![]() ![]() This can be used to slightly adjust the working distance and magnification while losing a little bit of telecentricity. Some commercial telecentric lenses, however, do feature a focus ring. A truly telecentric lens has no focus ring to adjust the position of the focal plane. ![]() Because of their intended applications, telecentric lenses often have higher resolution and transmit more light than normal photographic lenses.Ĭommercial object-space telecentric lenses are often characterized by their magnification, working distance and maximum image circle or image sensor size. In contrast to entocentric lenses where lenses are made larger to increase the aperture for increased collection of light or shallower depth of field, a larger diameter (but otherwise similar) object-space telecentric lens is not faster than a smaller lens. The front element in an object-space telecentric lens is often much larger than the camera mount. This is partly due to the extra components needed to achieve telecentricity, and partly because the first element in an object-space telecentric lens must be at least as large as the largest object to be imaged. Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. Objects at this distance are in focus and imaged sharply onto the image sensor at flange focal distance in the camera.Īn object that is closer or farther is out of focus and may be blurry, but will be the same size regardless of distance. Object-space telecentric lenses have a working distance. Object-space telecentric imaging where the aperture is in the back focal plane of the objective.Īn object-space telecentric lens has the entrance pupil at infinity and provides an orthographic projection instead of the perspective projection in an entocentric lens. In an object-space telecentric lens the image size does not change with the object distance, and in an image-space telecentric lens the image size does not change with the image-side distance from the lens. A hypercentric lens produces larger images the farther the object is away.Ī telecentric lens can be object-space telecentric, image-space telecentric, or bi-telecentric (also double-telecentric). An entocentric lens has a smaller magnification for objects farther away objects of the same size appear smaller the farther they are away. ![]() For such a lens the chief ray originating at any point off of the optical axis is never parallel to the optical axis, neither in front of nor behind the lens.Ī non-telecentric lens exhibits varying magnification for objects at different distances from the lens. In particular, a single lens without a separate aperture stop is entocentric. If a lens is not telecentric, it is either entocentric or hypercentric. The aperture stop selects the rays that are passed through the lens and the specific selection is what makes a lens telecentric. Telecentricity is not a property of the lenses inside the compound lens but is established by the location of the aperture stop in the lens. Commercially available telecentric lenses are often compound lenses that include multiple lens elements, for improved optical performance. This makes the chief rays (light rays that pass through the center of the aperture) on the other side of the lens parallel to the optical axis for any point in the field of view. The simplest way to make a lens telecentric is to put the aperture stop at one of the lens's focal points. Telecentric lenses are often used for precision optical two-dimensional measurements or reproduction and other applications that are sensitive to the image magnification or the angle of incidence of light. Bi-telecentric lens with 208 mm diameter front element and a C-mount camera interfaceĪ telecentric lens is a special optical lens (often an objective lens or a camera lens) that has its entrance or exit pupil, or both, at infinity. ![]()
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