Coincidence rangefinder
Coincidence rangefinders are optical-mechanical devices for measuring distances . They were mainly used in the military and photo technology, but have now been almost completely replaced by laser and infrared rangefinders. A distinction is made between sectional and mixed image rangefinders.
Basics
Conceptually, coincidence rangefinders are based on the principle of triangulation . If one considers an object from two different points, it can be based on the length of the connection between the two points - the so-called base length - and the viewing angle in accordance with the law of sines calculate the distance to the object of observation.
In a coincidence rangefinder, the base is formed by the two mirrors. While one mirror is fixed, the other mirror is rotatably mounted. The images of the two mirrors are brought together in the eyepiece . If both mirrors are aimed precisely at the target, the images are identical. If the alignment of the movable mirror deviates, its image is shifted in the eyepiece. Using the angle of the moving mirror, the distance can be calculated because the base line and angle of the fixed mirror are known.
construction
Coincidence range finders are monocular devices. Even with coincidence rangefinders from Barr and Stroud , only one eyepiece is used for the image display; the scale is reflected in the other . This has the advantage that the distance can be read off without taking your eye off the eyepiece. Instead of the mirrors described above, prisms are mostly used.
Because of their monocular construction, coincidence rangefinders, in contrast to spatial image rangefinders, do not place any special demands on the spatial vision of their user and can be used by practically everyone. This ease of use has greatly encouraged their dissemination. Coincidence rangefinders can display high-contrast and sharp-contoured targets well, with weak contrast, missing contours such as B. Clouds and fast moving targets they are less suitable.
Despite their fundamentally simple structure, coincidence rangefinders are complex optical-mechanical devices. The required accuracy sometimes leads to high costs for optical and temperature compensation. Furthermore, in the military sector, high demands are placed on the robustness of the devices. The accuracy of the distance measurement depends, among other things, on the size of the baseline. This leads to very large devices, especially in the military sector. Rangefinders used by the military had to be adjusted several times a day in order to achieve sufficient accuracy. In photo cameras , the measurement range and precision are limited due to the specified size. These disadvantages led to the fact that coincidence rangefinders were increasingly replaced by electronic rangefinders from the 1990s .
Split image rangefinder
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In the case of a sectional image rangefinder, the image in the eyepiece is divided into an upper and lower half, which must be brought into line. You need vertical lines of contrast to work properly.
Cross-sectional rangefinders have been in use in the military since the 1890s, as guns reached a range from the 1880s that no longer permitted direct aiming . While with direct aiming the target is aimed directly at the sight on the weapon, with indirect aiming the setting of the guideline values - side and elevation angles - is only based on calculations. The prerequisite for this is the determination of the distance to the target. Barr and Stroud presented the first cross-sectional rangefinder developed at the request of the British Admiralty in 1891.
The Royal Navy held on to the cross- sectional rangefinder until World War II , while other naval forces preferred spatial rangefinders. Comparisons made by the US Navy in 1941 showed that there are no significant differences between spatial and coincidence rangefinders in terms of the accuracy of the measurement.
In the land forces, however, coincidence rangefinders established themselves early on, which made significantly less demands on the selection and training of operators. This enabled the mass use of these rangefinders in artillery, air defense and in tanks. Spatial image rangefinders were only preferred for the anti-aircraft artillery, as they are much more suitable for permanent observation. After the Second World War, battle tanks were increasingly equipped with cross-sectional rangefinders, which significantly increased the probability of hits. Both the American M60 and the Soviet T-72 initially had cross-sectional rangefinders. These were replaced by laser rangefinders in the 1980s when these devices could be manufactured in large numbers.
Analog single-lens reflex cameras often had a slice image indicator that shows a similar image in the eyepiece to a slice image rangefinder. In the case of a cross-sectional image indicator, the distance to the object is not measured, but only shows whether the lens is focused on the object to be photographed.
Reversing image rangefinder
In the case of an inverted image rangefinder, too, the image in the eyepiece is divided into an upper and lower half, which must be brought into line. Here, however, the image is not cut up, but the second image is shown upside down.
