SU1205093A1 - Correcting filter - Google Patents

Description

The invention relates to interference filters used to correct the spectral characteristics of sources of light; p} in photometry and color television.

The purpose of the invention is to simplify the design of the coating, as well as to reduce the light loss by reducing the reflection coefficient in the working range of the spectrum. FIG. Figure 1 shows schematically the design of the corrective filter; in fig. 2 - the dependence of the transmittance T on the wavelength. in fig. 3 shows a variant of the filter in which the coating is deposited on the substrate in the form of separate areas.

Corrective filter consists of a transparent substrate 1, on which are deposited 2 tri-sulphurous antimony and a layer 3 of polymethyl methacrylate.

The optical thickness of the three-sulfur antimony layer is A a / 2, where I is the long-wave boundary of the working area.

Each point of the image, proposed by a color television camera, gives a circle on the correctness of the correcting filter, the measures of which for various cameras lie in the range of 18-25 mm. Therefore, if about

filter spectrum, (650-750 nm). This layer

deposited on a substrate in the form of separate parts-25 of the surface of the filter alternation

covered areas and uncovered areas so that within one circle from the area of the covered areas to the area of the circle is consistent and does not depend on the position of the circle on the surface of the filter, then. By varying this ratio, you can change the spacing characteristic of the filter. For a filter with a required spectral characteristic, the ratio of uncovered areas to the area of the entire working surface

thirty

covered and uncovered areas, that within the same area of the covered area the circle is consistent and does not depend on the circle on the surface of the filter specified ratio, it is also possible to filter the filter with the required characteristics

 ,

the ratio of the area of the uncovered areas to the surface area of the substrate, performed, for example, from glass of brand K 8, paBHotu- where o is the specified transmittance of the filter and i) „p is the transmittance of the coating at the wavelength | (J, is the short-wavelength boundary of the working region of the filter spectrum 380-450 nm). Such a filter provides a linear dependence of the transmittance on the wavelength; with L = 400 nm, T = 20 ± 5% and those substrates should be chosen

at 91 - 700 nm, T - 80 t 5% (curve 4, fig 2).

Other transmittance values can be obtained by adding neutral attenuators to the filter, made, for example, on the basis of thin titanium layers.

To reduce the reflection coefficient of the coating in the wavelength range of 400-550 nm, as well as to increase the mechanical strength of the filter, a layer of three-sulfur antimony is covered with a layer of polymethyl methacrylate, the optical thickness of which is (0.5-0.8) l / 4. The spectral characteristic of such a filter corresponds to curve 5 in FIG. 2

The action of the proposed filter is based on the property of a three-sulfur antimony layer with an optical thickness f IZ. provide linear energy coefficient40

In this case, the prop ratio is written as

TFY-0-0% 1 - by

where t

mean

45

50

uncovered transfer rate.

From relations (1–3) in the wavelength range (y, LS is a linear relationship, with HTq, (fl) La (curve 6, FIG.

The proposed corrective provides in the working interval the spectral dependence of the transmission coefficient and is less sweaty with Fresnel reflection

12050932

transmission band T (N) in the range of lengths, waves C, Al) This is due to the interference with it and the selective absorption in a thin layer acting simultaneously. This property is confirmed by the spectral characteristic of a layer of three-sulfur antimony with an optical thickness of 350 nm (curve 4, fig. 2). From the graph it follows that the three-sulfur layer we have a linear spectral dependence,

Q which in the wavelength interval (;, ya) is described by the equation

Cx)

 Aa-Av

ate -) + p. (1)

where b q - transmittance with optical thickness X а / 2.

At the same time, the transmission coefficient of H. (H) -20 + 4%.

The filter works as follows.

Each point of the image offered by a color television camera gives a circle on the surface of the correcting filter, the dimensions of which for various cameras are in the range of 18-25 mm. Therefore, if

  filter surface alternation

covered areas and uncovered areas in such a way that, within one circle, the ratio of the area of the covered areas to the area of the circle is consistent and does not depend on the position of the circle on the filter surface, then. vary this ratio, you can change the spectral characteristic of the filter. To obtain a filter with the required spectral characteristic, the ratio of uncovered areas to the area of the entire working surface of the substrate should be chosen

 ,

and should choose

(2)

40

In this case, the filter transmittance is written as

TFY-0-0% 1 - poal, (3)

where t

mean

uncoated substrate transmittance.

From relations (1-3), it follows that the filter in the wavelength range (r., Ls,) has a linear relationship, with () to HTq, (fl) La (curve 6, Fig. 2).

The proposed correction filter provides, in the working range, a linear spectral dependence of the transmittance and has lower losses associated with the Fresnel reflection.

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60

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20

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Editor A. Ogar

Compiled by P. Yakovlev Tehred L. Mikesh

Order 8525/48 Circulation 525

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Branch SHSh T1atent, Uzhgorod, st. Project, 4

//2.2

Corrector. A. Tsko

Subscription

Claims (2)

1. CORRECTIVE FILTER, consisting of a substrate transparent in the working range of the spectrum limited by wavelengths fl, and A, where ft _K and A are the short-wave and long-wave boundaries, respectively, with an interference coating deposited on its surface, characterized in that, for the purpose of Nia coating design simplification, the latter is formed of antimony trisulfide layer with an optical thickness equal to a / 2 disposed on the substrate in the form of individual portions, wherein the ratio of the uncoated areas to the area of the entire surface of the substrate is equal to -? , where is the specified transmittance of the filter and is the transmittance of the coating at a wavelength of A _to .. 2. The filter according to claim 1, characterized in that, in order to reduce light loss by reducing the reflection coefficient in the working range of the spectrum, a layer of polymethyl methacrylate with an optical thickness of (0.5-0.8) A _k / 4 is applied to the interference coating . Fi.13