JP2023090455A - achromatic lens - Google Patents

Abstract

To provide a lens capable of offering almost zero axial chromatic aberration.SOLUTION: Red, blue, and green optical filters are used to separate light into three monochromatic light components, and a multifocal lens fabricated such that the three monochromatic light components are in focus is used.SELECTED DRAWING: Figure 2

Description

The present invention relates to a mechanism for eliminating chromatic aberration produced by telescope lenses as much as possible.

When light passes through a lens, it experiences chromatic aberration that causes color to bleed into the image.
Conventionally, in order to reduce it, an achromatic lens such as an achromatic lens or an apochromatic lens in which a plurality of lenses are superimposed has been devised, but the present invention is a method of further reducing it.

The multifocal lens 1 of FIG. 1 has an inner side 2, an intermediate side 3, and an outer side 4. When viewed from the front, the surface areas of 2, 3, and 4 are the same.
In this state, the lenses 2, 3, 4 and their optical paths 13 have different focal lengths, so they are inferior lenses.

Next, install an optical filter 8 in front of 1 to match the diameter of 1. This 8 is a filter that allows blue light with a wavelength of 450-485 nm to pass from the inside, and a green light with a wavelength of 500-565 nm in the middle. It consists of a filter through which red light with a wavelength of 625 to 780 nm passes through, and the size of the surface area of each filter seen from the front is the same as 2, 3, and 4 of lens 1.

The light passing through 8 becomes only blue light, only green light, and only red light for 2, 3, and 4, and each of them overlaps one focal point. The reason for this is that the focus of the lens is different for blue, green, and red, and the focal shifts of the three colors are calculated backward so that they are combined into one through the optical filter 8 .

Specifically, it is as follows.
5 is an optical filter that passes blue light with a wavelength of 450-485 nm; 6 is an optical filter that passes green light with a wavelength of 500-565 nm; and 7 is an optical filter that passes red light with a wavelength of 625-780 nm. Then the three color focal points 14 are as follows.
The focus of 3 is processed so that the green light 6 is aligned with the blue focus 5. The focus of 4 is processed so that the red light 7 is also aligned with the blue focus 5. This order takes into consideration the refractive index of the glass. It also facilitates the actual processing.
Blue light has a higher refractive index than the other two colors, so if it is placed on the outer circumference, the focal point becomes complicated, but if red light, which has a low refractive index, is placed on the outer circumference, the focal point is shortened. This is because it requires only simple processing.

As a result, the focus of red, blue, and green light converges to a single point to eliminate chromatic aberration.
In this state, the light near the boundary line between 9 and 10 in FIG. 2 shifts inward and the images are superimposed, and chromatic aberration of magnification becomes noticeable. Magnification chromatic aberration is a chromatic aberration that occurs on the periphery of the lens and cannot be eliminated even with the present invention.

In order to eliminate this shift of light, it is necessary to provide a light blocking ring 12 at the center of the boundary of the filter to block the shifted light.
The reason why 12 is the center of the boundary of the filter is to reduce the chromatic aberration of magnification caused by light entering from the inside of the lens.

Assuming that the distance between the filter and the lens is 0, the thickness 11 of the ring is calculated as follows.

The thickness of the shielding ring = the radius of the filter / the focal length x the thickness of the lens x 2

2, 3, and 4 have different focal lengths and should be calculated separately for each focus, but it can be said that they are not important from the values expressed by the following formulas.

Focal length ÷ lens diameter = F number

If this f-number is 1, the filter will be covered with a light blocking ring. In FIGS. 1 and 2, the focal point is set to be short for easy understanding of the focal point, but it is not desirable to cover more than half of the focal point with the light shielding ring because the amount of light is poor. As long as it is used as a telescope, it is desirable to have at least an F value of 4 or more. Based on this, it can be said that there is no problem because the above calculation can sufficiently maintain the light shielding effect without considering the focal lengths 2, 3, and 4.

However, this calculation does not include the refractive index of glass.
Basically, the shorter the focal length, the thicker the ring, and the longer the focal length, the thinner the ring.

The reason why chromatic aberration cannot be eliminated is that colors with different wavelengths are mixed in visible light, and they have different focal points.

Visible light has an infinite number of wavelengths, or so to speak, colors, but optical filters are used to divide them into the three primary colors of blue, red, and green.

Although it is impossible to eliminate lateral chromatic aberration, it is possible to reduce longitudinal chromatic aberration to almost zero.

represents the configuration, optical path and focus of the multifocal lens 1 and the optical filter 8 . represents the optical path and focal point when the light shielding ring 12 is used and not used, and represents the thickness of the light shielding ring 11 .

By combining an optical filter that can extract only specific light wavelengths and a multifocal lens,
A telescope that achieves achromaticity without using multiple lenses.

Claims (1)

A lens that uses multiple filters that only pass light of specific wavelengths and passes them through a multifocal lens to focus and eliminate chromatic aberration.

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