JPH01307713A - Enlarging projection lens - Google Patents

Abstract

PURPOSE:To obtain high >=X20 power image forming performance up to the periphery by constituting a 2nd lens group by cementing a 1st positive lens which has a larger-curvature surface on its incidence side, a 2nd biconcave lens, and a 3rd biconvex lens and satisfying specific conditions. CONSTITUTION:The 2nd lens group is constituted by cementing the 1st positive lens which has the larger-curvature surface on its incidence side, the 2nd biconcave lens, and the 3rd biconvex lens and inequalities I-V hold. In the inequalities I-V, (f) is the focal length of the whole system, f1 the focal length of an (i)th lens group, r1 the radius of curvature of an (i)th surface from the incidence side, n+ the mean refractive index of the positive lenses of the 2nd and 3rd lens groups, nu1 the Abbe number of the (i)th lens, nu+ the mean Abbe number of the positive lenses of the 2nd and 3rd lens groups, and nu- the mean Abbe number of the negative lenses of the 2nd and 3rd lens groups. Consequently, the lens which has about x-20 high power and its distortion, power chromatic aberration, astigmatism, and curvature of field compensated excellent is obtained.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an enlarged projection lens that is applied to enlarge and project an image formed by, for example, an objective lens of an astronomical telescope. [Prior Art] Generally, an eyepiece lens is simply used as a lens for enlarging and projecting an image formed by an objective lens or the like of an astronomical telescope. However, the eyepiece lens has aberrations corrected in the afocal state for visual viewing, and when used for enlarged projection, distortion, curvature of field, lateral chromatic aberration, etc. occur due to changes in the magnification used. There was a problem in that excessive aberrations occurred. [Object of the invention] This invention provides an F number of 1:6. It is an object of the present invention to provide an enlarged projection lens that includes a half angle of view of about 1 B' in combination with an objective lens of about 0.0 and has high imaging performance up to the periphery at a magnification of -20 times or more. [Means for Solving the Problems] In order to achieve the above object, the magnifying projection lens of the present invention includes, in order from the incident side, a 1121st group which is a positive meniscus lens with a convex surface facing the projection surface, and a positive second lens. The third lens group is a positive meniscus lens with its convex surface facing the incident side, and the second lens group consists of a positive first lens with its surface with greater curvature facing the incident side, and a biconcave lens group. Consisting of two lenses and a biconvex third lens, ■ n, > 1.70 ■ yl>45.0 ■ v * -y -> 16.0 ■ f+/f>4.0 ■ 1 .3<-r+/f<1.7 However, f: Focal length of the entire system fI = Focal length of the i-th lens group rI = Radius of curvature n of the first surface from the incident side,: Second.
Average refractive index of the positive lens of the third lens group V1: Atsube number V of the i-th lens: 2nd. Average y- of the positive lens numbers of the third lens group: 2nd. It is characterized in that it is set to satisfy each condition of the average Atsube number of the negative lenses of the third lens group. Condition ■ is the second condition. By keeping the refractive index of the positive lens in the third lens group large, the Petzval sum can be kept small and the field curvature can be reduced below the lower limit of the 0 condition (2), which is a condition for flattening the field. Increase excessively. Conditions (2) and (2) are conditions for correcting chromatic aberration. Condition (2) is a condition for keeping the chromatic aberration of magnification small by keeping the Abbe number of the 1121st lens group, which has positive power, large; below the lower limit, the chromatic aberration of magnification becomes excessive. Also, condition (■) is the second condition. This is a condition for keeping chromatic aberrations small by keeping a large difference between the average Atsube number of the positive lens in the third lens group and the average Atsube number of the negative lens.
Below the lower limit, chromatic aberration becomes excessive. Conditions (1) and (2) relate to the 1121st group having weak power, which is a feature of the present invention. The function of the 1121st lens group is to correct distortion and field curvature without producing lateral chromatic aberration by correcting the direction and focusing position of the light beam focused by the objective lens with weak power. Condition ■ gives the power of the 1121st group. Below the lower limit, the power becomes excessive and lateral chromatic aberration occurs excessively. The third lens group will no longer be able to compensate. Condition (2) is a condition for correcting the distortion aberration occurring in the third lens group in advance and suppressing the occurrence of other aberrations by appropriately setting the radius of curvature of the first surface of the first lens. If the upper limit of condition (■) is exceeded, distortion aberration will be undercorrected, and if it is below the lower limit, coma and other higher-order aberrations will occur excessively, and the radius of curvature will become too small, increasing the cost of polishing. Become. [Example] Hereinafter, an example of the magnifying projection lens according to the present invention will be described. FIG. 1 shows the arrangement of the magnifying projection lens according to the first embodiment of the present invention, and the specific numerical structure is as shown in the table on page 8. The symbol Fno in the table is the F number of the objective lens used in combination with the above magnifying projection lens, f is the focal length of the entire magnifying projection lens system, r is the radius of curvature of each lens surface, and d is the distance between the surfaces III ( lens thickness and air spacing), n-d line (5
The refractive index at 88 nm), y- represents the number. As for the second to sixth embodiments, the lens configurations are almost the same as those shown in FIG. 1, so they are omitted, and only the numerical configurations are shown in Table 6 on page 8.9. The relationship between each embodiment and conditional expressions (1) to (2) is as shown in the table on the next page. (Margin below)

