JPS62262819A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain a projected image having an excellent resolution and a high visibility by placing an optical filter for making a light beam of a specific wavelength area pass through partially, in the front part, the rear part, or between lenses, of a lens system constituted of plural lens elements. CONSTITUTION:An optical filter 3 is installed in front of the first lens L1, and a focusing adjustment is executed by rotating and sliding an inner lens barrel 2 and adjusting an air interval between the second lens L2 and the third lens L3. The part to which hatching is performed, of the optical filter 3 shows a filter part 3a which is colored or on which a thin film has been formed, for selecting and filtering alight beam. Although it is allowed to attach the filter to the whole surface, if it is executed, the passing quantity of a light beam decreases, and lightness of an image surface falls, therefore, it is undersirable. In general, as for a light beam for passing through the outside peripheral area of the lens, its aberration becomes large, therefore, it is effective for reducing a color bleeding of an image to cut off an unnecessary light beam for passing through the outside peripheral area, and a fall of lightness of the image surface can be made as small as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a projection lens used when enlarging and projecting images on a cathode ray tube (CRT) surface onto a screen.

Conventional technology The refractive index of light differs depending on the wavelength even in a raw material, and when light travels through a material, a phenomenon called wavelength dispersion appears. Visible light is light with a wavelength of approximately 350 nm to 700 nm, and when an image is formed using a lens,
Wavelength dispersion occurs and color fringing occurs in the image on the screen. This is because the various colored lights included in the visible light range are not focused on the same position on the screen surface.

This is called chromatic aberration of the lens. For photographic lenses, etc.
We create lenses using materials with different refractive index and wavelength dispersion,
A lens system is constructed by cleverly combining these elements to reduce chromatic aberration within a practically acceptable range. Such lenses are called achromatic lenses.

The projection lens of short-tube projection color televisions uses a projection lens to enlarge and project CRT images onto a screen.
Generally, achromatic lenses are used. FIG. 6 shows an example of a conventionally used projection lens. (Nikkei Mechanical, October 1983 issue) The reason why achromatic lenses are not generally used in projection TVs is that the monochromatic light emitted by three tubes (red, green, and blue) (IRT images are transmitted using three projection lenses). In projection televisions that project color images onto the same screen, each projection lens is used to project nearly monochromatic light with a relatively narrow wavelength range compared to natural light. Because the band is narrow, there is some wavelength-dependent dispersion, but it is not a very large amount.Also, such lenses are used for images of an acceptable level.

In recent years, the demand for televisions has been trending toward larger screens, and the popularity of projection televisions has also rapidly increased. In addition, as screens become larger, the demand for higher image quality is increasing, and even higher quality images are desired due to the development of high-definition televisions. ○ Problems that the invention aims to solve Image quality In order to improve the image quality, it is important to obtain a clear image, and the contours of the image need to be expressed sharply. .

In order to obtain clear images in a projection television, the color fringing caused by the projection lens as described above must be reduced as much as possible, and eliminating chromatic aberration of the lens is an important issue. If there is color bleeding, you will not be able to obtain clear images with excellent resolution. As mentioned above, in short-tube projection color televisions, each lens has a narrow wavelength range of light, so the occurrence of chromatic aberration is relatively small, and although achromatic lenses are not used, Although the emission wavelength range of the CRT6 . For example, if we take a green-emitting CRT as an example, it has a distribution as shown in FIG. Therefore, when such light is projected through a projection lens, a considerable amount of chromatic aberration occurs, causing the edges of the image to appear colored. In order to obtain even higher quality images, such color fringing must also be removed. One way to remove color fringing is to use achromatic lenses, but
Achromatic lenses require the addition of multiple lens elements made of expensive glass material, which increases costs. Another method is to attenuate unnecessary wavelength components by passing the light from the CRT through an optical filter when entering or exiting the lens, and projecting the light into near-monochromatic light with a narrow wavelength range. There is. In this way, a sharp image with less color blur can be obtained. Taking FIG. 4 as an example, a filter may be used to block the light of the B, C, and D components in the figure and to pass the light of the A component.

Of course, which band of light to pass through the filter will differ depending on the target light.

In view of the above points, the present invention provides a projection lens using an inexpensive and effective optical filter.

Means for Solving the Invention In order to solve the above-mentioned problems, the projection lens of the present invention has a coloring or dimensioning that allows light in a specific wavelength range to pass through immediately before, immediately after, or between the lenses of the lens system. By placing an optical filter with a thin film formed on it, or by applying the above-mentioned filter function to the lens element itself, unnecessary light is attenuated and shaped into light with a narrow spectral width, thereby reducing color fringing. As a result, a clear and clear projected image can be obtained.

