JPH0973006A - Color resolving optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a double image which is formed by reflected light from a dichroic surface of a first prism and reflected light from an incident surface of a second prism after passing through the dichroic surface, in a three color resolving optical system. SOLUTION: Three color resolving optical system is constituted by joining a sharp cutoff filter 150 onto a clichroic surface 112 of a first prism 110. The blue color component of the light passing through the dichroic surface 112 is absorbed by a filter 150, but a part of the component passes it through. The transmitted blue color component reflects on an incident plane of a second prism 120 and is made incident again to the filter 150 through which it is absorbed again. Thus, the blue color component of the light which passes through the dichroic surface 112 is sufficiently absorbed during the transmission process to the light-emitting surface 110a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color separation optical system that splits incident light into light of three colors having different wavelengths.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional color separation optical system has a first dichroic surface 12 for reflecting blue light.
The second and third prisms 20 and 30 are different from the prism 10.
The cemented prism of No. 1 is arranged via the air layer 40, and the dichroic surface 42 for reflecting red light is provided on the cemented surface of the cemented prism. Then, the color separation optical system configured as described above separates the incident light beam into blue light, red light, and green light in order. In addition, each prism 10, 2
Trimming filters 11, 21, and 31 for correcting the spectral characteristics are joined to the exit surfaces of 0 and 30.

[0003]

As described above, the dichroic surface 12 has a function of reflecting blue light,
The actual spectral transmittance is as shown in FIG. 5, and light in the wavelength range indicated by hatching in the figure is attenuated but is transmitted through the dichroic surface 12. The light thus transmitted is reflected by the incident surface of the second prism 20, and then again passes through the dichroic surface 12 and enters the first prism 10. The incident light is reflected by the incident surface of the first prism 10 and emitted from the exit surface to the outside of the prism system. As a result,
From the exit surface of the first prism 10, the dichroic surface 1
The normal light reflected by 2 and the ghost light reflected by the incident surface of the second prism are emitted in an overlapping manner, and as a result, B
The channel had the drawback of detecting double images.

The present invention has been made to solve such a problem, and its object is to improve the quality of a detected image by removing the ghost light detected due to such a cause. It is in.

[0005]

Therefore, a color separation optical system according to the present invention includes a first prism having a first dichroic surface that reflects blue light and transmits red light and green light, and the first dichroic. The second prism and the third prism are bonded to each other with an air layer interposed therebetween, and the second dichroic surface that reflects the red light and transmits the green light is provided on the bonding surfaces of the second prism and the third prism. In a color separation optical system including a cemented prism, a sharp cutoff filter for further attenuating short-wavelength light of a blue component light or less transmitted through the first dichroic surface with respect to the first dichroic surface of the first prism. Are constructed by joining. In addition,
The sharp cutoff filter is a filter that absorbs light having a shorter wavelength and transmits light having a longer wavelength with a certain wavelength as a boundary.

With this arrangement, the blue component light that passes through the first dichroic surface is sharp and
As it passes through the cutoff filter, it is partially absorbed and attenuated. The light transmitted through the sharp cutoff filter is reflected by the incident surface of the second prism and then transmitted through the sharp cutoff filter again, but at this time, a part of the light is absorbed. Thus the first
The blue component light that passes through the dichroic surface is sufficiently attenuated in the process of reaching the exit surface of the first prism.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an enlarged color separation optical system. The color separation optical system 100 includes a first prism 110, a second prism 120, a third prism 130 and a sharp prism.
It is composed of a cutoff filter 150.

The first prism 110 has a dichroic surface 112 for reflecting blue light, and a sharp cutoff filter 150 is bonded to this dichroic surface 112. The dichroic surface 112
The spectral transmittance of is as shown in FIG. 5 described above.

FIG. 2 shows the sharp cutoff filter 1
The spectral transmittance of 50 is shown. The filter 150 is a yellow transmission type sharp cutoff filter,
The break wavelength is set to 480 nm. This break wavelength is a value based on JIS B 7113, and is a value obtained by taking an average value of wavelengths having a transmittance of 72% and 5%. An example of such a sharp cutoff filter is a yellow transmission sharp cutoff filter (Y-48) manufactured by HOYA.

Further, the sharp cutoff filter 1
For 50, a junction prism is arranged via an air layer 40. This cemented prism includes a second prism 120 and a third prism.
The prism 130 and the prism 130 are joined to each other, and a dichroic surface 142 for reflecting red light is provided on the joining surface.

When light is incident on the color separation optical system configured as described above, the incident light first enters the first prism 110 and, based on the spectral transmittance shown in FIG. Is reflected by the dichroic surface 112. The reflected light is totally reflected by the incident surface of the first prism 110 and then emitted as normal light from the exit surface 110a.
It is taken out as the light of the channel.

