JPH02118501A - Lens for projection type television - Google Patents

Abstract

PURPOSE:To shut off the spuriousness of a phosphor and to eliminate chromatic aberrations so as to greatly improve focusing performance by forming multilayered films which are varied in transmittance by wavelengths of rays on one face of a constituting lens element. CONSTITUTION:The focusing performance of the projection type television is most largely affected by the focusing property of the green enlarged image with which the specific visual sensitivity is max. The red and blue spuriousness, however, exists in the actual light emission of the phosphor with respect to the green reference wavelength. The multilayered films (multilayered filters) which are varied in the transmittance by the wavelengths of rays and have the transmittance of wavelength selectivity are, thereupon, formed of the coating films on the incident surface of the 3rd lens 3 which constitutes the lens system. The spuriousness of the phosphor is shut off in this way and the chromatic aberrations are eliminated, by which the focusing performance is greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of Niratojo] The present invention relates to a projection lens suitable for a projection television apparatus.

[Conventional technology]

In general, in projection TVs, the brightness of the projection tube that is the light source is high (and the contrast of the enlarged image on the screen is significantly reduced due to unnecessary light generated by reflection from each lens element. This is countered by coating the lens element with an anti-reflection film. For example, examples related to this type of coating include JP-A-60-126601 and tF!j JP-A-60-11.
Publication No. 704 and the like can be mentioned.

[Problem that the invention seeks to solve]

In the above-mentioned prior art projection television lenses, a large number of anti-reflection films (referred to as below C coatings) are used to provide light in the visible range (580 nm to 740 nm).
The focus was only on improving contrast by reducing unnecessary reflected light by increasing transmittance, but no consideration was given to improving focus. Conventionally, the phosphor of the green projection tube, which controls the brightness of the TV, has a main wavelength of 545rLm, as well as a red spurious signal in the evening, as shown in Figure 7. This caused chromatic aberrations to occur on the imaging plane, making it impossible to obtain high-n images. Therefore, an object of the present invention is to improve focusing performance by coating.

[Means for solving problems]

The above purpose is to provide a high WI fine resolution without chromatic aberration that can block the sources of spurious blue and red by applying a multilayer coating with filter properties to at least one surface of each lens element of the lens that enlarges and projects a green image. It becomes possible to obtain a clear image. Here, the light rays that enter the lens elements constituting the projection lens do not enter the lens surface under pressure perpendicularly. For this reason, a multilayer coating with a film thickness optimized for vertically incident light will not be able to obtain the desired filter characteristics if the light rays are incident obliquely, and the transmittance will vary depending on each part of the lens. This appears as uneven brightness. For this reason, when combined with image light of two other colors (blue and red), color unevenness appears. Therefore, by setting the layer thickness of this multilayer film to an optimum value at each portion of the lens surface, it becomes possible to suppress the aforementioned color unevenness, block spurious waves, and reduce color convergence.

[Effect]

In general, the focus performance of a projection television is most greatly influenced by the focus performance of the green enlarged image, which has the largest relative luminosity among the five enlarged images of red, blue, and green. Therefore, when designing the lens, we focused on the g-line (546
, 1 door) is taken as the fundamental wavelength. However, actual phosphors emit light at not only a single wavelength. - As shown in Fig. 7, the emission spectrum distribution of the green phosphor is as follows: In addition to the main wavelength near 540 nm, there is a first spurious near 490 nm, a second spur near 59 Q nm, and a second spurious near 620 nm. Ratio 3 spurious exists near nm. For this reason, axial and lateral chromatic aberrations occur on the screen, degrading focus performance. Here, the projection television lens of the present invention eliminates chromatic aberration by blocking the above-mentioned spurious of the phosphor with a coating film having filter properties applied to at least one surface of the lens element. Therefore, the orcus performance is greatly improved.On the other hand, regarding color unevenness, the transmittance of the filter is selected slightly in the 6th part by selecting the transmittance in the middle of the screen, and vice versa. By increasing the transmittance of light, uneven brightness over the entire screen area is reduced.

〔Example〕

Hereinafter, the present invention will be explained with reference to embodiments shown in the drawings.

FIGS. 1, 2, and 5 show that the lens device shown in %Kai No. 85070/1986 has an axial and relative chest height of 0.4.
FIG. 2 is a cross-sectional view showing which part of each lens element inside the lens a light ray emitted from an object point with a relative chest height of 0.8 passes through. In FIG. 1, a parallel plate 11 is shown for convenience of explanation. Next K Figure 4 r Figures 5 and 6 are
It shows the distribution of the incident angle of the image light incident on the object side of the lens 3.

Region ■ has an incident angle of 0 degrees to less than 10 degrees, region ■ has an incident angle of 10 degrees to less than 20 degrees, region ■ has an incident angle of 20 degrees to less than 50 degrees, and region ■ has an incident angle of 30 degrees to 40 degrees. The area V indicates an area where the incident angle is 40 degrees or more.

Here, in the present invention, the first aspect of the emission spectrum characteristics of the green phosphor shown in FIG. Second. Blocking of the fifth spurious is achieved by applying a multilayer film (hereinafter referred to as a multilayer film filter) having wavelength-selective transmittance to the lens surface (in this example, the incident surface of the third lens 3). . This eliminates chromatic aberration (and has the effect of improving focus).

