Telecentrične leče
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FOV = Field Of View, vidno polje. Za moje pojme ima vezo s kotom padanja svetlobe. In se mi zdi, da je potem FOV kvečjemu enak površini leče.
Če leče niso telecentrične, je kot padanja svetlobe različen od 90/0° in se FOV veča z razdaljo do objekta.
Sem pa prebral, da obstajajo tudi dual telecentraične leče, ki imajo kot padanja 90°v smeri proti objektu IN v smeri proti senzorju.
Zdaj pa ne vem, kako točno to izgleda.
lp
Če leče niso telecentrične, je kot padanja svetlobe različen od 90/0° in se FOV veča z razdaljo do objekta.
Sem pa prebral, da obstajajo tudi dual telecentraične leče, ki imajo kot padanja 90°v smeri proti objektu IN v smeri proti senzorju.
Zdaj pa ne vem, kako točno to izgleda.
lp
Aha, mislim da vem kaj te muči. Telecentrične leče - manjši kot - manjši FOV. Vendar ni prava logika, ker mešaš kot padanja svetlobe na senzor s celotnim vidnim poljem objektiva.
FOV je za isto goriščno razdaljo pri isti velikosti senzorja vedno enak, ne glede na tehnologijo leč. Oz. če se izražamo v 35mm ekvivalentu ima Oly 300mm ekvivalent (čeprav je dejansko 150mm objektiv) isti FOV kot 300mm na FF Nikonu.
In FOV se izraža v stopinjah, ker je to kot pogleda in ga ne moreš primerjat s površino leče. Reče se mu tudi Angle of View, torej je to kot.
Nazoren prikaz ožanja kota pogleda pri večanju goriščne razdalje je tukaj. Vidiš, da površina leče ni noben faktor pri FOV.
FOV je za isto goriščno razdaljo pri isti velikosti senzorja vedno enak, ne glede na tehnologijo leč. Oz. če se izražamo v 35mm ekvivalentu ima Oly 300mm ekvivalent (čeprav je dejansko 150mm objektiv) isti FOV kot 300mm na FF Nikonu.
In FOV se izraža v stopinjah, ker je to kot pogleda in ga ne moreš primerjat s površino leče. Reče se mu tudi Angle of View, torej je to kot.
Nazoren prikaz ožanja kota pogleda pri večanju goriščne razdalje je tukaj. Vidiš, da površina leče ni noben faktor pri FOV.
Object-space telecentric lenses
Normal lenses exhibit varying magnification for objects at different distances from the lens. This causes several problems for machine vision and other applications:
the apparent size of objects changes with distance from the camera
some features or objects may be hidden by objects that are closer to the lens
the apparent shape of objects varies with distance from the center of the field of view (FOV). Objects appearing close to the edges are viewed from an angle, while objects near the centre of the FOV are viewed frontally (circles near the centre of the FOV become ellipses when moved towards the periphery).
Telecentric lenses, on the other hand, have the same magnification at all distances. An object-space telecentric lens creates images of the same size for objects at any distance and has constant angle of view across the entire field of view. An object that is too close or too far from the lens may still be out of focus, but the resulting blurry image will be the same size as the correctly-focused image would be.
Because their images have constant magnification and geometry, telecentric lenses are used for metrology applications, when a machine vision system must determine the precise size of objects independently from their position within the FOV and even when their distance is affected by some degree of unknown variations. These lenses are also commonly used in optical lithography, for forming patterns in semiconductor chips.
Object-space telecentric lenses have an entrance pupil infinitely far behind the lens; this is, if you look in the front, the apparent aperture is very far away.
Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. This is partly due to the extra components needed to achieve telecentricity, and partly because the object or image lens elements of an object or image-space telecentric lens must be at least as large as the largest object to be photographed or image to be formed . As of 2006, these lenses can range in cost from hundreds to thousands of US dollars or euros, depending on quality. Because of their intended applications, telecentric lenses often have higher resolution and transmit more light than normal photographic lenses.
In order to optimize the telecentric effect, these lenses are often used in conjunction with telecentric illuminators, which produce a parallel light flow, often from LED sources.
http://en.wikipedia.org/wiki/Telecentric_lens
Tole poudarjeno mene zanima.
lp
Normal lenses exhibit varying magnification for objects at different distances from the lens. This causes several problems for machine vision and other applications:
the apparent size of objects changes with distance from the camera
some features or objects may be hidden by objects that are closer to the lens
the apparent shape of objects varies with distance from the center of the field of view (FOV). Objects appearing close to the edges are viewed from an angle, while objects near the centre of the FOV are viewed frontally (circles near the centre of the FOV become ellipses when moved towards the periphery).
Telecentric lenses, on the other hand, have the same magnification at all distances. An object-space telecentric lens creates images of the same size for objects at any distance and has constant angle of view across the entire field of view. An object that is too close or too far from the lens may still be out of focus, but the resulting blurry image will be the same size as the correctly-focused image would be.
Because their images have constant magnification and geometry, telecentric lenses are used for metrology applications, when a machine vision system must determine the precise size of objects independently from their position within the FOV and even when their distance is affected by some degree of unknown variations. These lenses are also commonly used in optical lithography, for forming patterns in semiconductor chips.
Object-space telecentric lenses have an entrance pupil infinitely far behind the lens; this is, if you look in the front, the apparent aperture is very far away.
Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. This is partly due to the extra components needed to achieve telecentricity, and partly because the object or image lens elements of an object or image-space telecentric lens must be at least as large as the largest object to be photographed or image to be formed . As of 2006, these lenses can range in cost from hundreds to thousands of US dollars or euros, depending on quality. Because of their intended applications, telecentric lenses often have higher resolution and transmit more light than normal photographic lenses.
In order to optimize the telecentric effect, these lenses are often used in conjunction with telecentric illuminators, which produce a parallel light flow, often from LED sources.
http://en.wikipedia.org/wiki/Telecentric_lens
Tole poudarjeno mene zanima.
lp
