224:, while absorbing the remainder. They can usually pass long wavelengths only (longpass), short wavelengths only (shortpass), or a band of wavelengths, blocking both longer and shorter wavelengths (bandpass). The passband may be narrower or wider; the transition or cutoff between maximal and minimal transmission can be sharp or gradual. There are filters with more complex transmission characteristic, for example with two peaks rather than a single band; these are more usually older designs traditionally used for photography; filters with more regular characteristics are used for scientific and technical work.
582:(UV) filters block ultraviolet radiation, but let visible light through. Because photographic film and digital sensors are sensitive to ultraviolet (which is abundant in skylight) but the human eye is not, such light would, if not filtered out, make photographs look different from the scene visible to people, for example making images of distant mountains appear unnaturally hazy. An ultraviolet-blocking filter renders images closer to the visual appearance of the scene.
36:
628:
as edge filters), are described by the cut-on wavelength at 50 percent of peak transmission. In fluorescence microscopy, longpass filters are frequently utilized in dichroic mirrors and barrier (emission) filters. Use of the older term 'low pass' to describe longpass filters has become uncommon; filters are usually described in terms of wavelength rather than frequency, and a "
700:, angular orientations, and wavelength range. The parameters of the filters are designed by proper choice of the grating parameters. The advantage of such filters are the few layers needed for ultra-narrow bandwidth filters (in contrast to dichroic filters), and the potential decoupling between spectral bandwidth and angular tolerance when more than 1 mode is excited.
133:
793:
Some examples of filters that would provide this kind of filtering would be earth elements embedded or coated on glass, but practically speaking it is not possible to do perfect filtering. A perfect filter would remove particular wavelengths and leave plenty of light so a worker can see what he/she
627:
A longpass (LP) Filter is an optical interference or coloured glass filter that attenuates shorter wavelengths and transmits (passes) longer wavelengths over the active range of the target spectrum (ultraviolet, visible, or infrared). Longpass filters, which can have a very sharp slope (referred to
679:
A shortpass (SP) Filter is an optical interference or coloured glass filter that attenuates longer wavelengths and transmits (passes) shorter wavelengths over the active range of the target spectrum (usually the ultraviolet and visible region). In fluorescence microscopy, shortpass filters are
750:
to better view below the surface of the water and better vision for a driver. Light from a clear blue sky is also polarized, and adjustable filters are used in colour photography to darken the appearance of the sky without introducing colours to other objects, and in both colour and
242:
optical filters are used to restrict light passed to the spectral band of interest, e.g., to study infrared radiation without visible light which would affect film or sensors and overwhelm the desired infrared. Optical filters are also essential in fluorescence applications such as
615:. They are useful for making photographic exposures longer. A practical example is making a waterfall look blurry when it is photographed in bright light. Alternatively, the photographer might want to use a larger aperture (so as to limit the
478:
Dichroic filters are particularly suited for precise scientific work, since their exact colour range can be controlled by the thickness and sequence of the coatings. They are usually much more expensive and delicate than absorption filters.
261:
of filters designed for scientific work, and sell in larger quantities at correspondingly lower prices than many laboratory filters. Some photographic effect filters, such as star effect filters, are not relevant to scientific work.
659:. Both of these filters can also be made tunable, such that the central wavelength can be chosen by the user. Band-pass filters are often used in astronomy when one wants to observe a certain process with specific associated
394:
Optical filtering was first done with liquid-filled, glass-walled cells; they are still used for special purposes. The widest range of color-selection is now available as colored-film filters, originally made from animal
585:
As with infrared filters there is a potential ambiguity between UV-blocking and UV-passing filters; the latter are much less common, and more usually known explicitly as UV pass filters and UV bandpass filters.
891:
Optical Filter Design and
Analysis: A Signal Processing Approach, Christi K. Madsen, Jian H. Zhao, Copyright © 1999 John Wiley & Sons, Inc., ISBNs: 0-471-18373-3 (Hardback); 0-471-21375-6 (Electronic)
475:. Their layers form a sequential series of reflective cavities that resonate with the desired wavelengths. Other wavelengths destructively cancel or reflect as the peaks and troughs of the waves overlap.
