Calculations with Optical Instruments
Calculations with Various Optical Instruments
Focal Length of a Lense
The focal length f is the distance of a lense (or mirror) to the point where a light source, which is shining through the instrument, is focussed most.
The world we live in is three-dimensional, but the image perceived by the eyes and brain is only two-dimensional. Both eyes together also convey a sense of depth in the third dimension. However, through a lens, the depth of field, if present, appears blurred, which is why we often only look through it with one eye. Therefore, lenses magnify lengths and areas. The value of magnification refers to the length, the magnification of a surface area is this value squared (when doubling a surface in each direction, its area gets quadrupled).
Example: if the lens magnifies three times, then the lengths triple and the area increases ninefold.
The term optics comes from Greek and means the study of vision. Accordingly, optical devices are those that influence visual processes. A very simple optical device is a lens. A convex lens, i.e. one that is curved outwards, bundles the light and concentrates it on one point, the focal point. The distance of the focal point from the lens is the focal length, which depends on the curvature of the lens; the more curved it is, the closer the focal point is and the more magnification is achieved. A sharp, magnified image can only be seen at this focal point. An optical device that only uses one lens is the magnifying glass, which is simply a convex lens with a frame and handle. Glasses are two lenses next to each other, although the structure of the individual lenses is somewhat more complicated. Several lenses one after the other can be found in a microscope, telescope or binocular and in an objective.
Matching websites: Angular Diameter, Photographic Exposure, Convert Length Units, Lens as Geometric Solid.
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