Our client required a very specific image visualization, but in more general cases, the camera size and resolution should be taken in consideration when designing the objective lens. The final optical design step that needs to be implemented is adding a camera (or eyepiece) to observe the image. One advantage of this relay lens system is that, if the borescope needs to be extended further (or to be reduced), it will be a matter of removing relay lens sections without affecting the camera or objective lens. The relay lens translates image 1:1 while the aperture of the designed relay lens coincides with the objective lens and the relay lens allows image translation without significant degradation of image quality. That is, 4 or 5 relay lenses with an extension of 100-150mm each and concatenated one after the other to achieve the required borescope length. The borescope required an extension between 400-600 mm: instead of creating a single relay lens for the total length, we divided the length into 4-5 unit elements. During the optimization stage, we carefully pick the best materials to reduce the amount of aberrations. We designed this objective lens based on the client’s requirements of resolution, FOV, wavelength range (900-1700 nm in this case), and working distance. The objective lens forms the initial image and provides the needed optical parameters and image quality. The objective lens is the key part of the borescope system. An objective lens creates an intermediate image that is picked up by a relay lens and is then translated to an image sensor (not shown) The relay lens translates this image from the objective lens to the imaging sensor (not shown).įigure 1. In order to design (or choose the correct) objective lens, there are different parameters that need to be considered such as working distance, field of view, resolution at the camera sensor, image size, etc. The particular borescope shown in Figure 1 contains an objective lens and a set of relay lenses. They can be made with rigid or flexible components with an objective lens on one end and a camera or eyepiece on the other. What is a borescopeīorescopes are usually used when there is a need to inspect narrow or difficult access locations. Here we describe some steps that were taken to design an optical relay system for a client that needed a custom borescope. Relay lenses are used when the user cannot be physically close to the object being observed (like an endoscope) or when images need to be inverted/rectified (like in a telescopic sight).
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