644:
Band-pass filters only transmit a certain wavelength band, and block others. The width of such a filter is expressed in the wavelength range it lets through and can be anything from much less than an
696:
or 2D hole array. Such filters are normally transparent, but when a leaky guided mode of the waveguide is excited they become highly reflective (a record of over 99% experimentally) for a particular
810:
distribution in a radiation beam. It is also known as linearly variable filter (LVF). It is used in various optical sensors where wavelength separation is required e.g. in hyperspectral sensors.
603:
have a constant attenuation across the range of visible wavelengths, and are used to reduce the intensity of light by reflecting or absorbing a portion of it. They are specified by the
257:
are a particular case of optical filters, and much of the material here applies. Photographic filters do not need the accurately controlled optical properties and precisely defined
503:
are another variation: transparent cubes or fibers whose polished ends form mirrors tuned to resonate with specific wavelengths. These are often used to separate channels in
376:
619:); adding an ND filter permits this. ND filters can be reflective (in which case they look like partially reflective mirrors) or absorptive (appearing grey or black).
746:. Reflections, especially from water and wet road surfaces, are partially polarized, and polarized sunglasses will block some of this reflected light, allowing an
446:
have been added. Colored glass optical filters, although harder to make to precise transmittance specifications, are more durable and stable once manufactured.
905:
534:
The term "infrared filter" can be ambiguous, as it may be applied to filters to pass infrared (blocking other wavelengths) or to block infrared (only).
888:
306:
186:
278:. As a linear material, the absorption for each wavelength is independent of the presence of other wavelengths. A very few materials are
497:. It uses two mirrors to establish a resonating cavity. It passes wavelengths that are a multiple of the cavity's resonance frequency.
922:
656:
494:
119:
759:
from objects and water. Much older than g.m.r.f (just above) these first (and some still) use fine mesh integrated in the lens.
508:
954:
472:
53:
464:(also called "reflective" or "thin film" or "interference" filters) can be made by coating a glass substrate with a series of
688:
A relatively new class of filters introduced around 1990. These filters are normally filters in reflection, that is they are
100:
57:
806:
so constructed that its thickness varies continuously or in steps in the shape of a wedge. The filter is used to modify the
270:
In general, a given optical filter transmits a certain percentage of the incoming light as the wavelength changes. This is
182:, which specifies how the magnitude and phase of each frequency component of an incoming signal is modified by the filter.
72:
210:
202:
985:
1016:
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504:
79:
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709:
412:
345:
46:
1046:
564:
248:
86:
1080:
612:
668:
552:
544:
404:
291:
271:
244:
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Infrared-passing filters are used to block visible light but pass infrared; they are used, for example, in
68:
600:
595:
137:
568:
171:
819:
735:
731:
697:
664:
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416:
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254:
227:
692:
in transmission. They consist in their most basic form of a substrate waveguide and a subwavelength
854:
824:
807:
756:
439:
190:
563:) to prevent unwanted heating due to infrared radiation. There are also filters which are used in
317:
of the incident light, regardless of the mechanism by which it is attenuated. Some filters, like
859:
844:
829:
560:
468:. Dichroic filters usually reflect the unwanted portion of the light and transmit the remainder.
309:; for intense light, that can cause significant heating of the filter. However, the optical term
258:
230:(where some special effect filters are occasionally used as well as absorptive filters), in many
179:
175:
286:
depends on the intensity and the combination of wavelengths of the incident light. Transparent
633:
443:
400:
299:
275:
648:
to a few hundred nanometers. Such a filter can be made by combining an LP- and an SP filter.
551:
light. Mid-infrared filters are often used as heat-absorbing filters in devices with bright
548:
461:
279:
194:
93:
929:
803:
629:
604:
556:
465:
455:
338:
790:
must meet ANSI Z87:1 (a safety glasses specification) in order to protect human vision.
834:
787:
645:
616:
483:
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235:
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660:
408:
383:
333:
283:
148:
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689:
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206:
163:
185:
Filters mostly belong to one of two categories. The simplest, physically, is the
869:
849:
783:
775:
763:
743:
718:
that are stacked together to form LP, BP, and SP filters for these wavelengths.
652:
579:
526:
only allow a narrow range of wavelengths (essentially a single colour) to pass.
