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In third-order astigmatism, the tangential rays (in the tangential plane) and sagittal rays (in the sagittal plane) form foci at different distances along the optic axis. These foci are called the tangent focus and sagittal focus, respectively. In the presence of astigmatism, an off-axis point on the object is not sharply imaged by the optical ...
Coma of a single lens. Each cone of light focuses on different planes along the optical axis. In optics (especially telescopes), the coma (/ ˈ k oʊ m ə /), or comatic aberration, in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components that results in off-axis point sources such as stars appearing distorted ...
An off-axis optical system is an optical system in which the optical axis of the aperture is not coincident with the mechanical center of the aperture. The principal applications of off-axis optical systems are to avoid obstruction of the primary aperture by secondary optical elements, instrument packages, or sensors, and to provide ready access to instrument packages or sensors at the focus.
Off-axis feed or offset-feed The primary reflector is asymmetric, with the focus, and the feed, located to one side, outside the beam area. This avoids the problem of the feed obstructing the beam. This avoids the problem of the feed obstructing the beam.
The basic layout of a collimator sight is a closed tube with a lens at its open end and a luminous reticle mounted near the closed end at the focus of the lens, creating an optical collimator. The reticle is illuminated by an electronic light source (an incandescent light bulb or, more recently, a light-emitting diode ) or by ambient light ...
The KH-11 Kennen (or perhaps the now cancelled Future Imagery Architecture) telescopes may be a three-mirror anastigmat, since the spare telescopes given to NASA by the National Reconnaissance Office are of this form. The Extremely Large Telescope will be a three-mirror anastigmat design, with two additional flat fold mirrors.
Example of a particle collimator. A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spatial cross section of the beam to become smaller (beam limiting device).