JP2006091482A - Ceramics lens for optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a lens with resolution suited for an optical device by using a polycrystalline structure translucent ceramics. <P>SOLUTION: The ceramics lens is constructed by polishing the translucent ceramics of which the particle size is 125 μm or less as a glass material, out of the polycrystalline structure translucent ceramics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a small high-performance optical lens group mainly used in a small image pickup device such as a digital camera.

In recent years, compact and high-performance zoom lenses have been used in optical devices such as digital still cameras and video projectors.
A combination lens such as a zoom lens of this optical device is required to be small and have high resolution.
In addition, translucent ceramics have been developed today, and these translucent ceramics have a higher refractive index than optical glass, and the values of hardness and bending strength are higher than those of optical glass. Lenses suitable for reduction in thickness and thickness have been manufactured.

Since this translucent ceramic has a high refractive index and high hardness and bending strength, it is optimal for miniaturizing the optical system of an optical device if it is used as a lens.
However, since this translucent ceramic has a difference in transmission characteristics in the visible wavelength range, it appears slightly yellowish, and there are bubbles called voids at the crystal grain interface. The lens has a problem that the sharpness of the image is slightly lower than that of the optical glass lens.

However, the present applicant has filed an application for specifying a combination condition as a zoom lens for a digital still camera having a small size and high functionality, which is an inexpensive combination lens with a small number of lenses constituting the zoom lens (for example, patent document) 1) was performed.
In such an optical device lens, if a ceramic lens is arranged in the vicinity of the position where the principal ray of each image point overlaps, the position at which the light beam of each image point formed on the image plane passes through the ceramic lens can be determined. By making it common, it is possible to reduce the difference in influence such as coloring or flare caused by the ceramic lens, and it becomes possible to use the ceramic lens in a lens device for optical equipment.
JP 2003-057542 A

Since the ceramic lens can have a high refractive index and can have a high hardness and bending strength, it can exhibit advantages superior to an optical glass lens as a lens for optical devices.
However, the resolution of the lens differs depending on the particle diameter of the translucent ceramic used for the lens material, and some lenses are not suitable as lenses for optical devices.
The present invention is to provide a ceramic lens suitable for an optical device by suppressing the disadvantages of such a ceramic lens.

The present invention provides a ceramic lens obtained by polishing a light-transmitting ceramic having a particle size of 125 μm or less among the light-transmitting ceramic having a polycrystalline structure as a glass material, and preferably has a particle diameter of 85 μm or less. Photoceramics are used as a glass material.
As described above, if a translucent ceramic having a particle diameter of 125 μm or less is used as a glass material, the MTF value can be set to 70% or more for a 30 line pair / mm sine wave grating, and the particle diameter is 85 μm or less. If the translucent ceramic is made of glass, the MTF value can be 80% or more for a sine wave grating of 30 line pairs / mm.

The spectral transmittance of the ceramic lens is preferably 72% or more in the range of 420 nm to 700 nm.
As described above, when the spectral transmittance is set to 72% or more in the range of 420 nm to 700 nm, an image can be formed by transmitting light of each wavelength in the visible light region.

Further, this ceramic lens is made of a translucent ceramic having a refractive index of 2.0 or more as a glass material.
Thus, since the refractive index is 2.0 or more, a lens having a higher refractive index than that of optical glass can be obtained.

  The ceramic lens for an optical device according to the present invention is made of a translucent ceramic having a particle diameter of 125 μm or less among translucent ceramics having a polycrystalline structure, and is a sine wave of 30 line pairs / mm. The MTF value of the grating has a resolution of 70% or more, and a high-resolution lens suitable for the optical apparatus can be obtained.

In addition, the spectral transmittance is set to 72% or more in the range of 420 to 700 nanometers, and the visible light transmittance is ensured and used as a lens for imaging devices such as cameras and projection devices such as projectors. Is something that can be done.
If the ceramic lens has a refractive index of 2.0 or more, a lens optical system having a small size and high performance can be formed as a lens having a higher refractive index than a lens made of general optical glass.

  The ceramic lens according to the present invention is made by translucent ceramics having a refractive index of 2.0 or more and a particle diameter of 125 μm or less as a glass material by cutting, roughening, sanding, polishing, etc., and has a spectral transmittance of 420. In the range of nanometers to 700 nanometers, a ceramic lens of 72% or more is obtained.

The present invention uses translucent ceramics having a refractive index with respect to d-line of 2.08 and an Abbe number of 30.4, and is formed into a rough shape by roughing and finished by sanding. Then, polishing and centering were performed to prepare a concave meniscus lens having a thickness of 0.4 mm and a diameter of 4 mm.
The translucent ceramic has an optical characteristic of linear transmittance of about 70 percent transmittance around 400 nm, about 95 percent transmittance between 450 nm and 700 nm, It has a yellowish tint.

And when this ceramic lens is combined with another optical glass lens to make a zoom lens for a digital still camera, it maintains its sharpness and exhibits the same performance as a conventional optical glass lens, but is stronger than the optical glass lens. It was possible to make it a high lens.
Further, when the ceramic lens was produced, the translucent ceramic particles having a particle diameter of 70 μm, 120 μm, and 150 μm were roughened and polished, respectively, to obtain an optical lens.

  Then, MTF (modulation transfer function) measurement was performed on the ceramic lenses having different particle diameters using a sine wave grating in which 30 lines were drawn per millimeter, and the results were as shown in Table 1.

As a result of simulation, it has been found that if the particle diameter is about 125 μm, the MTF value can be 70% or more, and if the particle diameter is about 85 μm, the MTF value can be 80% or more.
In addition, the current minimum particle diameter of translucent ceramics is about 15 μm to 20 μm.

  ADVANTAGE OF THE INVENTION According to this invention, the lens apparatus for optical apparatuses which is small and durable can be manufactured, without reducing a picture quality, using a ceramic lens.

Claims (3)

  A ceramic lens obtained by polishing a light-transmitting ceramic having a particle diameter of 125 μm or less among a light-transmitting ceramic having a polycrystalline structure as a glass material.   2. The ceramic lens according to claim 1, wherein the spectral transmittance is 72% or more in a range of 420 nm to 700 nm.   The ceramic lens according to claim 1 or 2, wherein a translucent ceramic having a refractive index of 2.0 or more is used as a glass material.