JPH02293710A - Rear attachment lens for telephoto lens - Google Patents

Abstract

PURPOSE:To extend the back focus of a master lens and to correct the deterioration in image performance by disposing, successively from a master lens side, a combined lens having a positive refracting power as a whole, a biconcave lens and a positive meniscus lens and satisfying specific specifications. CONSTITUTION:The rear attachment lens which is mounted between the master lens and a camera and extends the focal distance of the master lens is constituted by disposing, successively from the master lens side, the negative meniscus lens, the concave face of which is directed to the image side, the combined lens which consists of the biconvex lens and has the positive refracting power as a whole and the positive meniscus lens, the convex face of which is directed to the master lens side. Further, the rear attachment lens is provided with the specifications satisfying equation where the radii of curvature of the respective lens faces are designated as ri, the axial spacings between the lens faces as di and the proportional magnification for the focal distance f of the attachment as alpha. The rear attachment lens of about 1.2 times magnification which corrects the deterioration in the image performance by the extended focal distance and simultaneously and nearly maintains the F-number of the master lens is thereby obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rear ψ attachment lens that is attached between a master lens and a camera body to expand the focal length of the master lens, and is particularly suitable for telephoto lenses. This invention relates to a rear attachment lens for back focus extension with a magnification of approximately 1.2 times.

[Conventional technology]

Conventionally, the objective was to attach it between the master lens and the camera to extend the back focus of the master lens, correct the deterioration in image performance due to the expansion of the focal length, and at the same time maintain almost the F number of the master lens. There are rear attachment lenses, but most of these are designed with the pupil position of the master lens relatively close to the rear attachment lens, and the master lens is a wide-angle to standard photographic lens.

Therefore, if these rear attachment lenses are attached to a general telephoto master lens whose pupil position is relatively far from the rear attachment lens, the pupil position will be significantly different, resulting in poor image performance. Another drawback is that the amount of peripheral light is significantly reduced. In order to obtain sufficient peripheral illumination with these rear attachment lenses,
This is not a good idea as it requires increasing the diameter of the rear attachment lens or increasing the magnification, sacrificing image performance and F-number.

On the other hand, there is a rear attachment lens that is designed specifically for telephoto lenses and whose main purpose is to expand the focal length, but it has a magnification of 1.2.
In most cases, it is about 2x to 2x, and in particular, since the rear attachment lens itself has negative refractive power, it is affected by a large negative Pechhar's sum, and the image performance tends to deteriorate significantly.

The present invention mainly aims to extend the hack focus of the master lens, correct the deterioration of image performance due to the enlargement of the focal length, and at the same time almost maintain the F number of the master lens. The purpose of the present invention is to provide a rear attachment lens for a telephoto lens that secures high image performance and sufficient amount of peripheral light.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1(A) is a sectional view of the master lens, and FIG. 2(B) is a sectional view of the attachment lens.

The rear attachment lens according to the present invention includes, in order from the master lens side, a cemented lens with positive refractive power as a whole consisting of a negative meniscus lens with a concave surface facing the image side, a biconvex lens, a biconcave lens, and a double convex lens with the convex surface facing the master lens side. Consisting of a positive meniscus lens, r1 is the radius of curvature of each lens surface, d is the distance between lens surfaces on each axis, n1 is the refractive index of each lens with respect to the d-line, νi is each Atsube number, and f is the focal length of the attachment lens. , Do is the distance from the front principal point of the rear attachment lens to the imaging point of the master lens, and α is a proportional multiple of r:, d:, f, then f=-100 D. =43.89R1=88.
922 DI=0.71 N1=1.88
300 νl=40.8R2=19.084
D2=2.67R3=-35.297D
3=1.65R4=-35.550 D4=0
．． 71R5=68.103 D5=0.07R6
=27.743 D6=1.43R7=76
．． 003 ν4=45.8 ν3=40.9 N3=1.80610 N2=1.59270 ν2=35.3N4=1
．． 54814 1.90 < α < 4.83 (1) Conditional expression (1) defines a proportional multiple, and within this numerical range is the range of enlargement ratio β that can be taken by the rear attachment of the present invention. becomes 1.3〉β〉1.1. If the lower limit of conditional expression (1) is exceeded, aberration correction and F
This is advantageous in that there are fewer fluctuations in the number, but it is difficult to secure peripheral light and sufficient back focus.
It's not good because it's getting worse. If the upper limit of conditional expression (1) is exceeded, that is, β>1.3, the negative refractive power of the rear attachment lens becomes strong, which deteriorates the image plane and increases the chromatic aberration of magnification, which is not preferable. Also, the F number becomes large, which is not preferable.

