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Borescope knowhow

Borescopes and fiberscopes are technical devices with which the inside of technical hollow bodies is viewed in the industrial sector. On this page you will find useful terms and explanations around the construction of endoscopes.

Field of view and wide angle

The field of view, also called angle of view or aperture angle, indicates the visible image section. It is specified in degrees. As of 80° and above, it is called a wide angle. The field of view is independent of the direction of view of the borescope/fiberscope. In its standard product range, SCHÖLLY offers fields of view ranging from 30° - 100°.   

Endoscopy Knowledge - field of view

Direction of view

The inspection site inside the object is not always positioned opposite the borescope or fiberscope. This is why there are different directions of view. This makes it possible, for example, to look to the side or diagonally to the front. The direction of view is specified in degrees in relation to the shaft. SCHÖLLY offers directions of view ranging from 0° - 110°.

Working diameter and working length

The working diameter is the outer diameter of the borescope/fiberscope shaft. In principle, the working diameter selected should be as large as possible. However, the depth of field range and direction of view must also be taken into account. The working length is the length of the borescope shaft.

Image bundle

In fiberscopes (also called flexible borescopes) the transmission of images and light takes place via image bundles. Image bundles consist of individual fibers which have the same relative position to each other at the input and output. Each fiber transmits a pixel from the objective to the ocular. The quality of the image depends on the number of pixels and the size of each individual fiber. The image bundle systems ensure the flexibility and movability of the probe.


Depth of field

The depth of field is the area in which the borescope/fiberscope gives a focused image of the object.


Light guide connection

Flexible and rigid borescopes have a light guide connection to illuminate the inspection site via an external light source. The light guide connects the light source to the borescope or fiberscope. The light guide connector used in our borescopes/fiberscopes is a SCHÖLLY standard connector.


The ocular is the part of the borescope and fiberscope through which you look with the eye at the inspection site. For a digital display of the inspection, a camera/camera head can be connected to the ocular and the images can be displayed on a monitor. Our borescopes and fiberscopes are equipped with a DIN ocular and these fit all SCHÖLLY camera heads. With a SCHÖLLY endocoupler, borescopes can also be connected to other endoscopic cameras.

Tip deflection

With a deflectable tip, flexible borescopes can be used to examine hollow spaces from various angles of view. The tip can be deflected in two-way or four-way direction via an adjusting lever on the device.


The focus ring can be used to adjust the focus of the image within the defined working area.

Mirror tubes

Mirror tubes are attachments that the user can use to change the direction of view of the borescope. By turning the reflector tube during the inspection, the user can gain a 360-degree view. Mirror tubes are available with different directions of view. Directions of view of 70°, 90° or 110° are available.

Interchangeable objectives and objective tubes

For its universal borescopes, SCHÖLLY offers a range of interchangeable objectives and rotatable objective tubes with different directions and fields of view. The rotatable objective tubes can be used to gain a 360-degree view inside the inspection object. The user only needs a basic device to use the interchangeable objectives and rotatable objective tubes to adapt their equipment to different requirements within a similar diameter range. Directions of view ranging from 0° - 90° are available.