Next, the characteristics of specific multilayer filters are shown in Figures 8 and 9.
As shown in the figure. The block diagram in Fig. 8 shows the characteristics of the cyan filter DF-C manufactured by HOYA (C stock). Similarly, the solid line in FIG. 9 also shows the characteristics of the EOYA filter DF-Y. In general, the cut wavelength λC of a multilayer filter is a linear function with respect to the thickness of each film constituting the multilayer filter, and as the angle of incidence θ to the multilayer filter changes, the effective film thickness l t1, In' = IrL/capθ, and the new capacitance λC' is also λC' = λC/CO! becomes θ. Characteristics other than the solid lines shown in Figure 88 are the filter characteristics necessary to achieve the same characteristics as the solid lines when light rays enter the multilayer filter at each incident angle θ (however, the characteristics at the incident angle θ = 0°) ] From this figure, it can be seen that the film thickness needs to be thin in the part where the incident angle θ of zero light operation is large.

Similarly, in Figure 89, the characteristics other than the actual characteristics are the filter characteristics necessary to obtain the same characteristics as the solid line when the light rays enter the multilayer filter at each incident angle θ (however, at the incident angle θ = 0°) characteristics). Therefore, for example, in order to improve the focusing performance at relative chest height of 0 (on-axis), the second spurious.

When the fifth spurious is reduced by a filter with the characteristics shown by the solid line in FIG. 8, the third spurious becomes 8.0 to 0.0.
Attenuates to 8%. Also, the second Sgelias is 20% to 16%.
attenuates to Similarly, in order to attenuate the first spurious, it is possible to reduce it from 40% to 2% by using a filter with the characteristics shown by the solid line in FIG. Here, the characteristics of the multilayer filter applied to the entrance surface of the fifth lens are as shown by the solid line on the optical axis, that is, θ = 0°, area I is θ = 5°, and area ■
is θ=15°, area m is θ=25°, area ■ is θ=55
Distribute the thickness of each membrane in the filter so that it has the characteristics shown in degrees. If the film thickness of each filter film at the part where the angle of incidence θ=D° is In, then in the area ■, jrL'=jn
/cos5°, b'=! in region ■! ψoz55°
It is good to say. Even when the object point is off the original axis, the thickness of the coating may be changed in each region, as shown in FIGS. 5 and 6. Figures 10 and 11 are the above-mentioned patent application filed in 1986-85.
This is the result of calculating how the MTF of 500 TV lines changes as a focus performance of the lens device shown in No. 070 by cutting off spurious. The 10th cause is Zagital, and Figure 11 is Meridional MT.
It shows about F.

Among them, 1 indicates the design value, 2 indicates the MTF when spurious 6 is completely blocked, and 3 indicates the MTF when spurious 2 and 3 are completely blocked.

Furthermore, 4 is a state in which spurious signals 1 to 5 are completely blocked,
That is, it shows the MTF in the case of zero chromatic aberration. As is clear from the figure, the reduction of chromatic aberration by the multilayer filter resulted in a significant improvement in focus performance.

Next, the brightness at the periphery of the lens differs slightly from the original characteristics of the lens due to the characteristics of the multilayer filter. A multilayer film filter designed with an incident angle θ=0° and a multilayer film filter designed with an incident angle θ=15° were incorporated into a conventional lens on the incident surface of the third lens, and the relative value of the amount of peripheral light was actually measured. As a result, as shown in FIG. 12, it became possible to slightly move the lens' original characteristics. It goes without saying that the same effect can be obtained by inserting a parallel flat plate made of glass or synthetic resin into the lens as shown in FIG. 1, and applying the multilayer filter to this surface. With K, the image brightness becomes more uniform and color unevenness can be reduced.

A method of coating a glass or synthetic resin substrate with a multilayer filter having different film thicknesses in different parts of the lens will be described below. FIG. 15 is a longitudinal sectional view showing an example of a vacuum evaporation apparatus used to carry out the coating method of the present invention. A window is provided at the center of the rotation stage 12, and the rotation axis of the stage is provided at the center of this window. Furthermore, the steamer material is placed on an extension of this shaft. When using a steam tank, the air in the vacuum chamber 17 is removed by the vacuum exhaust system 16 and the electron gun 15 is removed.
The electrons starting from are bent by the exit field and collide with the fish waste material 14. At this time, heat is generated locally and the fish waste material evaporates. At this time, the velocity of the evaporated particles accelerated by the vapor pressure V'
is generally v' when the divergence angle from the steam tank material is θ
= vcosθ. (However, V is the velocity when the evaporated particles fly out perpendicularly to the vaporization vessel material.) Therefore, the thickness of the group 7iiF film deposited within a unit time on the vapor deposition surface of the lens element 19 is as follows. It is proportional to V'. Therefore, by using the evaporation N' device having the structure described above, it becomes possible to cover each part of the lens with a multilayer filter having different film thicknesses in a relatively simple manner.