When a projected image is formed using a working projection lens, color fringing appears at the periphery of the image due to the chromatic aberration of the lens, reducing the sharpness of the image. This is because the projection light contains light of various wavelength components, and if it were a single wavelength light, this phenomenon would not occur.

The present invention is based on −'f! An optical filter that passes only light in a constant wavelength range is used to block unnecessary light and reduce color fringing in images. An optical filter having such a function is applied to the lens element itself by coloring or forming a thin film, or it is applied to a colorless transparent plate or film.

Example Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a caster lens employing an embodiment of the present invention. In the drawings, reference numeral 1 denotes an outer lens barrel, and an inner lens barrel 2 is housed in its cavity so as to be movable back and forth and rotatable. Band-shaped protrusions 2a and 2b are formed at the front and rear of the outer circumference of the inner barrel 2, and are in sliding contact with the inner circumferential wall of the cavity of the outer barrel 1.
The inner lens barrel 2 and the inner lens barrel 2 are designed to slide and rotate in a good fitted state.
1. Second lens L2. A third lens L3 is attached. An optical filter 3 is attached in front of the twisted second lens L2.Focusing adjustment is performed by rotating and sliding the inner lens barrel 2 to adjust the air distance between the second lens L2 and the third lens L3. It is done by adjusting and subtracting. FIG. 2 is a front view of the optical filter 3.

The hatched portion represents a filter portion 3a in which a colored thin film is formed from 1 to 1 for selectively filtering light. It would be possible to apply a filter to the entire surface, but this would reduce the amount of light passing through and reduce the brightness of the image plane, which is not ideal. In general, light that passes through the outer periphery of a lens has greater aberration, so it is effective for blocking unnecessary light that passes through the outer periphery and reducing color fringing in images.
Decrease in brightness on the image plane can also be minimized. In the embodiment described above, the filter section 3a is applied to the entire outer peripheral area, but in order to reduce the reduction in brightness of the image plane, it is better to make the area of the filter section a little smaller6. This is another embodiment of the present invention. Filter portions 3a are provided concentrically, and a non-filter portion is provided between them to increase the amount of light passing through. As the number of non-filter parts increases, color fringing increases, so it is important to find more optimal values for the area, shape, and arrangement of the filter parts in consideration of image quality. In the second explanation, the filter portion is formed on a colorless transparent glass plate, plastic plate, etc., but it is also possible to form the filter function on the lens element itself. By doing this, the number of parts can be reduced, the assembly process can be shortened, and the lens can be made simpler.

Effects of the Invention As described above, the present invention achieves this effect by attaching an optical filter provided with a filter section that allows light in a specific wavelength range to pass through the lens system, or by applying it to the lens lens itself. The filter section attenuates unnecessary light, making it more like monochromatic light, reducing color blurring in images due to chromatic aberration of the projection lens [2. It is possible to obtain a projected image with excellent resolution and high clarity. .

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a projection lens equipped with an optical filter according to an embodiment of the present invention, Fig. 2 is a front view showing an optical filter of the present invention in which a filter portion is formed in the outer circumferential area, and Fig. 3 is a cross-sectional view of a projection lens equipped with an optical filter in the outer circumferential area. A filter section is formed concentrically in 1 to 10. Front view showing other embodiments of the light filter. Figure 4 is a spectrum diagram of the light emitted by a green-emitting CRT, and Figure 5 is a diagram of a conventional projection lens. It is a sectional view showing an example. 1... Outer barrel, 2... Mountain... Inner barrel, S...
・Optical filter, L1 river...second run, L2 river...second
Lens, L3...Third lens, 3a...Middle/filter forming part.

Claims (4)

[Claims] (1) An optical filter, which is a colorless transparent plate or film that partially passes light in a specific wavelength range, is installed at the front and rear of a lens system consisting of multiple lens elements. Or a projection lens characterized by being arranged between lenses. (2) Filters have patterns such as stripes, lattices, dispersed dots, radials, concentric circles, etc. that are selectively colored with translucent color or formed with a thin film, and the colored portions or thin film formed portions are non-contact. 2. The projection lens according to claim 1, further comprising a forming portion. (3) Coloring or forming a thin film that allows light in a specific wavelength range to pass through is partially applied to any lens element in a lens system made up of multiple lens elements. A projection lens according to claim 2. (4) Lenses are selectively coated with light-transmitting coloring or thin film formation in patterns such as stripes, lattices, dispersed dots, radials, and concentric circles, with colored areas or thin film forming areas and non-colored areas. 4. The projection lens according to claim 3, further comprising a projection lens.