the remote object. The internal image of the illuminated target is created by the objective lens, and it is magnified by the eyepiece which shows it to the viewer’s eyes. 

Flexible or rigid borescopes may be equipped with a video or imaging device. Similar instruments are called endoscopes, and they are used for medical purposes.


What are borescopes used for?

Borescopes are instruments used for visual inspections of areas that cannot be accessed by other means. Also, they are useful in cases where an inspection might cause destruction, or when it is too expensive or time-consuming. Endoscopes are similar devices and they are used inside the human body. 

Borescopes are used in non-destructive testing techniques to recognize imperfections and defects. To be more exact, these optical instruments are mostly used in the visual inspection of diesel engines, aircraft engines, truck and automotive engines, steam turbines, or aero-derivative industrial gas turbines. 

Due to safety as well as maintenance requirements, steam and gas turbines require special attention. In the case of engines, visual inspection is required in order to prevent additional maintenance that can become particularly expensive for large turbines. 

Borescopes are also utilized in the manufacturing of cast or machined parts to examine significant interior surfaces for complete through-holes, burrs, or surface finish. There are other general uses that include building inspections, forensic applications in law enforcement, or in gunsmithing for analyzing the interior bore of firearms. 

As an interesting fact, in World War II, primitive forms of borescopes were utilized to check the interior bores of large guns for defects, hence the bore-scope name. 


Flexible borescopes

The standard flexible borescope comprises a package of optical fibers that divide the image into pixels. This is also known as a fiberscope, and it can be used to gain access to cavities that are around a bend like combustion chambers, to verify the condition of the compressed air inlets, seals, and turbine blades, without dismantling the engine. 

Conventional flexible borescopes may suffer from pixelation as well as pixel crosswalk because of the fiber image guide. Therefore, the quality of the images differs a lot among various models. It really depends on the number of fibers and the construction that was used in the fiber image guide. 

There are high-end flexible borescopes that provide a visual grid on image captures in order to aid in the evaluation of the size of any area with an issue. Other important features are the field of view, the articulation mechanism components, angles of view of the objective lenses, as well as the range of articulation. 

The fiber content from the flexible relay is also essential in providing the best possible resolution. There is a minimum amount of 10,000 pixels required, but the best images are captured with higher numbers in the range of 15,000 and 22,000 for borescopes with larger diameters. 

Moreover, the possibility to control the light at the end of the insertion tube allows the user to make the necessary adjustments in order to improve the clarity of the still images or video.



Rigid borescopes

These devices are similar to fiberscopes except that they offer a better image at a lower cost compared to flexible borescopes. Only objects that are in a straight line can be accessed using a rigid borescope. They are commonly used to examine hydraulic manifold bodies, automotive cylinders, fuel injectors, and for gunsmithing as well. 

Usually, users select a borescope based on image clarity and ease of access. The optical systems in rigid borescopes can be of three types: achromatic doublets, gradient index rod lenses, and Harold Hopkins rod lenses. 

For borescopes with a larger diameter, the achromatic doublet relays work well. However, as the diameter of the unit becomes smaller, the Hopkins rod lens, as well as the index rod lens, provide better images. For smaller borescopes of under 3mm diameters, the gradient index lenses work best.


Semi-rigid borescopes

This type is a step up from rigid borescopes because they are bendable and perfect for confined spaces that do not allow room for articulation. These models are more durable and forgiving than the rigid ones due to the technological progression as well as their ability to bend. 

However, semi-rigid borescopes are known for offering poor image quality compared to other types of borescopes. This may discourage users that require high-resolution image viewing. The image suffers from pixelation meaning that the photos and the viewing screen display small black dots which are caused by broken pixels. 

Unfortunately, as the strand begins to break down, they cannot be repaired, and the entire unit needs to be replaced. For these reasons, semi-rigid borescopes are less popular with users.



Since we mentioned this term a couple of times, we should discuss it in more detail. A fiberscope can bundle together between 3,000 and 30,000 fiber strands. It uses these fibers to transmit an image from the lens that is closest to the target through these fibers to a relay lens. The captured image can be seen directly through the eyepiece. 

There is also the possibility to attach a camera that displays the picture on a monitor. Fiberscopes are flexible, and they can be used for examinations in which straight-line access is impossible. There are models that are classified as semi-rigid, but there are also the ones available with articulation.


Video borescopes

A video borescope, otherwise known as an inspection camera, is very similar to the flexible unit except that it is equipped with a tiny camera at the end of the flexible tube. The end of the insertion tube contains a light that makes it possible to catch still or video images deep inside engines, equipment, or other dark and hard-to-access areas. 

Since this is a tool used for visual inspections, the fact that still images or video are captured for later examination is a great advantage. Moving on, there is a display at the other end that shows the camera view. The viewing position can be changed using a joystick or a similar control in some models. 

An inexpensive electrical cable replaces the complex fiber optic waveguide from the traditional borescope. Therefore, video borescopes are much cheaper and can provide a better resolution. Of course, this also depends on the camera specs. 



The prices for high-end video borescopes range between $8,000 and $50,000, and they depend on the manufacturer, specifications, and options. The battery-operated, easy-to-use video borescopes with 3-inch LCD displays became available around 2012 from a few manufacturers, and the prices ranged between $100 and $400. 

On most of these items, the flexible tube and the video camera are submersible. Newer models began to provide improved features like a better resolution, a lower cost, adjustable illumination, and even the option to replace the built-in display with a computer connection, like a USB cable. The good news is that hobbyist models of this kind are currently available starting from $10.


Differences between flexible and rigid borescopes

Besides the fact that one is flexible and the other one not, the two borescopes have a lot in common. They both have objective lenses that create an image of the target on the relay system. Both have eyepiece lenses that magnify the image from the relay system so the user can see it. 

The big difference between the two types is in the relay itself. In order to permit flexibility, the image is transferred from the objective lens to the eyepiece by a bunch of optical fibers, and not by a system of lenses. 

Light cannot get out through the side once it enters a fiber. Therefore, it follows the fiber around the bends and twists. The ends of the fibers should occupy exactly the same respective position at both the eyepiece ends and the lenses, or the image becomes scrambled.



Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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