JPS6046409B2 - fisheye lens - Google Patents

Description

[Detailed Description of the Invention] Despite the large diameter ratio of 1:2.8, the lens of the present invention has only 9 lenses (one of which is a built-in filter), making it compact and capable of high-contrast imaging. The present invention relates to a fisheye lens for a 35mm single-lens reflex camera with high performance.

A fisheye lens is a special lens that projects a hemispherical surface onto a flat surface, and in order to form an image while converting an incident ray bundle with a solid angle of 2π into a conical chief ray bundle, the front, -1 mm, 1
1, 1-■, , 1--, ゛/rNf■'--I--・Y♂1Tp'',-l-J-→Pt, has the same configuration as the mouth focus type wide-angle lens Therefore, from a lens design perspective, it can be considered a retrofocus type ultra-wide-angle lens with large negative distortion.

This leading negative lens is convenient for elongating the back focus and flattening the image plane, just like a retrofocus wide-angle lens.

However, a fisheye lens has a special feature in that unlike a retrofocus wide-angle lens, it is not necessary to correct negative distortion generated by this negative lens, but on the contrary, it must be further generated.

This specificity defines the lens configuration of the fisheye lens, but from the perspective of aberration correction, it is an advantageous condition for correcting coma aberration, field curvature, etc. On the other hand, the strong negative lens at the front causes the light beam to diverge strongly, making it difficult to correct spherical aberration and making it difficult to increase the aperture. Further, since the half angle of view is extremely large at 900°, there is a strong tendency for correction of axial aberrations and correction of all off-axis aberrations to be mutually exclusive, and it is especially difficult to correct off-axis chromatic aberrations.

This chromatic aberration is an aberration that is desirable to eliminate because it reduces the contrast of the image.

In order to solve the above-mentioned problems with conventional fisheye lenses, attempts have been made to reduce the aperture ratio or increase the number of lens elements.

By adopting the following configuration and conditions, the fisheye lens of the present invention has compact and high-contrast imaging performance despite its large aperture ratio, and can solve this problem with a small number of lenses. This is the solution.

That is, a strong negative meniscus lens is arranged as the first lens, a positive meniscus lens made of glass with large dispersion is arranged as the second lens to increase the ability to correct lateral chromatic aberration, a negative lens is used as the third lens, and a negative meniscus lens is used as the fourth lens. A positive lens and a fifth lens filter are installed in the front, and the sixth lens is a thick positive lens to facilitate correction of coma and astigmatism, and the seventh lens after the aperture has a concave surface facing the object. Positive meniscus lens, the 8th lens is a biconvex cemented lens with the cemented surface facing the object concavely, and the 7th and 8th positive lenses have the function of increasing negative distortion and correcting spherical aberration. I am doing it.

In particular, by providing a cemented surface only on the rearmost lens and giving the cemented surface a diverging effect, chromatic aberration is effectively corrected.

The fisheye lens of the present invention has such a configuration, but f: focal length of the entire system Fi: focal length of each single lens counted in order from the top 2 (1
=1...9) R,,D,,N,: Curve radius, surface spacing, refractive index counted in order from the beginning (1=1.2...
Condition (1) is necessary to eliminate astigmatism and increase negative distortion.

When it is smaller than the lower eye, the effect of 3 is not sufficient, and when it exceeds the upper limit, the system becomes large and the correction of astigmatism becomes excessive, which is not preferable. Condition (2) defines the cemented surface of the rearmost lens, but by setting Rl6 to O, the angle of incidence of the three axial light beams to this surface is increased, and the angle of incidence of the three axial light beams on this surface is increased. The angle of incidence of the light ray is increased and the angle of incidence of the upper ray is decreased, thereby making it possible to satisfactorily correct chromatic aberrations such as spherical aberration and coma aberration.

When the upper limit is exceeded, the correction is excessive, and when the lower limit is exceeded by 4, the correction is insufficient. Condition (3) gives the power relationship of the positive lens placed before the aperture. When F2 exceeds the upper limit, the lateral chromatic aberration cannot be sufficiently corrected, and when it exceeds the lower limit, the distortion is in the positive direction. This is not desirable because it moves.

If F4 exceeds this range, coma aberration cannot be corrected well over the entire angle of view, and if F6 is smaller than F2, coma aberration worsens, which is not preferable. Next, examples will be shown.

However, R,, Di,, n,, ν, indicates the radius of curvature, lens surface spacing, refractive index, and Atsube number counted in order from the beginning.

Brief explanation of the threshold plane. Figure 1 is a cross-sectional view of this example, Figure 2 A and b are spherical aberrations,
Astigmatism, c indicates a deviation from the equisolid angle projection y=2fsin;

Claims (1)

[Claims] 1. The first lens is a negative meniscus lens with a convex surface facing the object, the second lens is a positive meniscus lens made of glass with large dispersion and has a convex surface facing the object, the third lens is a negative lens, and the fourth lens is a negative meniscus lens with a convex surface facing the object. The lens is a positive lens, the 5th lens is a built-in filter, the 6th lens is a positive lens with a large center thickness, the 7th lens is a positive meniscus lens with a concave surface facing the object,
The 8th lens group has a cemented positive lens structure, (1) 0
．． 8f<d_7+d_1_1<1.1f(2)0.3/
f<|(n_9-n_8)/r_1_6|<0.5/f
, r_1_6<0(3)2f<3f_4<f_2<f_
A fisheye lens characterized by 6 conditions. However, f: Focal length of the entire system f_i: Focal length of each single lens counted from the beginning (i
=1...9) r_i, d_i, n_i: Curve radius, surface spacing, refractive index (i = 1.2・
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