Furthermore, Fig. 14 shows that by shifting the axis of rotation of the stage mentioned above and the center of the window provided on the stage, it is possible to cover any part of the lens with a multilayer filter with different film thicknesses, centering on any point on the substrate. becomes. - On the other hand, in order to improve mass production, a mask jig 21 is placed between the 7V substrate to be evaporated and the electron gun 15 as shown in Figure 15 (α), and the window provided in this jig is Diameter: τ, and distance between jig 21 and electron gun 15: D
By optimizing , a multilayer filter with the required thickness distribution can be easily obtained.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved by using the lens shape and structure of a lens whose chromatic aberration has not been corrected due to the lens design, and by coating at least one surface of the constituent lens elements with a multilayer film having a filter effect. be.

■ Eliminates chromatic aberration and greatly improves focus by blocking spurious emissions from the phosphor.

(2) The peripheral illumination ratio can be slightly changed from its original characteristics, and the peripheral illumination ratio at any image height can be apparently increased. Therefore, the image brightness on the screen becomes more uniform, and color unevenness can be reduced.

On the other hand, with the multi-711m coating method of the present invention, a multilayer film having different film thicknesses in each part of the lens can be relatively easily realized.

[Brief explanation of drawings]

1 to 3 are longitudinal sectional views showing one embodiment of the present invention, FIGS. 4 to 6 are distribution diagrams of the angle of incidence of light rays on the lens surface, and FIG. 7 is a diagram of the green phosphor element. Emission spectrum characteristic diagram, No. 8
9 to 9 are characteristic diagrams of the filter, FIGS. 10 to 11 are MTF characteristic diagrams for the embodiments of the present invention, and FIG. 12 is a characteristic diagram showing the amount of peripheral light in the embodiments of the present invention, Factor 13 and FIG. 15 are diagrams showing an example of a vacuum type N apparatus using pressure to carry out the method of the present invention, and FIG. 14 is a diagram showing a method of coating an optical multilayer film of the present invention. 1: 1st lens 2: 2nd lens 3: 3rd lens 4: m4 lens 5: Inner barrel
6: Outer barrel 7: Bracket 8: Fluorescent surface 9: 7-eighth panel 10: Refrigerant 11: Parallel plate 12: Rotating stage 13: Evaporation particles 14: Vacuum tank material 15: Sub-gun
16: Vacuum exhaust system 17: Vacuum chamber 18:
Resistance heater 19: Lens element Fig. 5 Fig. 6 Fig. 3 Fig. 4 Fig. 7 Fig. B Fig. 9 Relative image height .2 ○4 0. f; Oδ ; O 4]

Claims (1)

[Claims] 1. A lens used in a projection television that enlarges and projects an image on a fluorescent surface of a cathode ray tube onto a screen, in which a multilayer film whose transmittance varies depending on the wavelength of the light beam is provided on at least one surface of the constituent lens element. A lens for a projection television, characterized in that the thickness of the multilayer film is non-uniform over the entire surface of the lens. 2. When the film thickness of each film constituting the multilayer film is ln (n is a natural number), ensure that the film thickness ln' of each film corresponding to the multilayer film at each part of the lens surface satisfies the following formula. The projection television lens according to claim 1. ln'=ln/cos θ where θ is the angle of incidence of light on the multilayer film, 3; it is a lens used for projection televisions that magnifies and projects the image on the fluorescent surface of a cathode ray tube onto a screen, and at least one of the constituent lens elements is parallel. 1. A projection television lens, which is a flat plate, and has a multilayer film on at least one surface of which the transmittance varies depending on the wavelength of light, and the thickness of the multilayer film is nonuniform over the entire surface of the lens. 4. When the film thickness of each film constituting the multilayer film is ln (n is a natural number), the film thickness ln' of each film corresponding to the multilayer film at each part of the lens surface satisfies the following formula. 6. The projection television lens according to claim 5. ln'=ln/cos θ where θ is the angle of incidence of the light beam to the multilayer film, 5; it is a multilayer film formed on a glass or synthetic resin substrate and consists of multiple layers having different transmittances depending on the wavelength of the light beam; The thickness of each film constituting the multilayer film is ln
(where n is a natural number), an optical multilayer film characterized in that a film thickness ln' of each film corresponding to the multiple films at each part on the substrate satisfies the following formula. ln'=ln/cosθ where θ is the angle of incidence of light rays on the multilayer film, 6, and the rotation axis of the rotatable stage on which the substrate to be deposited is placed when coating the optical multilayer film on a glass or synthetic resin substrate. A method for coating an optical multilayer film, in which a vapor deposition material is arranged on an extension line of the stage, a window is provided at the center of rotation of the stage so that the vapor deposition surface of the substrate to be vapor deposited is exposed, and vacuum vapor deposition is performed while rotating the stage. . 7. Claim 6, characterized in that the center of the window provided on the rotary stage is offset from the rotation axis of the rotary stage.
The method for coating the optical multilayer film described above. 8. The method of coating an optical multilayer film according to claim 6 and claim 7, characterized in that the evaporation area of the substrate to be evaporated is varied by appropriately selecting the opening size of a window provided on the rotary stage.