Numerical examples of the present invention are shown below.

In the example, α-2.126, and at this time f=-212
．． 617, D. =43.887, β=1.2
6. Also, the F number drop of the master lens is % steps.

The following conditional expression is satisfied.

Master lens attachment lens RI R2 R3 R4 R5= R6= R7= R82 R9 RIO R11= R12 R13= R14= R15 F=293 FNO 131.134 DI=16.98462.9
30 D 2 = 0.70109.301
D3=16.92459.308 D4=
3.43342.894 D5=5.542
61.967 D 6=29.0146.931
D 7 = 6.104.1.740 D 8
219.15216.775 D 9= 5.1
073.618 D10=2.49 86.037 D11=20.62291.218
DI2=2.4946.016 D13=8
．． 74 204.371 D14=3. OO■ Aperture 1. 29 N1=1.43387 N2 = 1.4.9700 N3=1.72047 N4=1.58913 N5 1.80518 N6=1.61340 N7 == 1.64. OOO N8=1.61800 νI =95.1 ν2=81.6 ν3=34.7 ν4=61.2 ν5=25.4 ν6=43.8 ν7=60.1 ν8=63.4 rl= 189. 064 D1=1.50N
1=1.88300 v 1=40.8r2-
40.575 D2=5.67 N2=1.5
9270 ν2=35.3r3=-75.048
D3=3.50r4=-75,586
D4=1.50 N3=1.80610
v3=40.9r5=144.799D5
=0.15r6=58.987 D6=3.03
N4=1.54814 v4=45.8r
7=161.596 [Effects of the Invention] As explained above, according to the present invention, the back focus of the master lens is mainly extended, and at the same time, the deterioration of image performance due to the enlargement of the focal length is corrected, and at the same time, the F of the master lens is Magnification of 1.2 with the aim of almost maintaining the number.
It is possible to provide a rear attachment lens for extending the focal length, which is suitable for a telephoto lens, which is a rear attachment lens around the magnification of magnification, and which secures high image performance and sufficient amount of peripheral light.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to an embodiment of the present invention, and FIG. 2 is an aberration diagram of the embodiment. In FIG. 2, d is the d line, g is the g line, and S. C indicates a sine condition, ΔS indicates a sagittal image plane, and ΔM indicates a meridional image plane. 1 song (%) Good N24X 3 pieces

Claims (1)

[Claims] In a rear attachment lens that is attached between a master lens and a camera to expand the focal length of the master lens, the attachment lens has a negative meniscus with a concave surface facing the image side in order from the master lens side. The overall structure consists of a cemented lens with a positive refractive power, a biconcave lens, and a positive meniscus lens with a convex surface facing the master lens. r_i is the radius of curvature of each lens surface, and d_i is the lens surface on each axis. The interval, n_i is the refractive index of each lens with respect to the d-line, ν_i is each Atsube number, f is the focal length of the attachment lens, D_o is the distance from the front principal point of the rear attachment lens to the imaging point of the master lens, and α is A rear attachment lens for a telephoto lens that satisfies the following specifications: ▲Mathematical formulas, chemical formulas, tables, etc.▼1.90<α<4.83 when expressed as a proportional multiple to r_i, d_i, f.