JP3757534B2 - Aperture mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diaphragm mechanism used in an optical system having a central shield.
[0002]
[Prior art]
Conventional optical systems having a central shield usually do not have a diaphragm, and in order to change the amount of light, an ND filter or the like is inserted in the optical path.
[0003]
[Problems to be solved by the invention]
As described above, in the conventional optical system having the central shielding, since the ND filter is used to change the light amount, it is necessary to replace the ND filter for each necessary light amount, and the light amount can be changed quickly. could not. In addition, when changing the amount of light in any number of steps, it is necessary to prepare as many filters as the number of parts. Furthermore, the amount of light can be changed only in steps according to the density of the prepared ND filter, that is, the amount of light cannot be changed continuously.
[0004]
Therefore, as shown in FIG. 5, a method of changing the amount of light by inserting a normal iris diaphragm 9 in the vicinity of the pupil can be considered. However, although it is possible to change the amount of light by such a method, as shown in FIG. 6, there is a drawback that the MTF becomes very poor when the aperture is reduced.
Accordingly, an object of the present invention is to provide an aperture mechanism that can be used in an optical system having a central shield and that can change the amount of light stepwise or continuously and that can provide good imaging performance.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the diaphragm mechanism according to the present invention forms a fan shape centered on the optical axis so that the shape of the light shielding portion is asymmetric with respect to the optical axis , and the angle range of the fan shape is variably formed . Thereby, a single aperture can be formed, and the amount of light can be changed stepwise or continuously without impairing the imaging performance.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. 1 and 2 show an embodiment of the present invention. The optical system 1 to which the diaphragm mechanism 2 is applied is a Newton type reflecting telescope having a concave mirror 1a and a folding mirror 1b, and has a focal length of f = 500 mm and an effective F number of F / 8.
An aperture mechanism 2 according to the present embodiment is disposed on the object side of the folding mirror 1b. The aperture mechanism 2 includes a fixed aperture 2a and a variable aperture 2b. The fixed stop 2a is for shielding a central region having a constant radius with the optical axis z as the center, and is provided because the optical system 1 has 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 ° around 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. The eight light shielding plates can be drawn out or overlapped in the circumferential direction like a fan, whereby the angle range of the light shielding portion S can be continuously changed. The outer diameter of the fixed diaphragm 2a is φ = 35.74 mm, and the outer diameter of the light transmission region of the variable diaphragm 2b is φ = 72 mm. Further, the diameter of the light transmission region provided in the last one of the eight light shielding plates is φ = 15.625 mm.
[0007]
The adjustment of the amount of light by the diaphragm mechanism 2 will be described with reference to FIG. 2. FIG. 2A is a view of the optical system when the variable diaphragm 2b is removed as viewed from the direction of the optical axis z. The ring-shaped part is the transmission part T. FIGS. 2B to 2F show a state where the variable diaphragm 2b is mounted. First, FIG. 2B shows a state in which all of the eight light shielding plates are stacked, and the light amount is reduced to about 7/8. (C) is about 1/2 light quantity with 4 light shielding plates pulled out, (D) is about 1/4 light quantity with 6 light shielding plates pulled out, and (E) is 7 light shieldings. The light quantity is reduced to about 1/8 when the plate is pulled out, and (F) is reduced to about 1/16 when all the eight light shielding plates are pulled out. As the light shielding plate is pulled out, the light shielding portion by the diaphragm mechanism 2 increases and the transmission portion T decreases, and thus the amount of light entering the optical system 1 can be continuously changed.
[0008]
FIG. 3 shows a defocus MTF curve when the diaphragm 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 symmetric with respect to the optical axis z, the MTF is significantly reduced when the iris diaphragm is stopped, but in this embodiment, the shape of the light shielding portion S is Due to asymmetry with respect to the optical axis, the MTF does not decrease much even when the aperture is reduced, that is, good imaging performance can be maintained.
[0009]
FIG. 4 shows another embodiment of the diaphragm mechanism, and the diaphragm mechanism 2 of this embodiment is composed of two light shielding plates 3 and 3. Each light shielding plate 3 has an optical axis as shown in FIG. The small radius portion 3a centering on the optical axis z is formed in a disc shape so as to be a central light shielding region, and the large radius portion 3b outside the small radius portion is The fan shape is slightly larger than the semicircle. Thus, as shown in FIG. 4B, the light quantity can be changed asymmetrically with respect to the optical axis by changing the mutual arrangement angle of the two light shielding plates 3 and 3. Obviously, one of the two light shielding plates 3 and 3 can be fixed.
[0010]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain an aperture mechanism that can change the amount of light stepwise or continuously in an optical system having a central shield and can maintain good imaging performance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an optical system to which the diaphragm mechanism of the present invention is applied. FIG. 2 is a diagram of an optical system to which the diaphragm mechanism of the present invention is applied as viewed from the optical axis direction. FIG. 4 is a front view showing another embodiment of the diaphragm mechanism. FIG. 5 is a diagram showing an optical system employing an iris diaphragm as a comparative example as seen from the optical axis direction. 6 is a diagram showing the MTF of the optical system of the above comparative example.
DESCRIPTION OF SYMBOLS 1 ... Optical system 1a ... Concave mirror 1b ... Folding mirror 2, 3 ... Diaphragm mechanism 2a ... Fixed aperture 2b ... Variable aperture 3 ... Light-shielding plate 3a ... Small radius part 3b ... Large radius part S ... Light-shielding part T ... Transmission part z ... Light axis

Claims (1)

An aperture mechanism that partially blocks the optical path of an optical system having a fixed aperture that blocks the central region of the optical axis, and has a fan shape centered on the optical axis so that the shape of the light-shielding portion is asymmetric with respect to the optical axis. A diaphragm mechanism characterized in that the angle range is variably formed to form a single opening .

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