On the other hand, the transmitted light of the dichroic surface 112 includes the light in the wavelength range shown by the hatching in FIG. 5 among the light of the blue component, and this transmitted light is the sharp cutoff filter 150. Incident on.

FIG. 3 shows the spectral transmittance curve (solid line) of the dichroic surface 112 and the sharp cutoff filter 1.
The spectral transmittance curve of 50 (broken line) is shown in an overlapping manner.
As can be seen from FIG. 3, of the blue component light (shown by hatching) transmitted through the dichroic surface 112, most of the light in the area shown by cross hatching is transmitted through the sharp cutoff filter 150. Be absorbed.

The light in the hatched area remaining in FIG. 3 is the light of the blue component that cannot be completely absorbed by the sharp cutoff filter 150, and this light is the air layer 40.
After being reflected by the incident surface of the second prism 120 via the, the light enters the sharp cutoff filter 150 again.
And, when it permeates, a part thereof is further absorbed. In this way, the blue component light is sufficiently attenuated by passing through the sharp cutoff filter 150 twice.
The light of the blue component attenuated in this way is also reflected by the first prism 1
After being totally reflected by the incident surface of 10, the ghost light is emitted from the exit surface 110a, but this ghost light is sufficiently attenuated as compared with the conventional case of FIG. 4, and a double image as in the conventional case is generated. Can be sufficiently suppressed.

On the other hand, the first prism 110 and the sharp
The second prism 1 is transmitted through the cutoff filter 150.
Of the light that has entered the inside 20, the light of the red component is reflected by the dichroic surface 142, then exits from the exit surface 120a, and is extracted as R channel light.

The green component light that has passed through the dichroic surface 142 travels straight and is emitted from the exit surface 130a of the third prism 130 and is extracted as G channel light.

The color separation optical system 100 thus separates the incident light into blue light, red light and green light.

Further, in the conventional color separation optical system shown in FIG. 4, the exit surfaces 2 of the second prism 20 and the third prism 30.
Although the trimming filters 21 and 31 for removing the blue component light mainly transmitted through the dichroic surface 112 are provided in the first and the third positions, the sharp cutoff
By providing the filter 150, the trimming filter 2
1, 1 and 31 are unnecessary, which can contribute to the reduction of the number of parts.

Although the sharp cutoff filter 150 is illustrated as a plane parallel plate in the above-described embodiments, the spectral transmission characteristics of the filter 150 can be adjusted by using, for example, a wedge type filter.

The sharp cutoff filter 1
The break wavelength of 50 is illustrated as 480 nm, but the break wavelength is not limited to this value, and the break wavelength is 460 nm to
The sharp cutoff filter 150 having a range of about 520 nm can be appropriately selected and used according to the applied optical system.

[0021]

As described above, the color separation optical system according to the present invention attenuates the dichroic surface of the first prism with respect to the short wavelength light of the blue component light or less transmitted through the first dichroic surface. Since the sharp cut-off filter is joined, the blue component light transmitted through the dichroic surface of the first prism and the blue component light reflected by the second prism and incident on the first prism again,
It can be sufficiently attenuated during the propagation process to reach the exit surface of the first prism, and the detected image quality can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a color separation optical system according to the present embodiment. It should be noted that, in the following figures, the air gap interval is enlarged and shown for the sake of convenience for easy visual observation.

FIG. 2 is a graph showing the spectral transmittance of a sharp cutoff filter used in the color separation optical system of FIG.

FIG. 3 is a graph showing the spectral transmittance curve shown in FIG. 2 and the spectral transmittance curve shown in FIG. 5 in an overlapping manner.

FIG. 4 is a configuration diagram showing a conventional color separation optical system.

5 is a graph showing the spectral transmittance of a dichroic surface for reflecting blue light in the color separation optical system of FIG.

[Explanation of symbols]

100 ... Color separation optical system, 110 ... First prism, 120
... second prism, 130 ... third prism, 150 ... sharp cutoff filter.

Claims (1)

[Claims] 1. A first prism having a first dichroic surface that reflects blue light and transmits red light and green light; and a second prism that is disposed between the first dichroic surface and an air layer. And the third prism are joined,
In a color separation optical system including a cemented prism having a second dichroic surface that reflects red light and transmits green light on the mutual cemented surfaces, the color separated optical system further comprises: A color separation optical system characterized in that a sharp cutoff filter for attenuating short-wavelength light of a blue component or less transmitted through the first dichroic surface is joined to the first dichroic surface.