JPH10268376A - Diaphragm mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change light quantity stepwise or continuously without spoiling image-forming performance by forming the shape of a light shielding part asymmetrically with respect to an optical axis and like a fan with the optical axis as center, and variably forming the angular range of the fan shape. SOLUTION: A fixed diaphragm 2a shields a center area having a fixed radius with the optical axis as center. A variable diaphragm 2b has such structure that eight light shielding plates having the angular range of about 45 with the optical axis as center espectively are superposed. The eight light shielding plates are pulled out or superposed in a circumferential direction like the fan, and the angular range of the light shielding part S is continuously changed. The light quantity is converged to 7/8 in a state where eight light shielding plates are superposed, about 1/2 in a state where four light shielding plates are pulled out, about 1/4, 1/8 and 1/16 in a state where six, seven or eight light shielding plates are respectively pulled out. As the light shielding plates are pulled out, the light shielding part by the diaphragm mechanism is increased and a light passing part is reduced. Thus, the light quantity entering an optical system is continuously changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a diaphragm mechanism used in an optical system having a center shield.

[0002]

2. Description of the Related Art In a conventional optical system having a center shield, there is usually no stop, and in order to change the amount of light, N
A means of inserting a D filter or the like was used.

[0003]

As described above, in the conventional optical system having a center shield, the N
Since the D filter is used, it is necessary to replace the ND filter for each required light amount, and the light amount cannot be changed quickly. When the light quantity is changed in many steps, filters must be prepared by the number of the steps, and the number of components is large, which is a factor of high cost. Further, according to the density of the prepared ND filter, the light amount could be changed only stepwise, that is, the light amount could not be changed continuously.

Therefore, as shown in FIG. 5, a method of changing the amount of light by putting a normal iris diaphragm 9 near the pupil is also conceivable. However, although it is possible to change the amount of light by such a method, as shown in FIG. 6, there is a disadvantage that the MTF becomes very poor when the aperture is stopped down. Therefore, an object of the present invention is to provide a diaphragm mechanism used in an optical system having a center shield, capable of changing the light amount in a stepwise or continuous manner and capable of obtaining good imaging performance.

[0005]

In order to solve the above-mentioned problems, in the diaphragm mechanism according to the present invention, the shape of the light shielding portion is formed so as to be asymmetric with respect to the optical axis. At this time, it is preferable that the shape of the light shielding portion is a sector around the optical axis and the angle range of the sector is variably formed, thereby changing the light amount stepwise or continuously without impairing the imaging performance. Can be done.

[0006]

Embodiments of the present invention will be described below. 1 and 2 show one embodiment of the present invention.
The optical system 1 to which the aperture mechanism 2 is applied is a Newton-type reflection telescope having a concave mirror 1a and a folding mirror 1b, the focal length is f = 500 mm, and the effective F-number is F /
8 An aperture mechanism 2 according to the present embodiment is disposed on the object side of the folding mirror 1b, and the aperture mechanism 2 includes a fixed aperture 2a and a variable aperture 2b. The fixed aperture 2a is
This shields a central region having a constant radius centered on the optical axis z, and is provided because the optical system 1 includes the folding mirror 1b. Further, as shown in FIG. 2, the variable stop 2b has a structure in which eight light shielding plates each having an angle range of about 45 ° about the optical axis z are stacked. However, the last one of the eight light-shielding plates is provided with a small transmission portion T as shown in FIG. These eight light-shielding plates can be drawn out in a circumferential direction like a fan or can be overlapped, so that the angle range of the light-shielding portion S can be continuously changed. The outer diameter of the fixed stop 2a is φ = 35.74 mm, and the outer diameter of the light transmission region of the variable stop 2b is φ = 72 mm. The diameter of the light transmission region provided on the last one of the eight light shielding plates is φ
= 15.625 mm.

The adjustment of the amount of light by the aperture mechanism 2 will be described with reference to FIG. 2. FIG. 2A is a view of the optical system when the variable aperture 2b is removed, viewed from the optical axis z direction. The ring-shaped portion outside 2a is the transmission portion T
Becomes FIGS. 2B to 2F show a state in which the variable diaphragm 2b is mounted. First, in FIG. 2B, the light amount is reduced to about 7/8 in a state in which all eight light shielding plates are stacked. (C) is about 1/2 when the four light-shielding plates are pulled out, (D) is about 1/4 when six light-shielding plates are drawn, and (E) is seven light-shielding. The amount of light is about 1/8 when the board is pulled out,
In (F), the light amount is reduced to about 1/16 in a state where all the eight light shielding plates are pulled out. As the light-shielding plate is pulled out, the light-shielding portion by the aperture mechanism 2 increases, and the transmission portion T
Is reduced, and thus the amount of light entering the optical system 1 can be changed continuously.

FIG. 3 shows a defocus MTF curve when the aperture mechanism 2 of the present embodiment is used. As is clear from the comparison between FIG. 3 and FIG. 6, when the shape of the light-shielding portion S is symmetrical with respect to the optical axis z, the MTF is significantly reduced when the iris diaphragm is stopped down. Due to the asymmetry with respect to the optical axis, the MTF does not decrease so much even when the aperture is stopped down, that is, good imaging performance can be maintained.

FIG. 4 shows another embodiment of the aperture mechanism. The aperture mechanism 2 of this embodiment comprises two light shielding plates 3, 3.
As shown in FIG. 4A, each light shielding plate 3 is rotatably arranged about the optical axis z, and a small radius portion 3a about the optical axis z is formed in a disk shape so as to form a central light shielding region. The large-radius portion 3b outside the small-radius portion is formed in a sector shape slightly larger than a semicircle. Thus, as shown in FIG. 4B, by changing the mutual arrangement angle of the two light shielding plates 3, the light amount can be changed asymmetrically with respect to the optical axis. Obviously, one of the two light shielding plates 3, 3 can be fixed.

[0010]

As described above, according to the present invention, in an optical system having a central shield, the light amount can be changed stepwise or continuously, and a good imaging performance can be maintained. was gotten.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical system to which an aperture mechanism according to the present invention is applied.

FIG. 2 is a diagram of an optical system to which the aperture mechanism according to the present invention is applied, viewed from an optical axis direction.

FIG. 3 is a diagram showing an MTF of an optical system to which the stop mechanism of the present invention is applied.

FIG. 4 is a front view showing another embodiment of the aperture mechanism.

FIG. 5 is a view of an optical system employing an iris diaphragm as a comparative example, viewed from an optical axis direction.

FIG. 6 is a diagram showing an MTF of the optical system of the comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical system 1a ... Concave mirror 1b ... Folding mirror 2, 3 ... Aperture mechanism 2a ... Fixed diaphragm 2b ... Variable diaphragm 3 ... Shielding plate 3a ... Small radius part 3b ... Large radius part S ... Light shielding part T ... Transmission part z ... Light axis

Claims (2)

[Claims] 1. A stop mechanism for partially blocking an optical path of an optical system having a center shield, wherein the shape of a light blocking portion is formed so as to be asymmetric with respect to an optical axis. 2. The diaphragm mechanism according to claim 1, wherein the shape of the light shielding portion is a sector around the optical axis, and the angular range of the sector is variably formed.