512:
314:
35:
889:
Transmission curves of many filters for monochrome photography, Schneider, p.1
739:
326:
310:
217:
155:
132:
993:
1024:
727:
608:
424:
239:
17:
714:
Filters for sub-millimeter and near infrared wavelengths in astronomy are
906:
Transmission curves of many filters for monochrome photography, Schneider
779:
730:
or polarization filter, which blocks or transmits light according to its
786:
light that may be harmful to human eyes. Therefore, optical filters on
747:
693:
428:
396:
231:
159:
567:
video cameras to block IR due to the high sensitivity of many camera
500:
487:
318:
198:
216:
Optical filters selectively transmit light in a particular range of
766:, so that each eye will see a distinct image from a single source.
680:
frequently employed in dichromatic mirrors and excitation filters.
435:
221:
151:
131:
671:
are examples where Lyot and Fabry–Pérot filters are being used.
490:
to separate a beam of light into different coloured components.
167:
547:
are designed to block or reflect infrared wavelengths but pass
909:
908:. See Redhancer 491 for a very complex curve with many peaks (
893:
342:
of a filter at a particular wavelength of light is defined as
29:
415:
depending upon the application. They were standardized for
928:. IDEX Optics & Photonics Marketplace. Archived from
762:
Polarized filters are also used to view certain types of
632:", without qualification, would be understood to be an
348:
305:Also in general, light which is not transmitted is
60:. Unsourced material may be challenged and removed.
493:The basic scientific instrument of this type is a
370:
27:Filters which selectively transmit specific colors
607:(OD) of the filter, which is the negative of the
290:materials can work as an optical filter, with an
434:There are now many absorptive filters made from
228:Optical filters are commonly used in photography
178:of filters are completely described by their
8:
955:"Datasheets on UV pass and bandpass filters"
734:. They are often made of materials such as
158:, usually implemented as a glass plane or
356:
347:
321:, interference filters, or metal meshes,
120:Learn how and when to remove this message
482:They can be used in devices such as the
399:but now usually a thermoplastic such as
881:
423:in the early 20th century, and also by
651:Examples of band-pass filters are the
471:Dichroic filters use the principle of
7:
726:Another kind of optical filter is a
197:. Many optical filters are used for
58:adding citations to reliable sources
329:much of the non-transmitted light.
201:imaging and are manufactured to be
386:of the filter at that wavelength.
25:
571:to unwanted near-infrared light.
509:wavelength division multiplexing
34:
45:needs additional citations for
1:
684:Guided-mode resonance filters
147:is a device that selectively
990:Dutch Open Telescope website
601:Neutral density (ND) filters
371:{\displaystyle -\log _{10}T}
753:black-and-white photography
505:telecommunications networks
234:instruments, and to colour
1097:
1054:shodhganga.inflibnet.ac.in
840:Filter (signal processing)
710:Metal mesh optical filters
707:
657:Fabry–Pérot interferometer
593:
495:Fabry–Pérot interferometer
453:
249:fluorescence spectroscopy
923:"How to Select a Filter"
613:transmission coefficient
553:incandescent light bulbs
545:Infrared cut-off filters
294:spectrum, and also as a
669:Swedish Solar Telescope
382:is the (dimensionless)
245:fluorescence microscopy
189:filter; then there are
138:neutral-density filters
596:neutral-density filter
372:
140:
802:A wedge filter is an
524:Monochromatic filters
373:
135:
965:on February 14, 2014
820:Anti-aliasing filter
757:specular reflections
665:Dutch Open Telescope
539:infrared photography
346:
255:Photographic filters
170:in the bulk or have
54:improve this article
935:on 16 November 2018
855:Photographic filter
825:Astronomical filter
561:overhead projectors
259:transmission curves
166:, which are either
1017:"SST CRISP images"
860:Photometric system
845:Filter fluorometer
830:Atomic line filter
778:puts out visible,
704:Metal mesh filters
427:manufacturers for
368:
180:frequency response
176:optical properties
141:
959:accuteoptical.com
738:and are used for
634:electronic filter
444:organic compounds
438:to which various
300:emission spectrum
276:spectrophotometer
130:
129:
122:
104:
16:(Redirected from
1088:
1065:
1064:
1062:
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1043:
1037:
1036:
1034:
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1023:. Archived from
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1006:
1005:
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1001:
992:. Archived from
986:"DOT tomography"
981:
975:
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961:. Archived from
951:
945:
944:
942:
940:
934:
927:
919:
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716:metal mesh grids
609:common logarithm
466:optical coatings
462:dichroic filters
381:
377:
375:
374:
369:
361:
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205:; some used for
195:dichroic filters
125:
118:
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69:"Optical filter"
62:
38:
30:
21:
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1081:Optical filters
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1015:Löfdahl, Mats.