[Example - Conditional expression correspondence table]

The aberration characteristics of these magnifying projection lenses are as shown in FIGS. 2 to 7. Both objective lenses have F number 1
: 6.0, focal length @3.8rrtn, magnification -27
In Figure 6, which shows the state when the magnification and half angle of view is 18', the spherical aberration SA is shown as a solid line, the sine condition SC is shown as a broken line, and the axial chromatic aberration and lateral chromatic aberration are
(588nm), g-Line (436nm), C-L
Three data of ine (656 nm) are shown. For astigmatism, the sagittal direction S is a solid line, and the meridional direction H is a solid line.
is shown with a broken line. In any of the examples, good performance can be obtained by satisfying the conditions (1) to (4). (Hereinafter referred to as "Kinpaku") 1st embodiment 2nd embodiment 3rd embodiment 4th embodiment 5th embodiment 6th embodiment [Effects] As explained above, according to this invention, -1+
This is a magnifying projection lens that can be used in combination with an objective lens with a large aperture of about 6.0, and can effectively correct distortion, chromatic aberration of magnification, astigmatism, and curvature of the field at a high magnification of $ -20x 1 degree. We can provide lenses here. Furthermore, this lens can also be used as an eyepiece.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first example of a magnifying projection lens according to the present invention, and FIGS. 2 to 7 are aberration diagrams of the magnifying projection lenses according to the first to first embodiments of the present invention.

Claims (1)

[Claims] In order from the incident side, the first lens group is a positive meniscus lens with a convex surface facing the projection surface, the second positive lens group, and the third lens group is a positive meniscus lens with a convex surface facing the incident side. It is composed of a lens group, and the second lens group is constructed by laminating together a positive first lens with its surface with a larger curvature facing the incident side, a biconcave second lens, and a biconvex third lens. , (1) n_+>1.70 (2) ν_i>45.0 (3) ν_+-ν_->16.0 (4) f_1/f>4.0 (5) 1.3<-r_i/f< 1.7 However, f: focal length of the entire system f_i: focal length of the i-th lens group r_i: radius of curvature of the i-th surface from the incident side n_+: refractive index of the positive lens of the second and third lens groups Average ν_i: Atsube number of the i-th lens ν_+: Average Atsube number of the positive lenses in the second and third lens groups ν_-: Satisfy each condition of the average Atsube number of the negative lenses in the second and third lens groups A magnifying projection lens featuring