Reversing image rangefinders were particularly widespread in German armies. The range measuring devices used by the German anti-aircraft artillery during the First World War were reversing image range finders. First of all, the range finder used in the field artillery and developed by the Felda company with a base length of 1.25 m was used. However, this was soon too imprecise, so only targets up to a distance of 4000 m could be measured with sufficient precision. From 1916, a reversing image rangefinder with a measuring base of two meters in length was used, with which targets could be measured up to a distance of 6000 m. However, with the increasing speed of the air targets, it became difficult to keep the air target in sight while measuring the distance. For this reason, the air defense in Germany also switched to using the spatial range finders introduced by the navy. In other military areas, where the objects to be observed moved less quickly or only in two dimensions, coincidence rangefinders continued to be used. The NVA the DDR procured with the multimeter for pioneers (UMG-Pi) again an inverted image rangefinder. The device with a base length of 52 cm enlarged 14 times. With it, targets at distances between 15 and 3000 m could be measured, the measurement error was 20 m.
Mixed image rangefinder
Mixed image range finders , also known as telemeters , were mainly used in rangefinder cameras . Due to the design, the baseline is very small here, and the accuracy is sufficient for most photographic purposes. Mixed image rangefinders can be found in rangefinder cameras from Contax , which played a pioneering role in the design and introduction of this technology, but also by other camera manufacturers. For the first time, Contax combined the viewfinder image and rangefinder in one eyepiece.
An extension of the mixed image rangefinder is the phase detection autofocus, which was first used in 1977 on the Konica C35-AF . In contrast to active autofocus systems that only work with one beam path, the image of the object is recorded by two sensors arranged on the base line. From the offset of the two images, the camera calculates the distance to the object being viewed and focuses the lens.
A rangefinder was used in the Leopard 1 battle tank , which could work as a mixed image or spatial image rangefinder.
See also
- Distance measurement
- Rangefinder (camera)
- Space image range finder
- Stadiametric distance measurement
Individual evidence
- ^ Rangefinders and Tracking, Summary Technical report of NDRC, Division 7 (Fire Control) , Volume 2, pp. 17f. (English)
- ↑ The fire control system of the M60A3 main battle tank
- ↑ The fire control system of the T-72, T-72A and T-72B main battle tanks
- ↑ see Werner Müller: Horchgeräte - command devices and searchlights of the heavy flak
- ↑ see general information on optical distance measuring devices ( Memento from October 22, 2012 in the Internet Archive )
- ↑ Photography information, viewfinder cameras: distance setting, mixed image rangefinder
- ↑ see Martin Bantel: Messgeräte-Praxis , p. 177
- ↑ The fire control system of the Leopard 1 battle tank
literature
- Alexander Wilhelm Gleichen: The theory of modern optical instruments: an auxiliary and exercise book for physicists and designers of optical workshops, as well as for engineers in the service of the army and the navy , F. Enke, 1911
- Richard Lenk, Walter Gellert: Brockhaus ABC Physik, Volume 1 , FA Brockhaus, 1972
- Association for the Promotion of Photography, Berlin, Reich Association of German Amateur Photographers: Fotografische Rundschau und Mitteilungen, Volume 70 , 1933
- Deutscher Verein für Vermessungs, Deutscher Geometerverein: Zeitschrift für Vermessungswesen, Volume 43 , K. Wittwer, 1914
- Emil-Heinz Schmitz: Handbook on the history of optics: The step into the XX. Century , Volume 4, Part 2, JP Wayenborgh, 1984
- Emil-Heinz Schmitz: Handbook on the history of optics: The step into the XX. Century , Volume 5, Part 3, JP Wayenborgh, 1993
- Georg Gehlhoff: Textbook of technical physics for advanced students and engineers: optics; Electronics , Johann Ambrosius Barth Verlag , 1924
- Albert König: The telescopes and range finders , J. Springer, 1923
- Christian Hofe: Fernoptik , JA Barth, 1921
- Martin Bantel: Messgeräte-Praxis , Hanser Verlag, 2004
- Paul Kneiphoff, Michael Brix: The air defense of the NVA , Verlag am Park, 2005
- Werner Müller: Listening devices - command devices and searchlights of the heavy flak , Waffen-Arsenal special volume S-21, Podzun-Pallas