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794:is working on.
788:welding helmets
772:
724:
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642:
630:low pass filter
625:
605:optical density
598:
592:
590:Neutral density
577:
532:
521:
458:
456:Dichroic filter
452:
450:Dichroic filter
392:
379:
352:
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339:Optical Density
268:
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63:
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51:
39:
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15:
12:
11:
5:
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1027:on 15 May 2011
1007:
996:on 26 May 2011
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708:Main article:
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661:spectral lines
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617:depth of field
594:Main article:
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484:dichroic prism
454:Main article:
451:
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367:
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313:refers to the
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236:stage lighting
174:coatings. The
162:device in the
145:optical filter
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984:Rutten, Rob.
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865:Rugate filter
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690:notch filters
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519:Monochromatic
518:
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511:on long-haul
510:
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460:Alternately,
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409:polycarbonate
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384:transmittance
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334:dimensionless
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207:light sources
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154:of different
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136:Coloured and
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113:
110:December 2009
102:
99:
95:
92:
88:
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81:
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74:
71: –
70:
66:
65:Find sources:
59:
55:
49:
48:
43:This article
41:
37:
32:
31:
19:
1057:. Retrieved
1053:
1041:
1029:. Retrieved
1025:the original
1020:
1010:
998:. Retrieved
994:the original
989:
979:
969:November 19,
967:. Retrieved
963:the original
958:
949:
937:. Retrieved
930:the original
917:
901:
884:
801:
798:Wedge filter
792:
773:
761:
732:polarization
725:
713:
698:polarization
687:
678:
650:
643:
626:
599:
584:
578:
543:
536:
533:
522:
513:optic fibers
499:
492:
481:
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473:interference
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417:photographic
393:
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296:light source
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191:interference
184:
172:interference
164:optical path
144:
142:
116:
107:
97:
90:
83:
76:
64:
52:Please help
47:verification
44:
18:Light filter
1047:"CHAPTER-2"
1021:SST website
939:15 November
870:Warm filter
850:Lyot filter
784:ultraviolet
770:Arc welding
764:stereograms
755:to control
744:photography
653:Lyot filter
580:Ultraviolet
575:Ultraviolet
565:solid state
315:attenuation
288:fluorescent
266:Measurement
220:, that is,
218:wavelengths
211:translucent
203:transparent
156:wavelengths
1059:3 November
876:References
776:arc source
740:sunglasses
390:Absorptive
311:absorbance
298:, with an
292:absorption
282:, and the
280:non-linear
187:absorptive
80:newspapers
808:intensity
728:polarizer
722:Polarizer
675:Shortpass
640:Band-pass
555:(such as
507:that use
440:inorganic
425:color gel
413:polyester
363:
350:−
240:astronomy
149:transmits
1075:Category
814:See also
780:infrared
736:Polaroid
655:and the
646:Ångström
623:Longpass
530:Infrared
307:absorbed
272:measured
694:grating
611:of the
569:sensors
549:visible
501:Etalons
429:theater
421:Wratten
419:use by
405:acrylic
401:acetate
397:gelatin
327:scatter
323:reflect
319:mirrors
232:optical
222:colours
209:can be
199:optical
160:plastic
94:scholar
1031:24 May
1000:24 May
748:angler
663:. The
488:camera
378:where
96:
89:
82:
75:
67:
1050:(PDF)
933:(PDF)
926:(PDF)
557:slide
486:of a
436:glass
431:use.
411:, or
332:The (
274:by a
238:. In
152:light
101:JSTOR
87:books
1061:2023
1033:2011
1002:2011
971:2019
941:2018
782:and
742:and
667:and
559:and
247:and
168:dyed
73:news
910:PDF
894:PDF
774:An
442:or
354:log
325:or
193:or
143:An
56:by
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