Optical system and eye piece
An eye piece (EL 1 ) is formed having a first lens (L 1 ) having a positive refractive power and a second lens (L 2 ) having a positive refractive power, which are disposed in order from an object (O), and a contact multi-layer diffractive optical element (DOE), which has a first optical element ( 51 ) formed with a relief pattern and a second optical element ( 52 ) which is in contact with the surface of the first optical element ( 51 ) where the relief pattern is formed, is disposed on an optical surface of the first lens (L 1 ) or the second lens (L 2 ).
1. An optical system comprising a first lens and a second lens having a positive refractive power, which are disposed in order from an object, characterized in that
a contact multi-layer diffractive optics, which has a first optical element formed with a relief pattern and a second optical element, which is in contact with the surface of the first optical element where the relief pattern is formed, is disposed on an optical surface of the first lens or the second lens, and characterized in that
the difference of refractive indexes on a d-line between the first optical element and the second optical element is 0.45 or less, and the following expression is satisfied:
0.002 <D/f <2.0
where D is an air distance on an optical axis between the first lens and the second lens, and f is a focal length of the entire optical system.
2. The optical system according to claim 1 , characterized in that the condition of the following expression is satisfied:
0 <D/ ( f 1× f 2)<0.15
where f1 is a focal length of the first lens, f2 is a focal length of the second lens, and f1>0 and f2>0.
3. The optical system according to claim 1 , characterized in that the condition of the following expression is satisfied:
−0.1 <D/ ( f 1× f 2)<0
where f1 is a focal length of the first lens, f2 is a focal length of the second lens, and f1<0, f2>0 and |f1|>|f2|.
4. The optical system according to claim 1 , characterized in that at least one optical surface of the first lens and the second lens is aspherical.
5. The optical system according to claim 1 , characterized in that the contact multi-layer diffractive optics is formed on a surface of the first lens, the face facing the object.
6. The optical system according to claim 1 , characterized in that the first optical element is formed using one of a material having a relatively high refractive index and low dispersion, and a material having a relatively low refractive index and high dispersion, and the second optical element is formed using the other one of the materials, and
the condition of the following expression is satisfied:
50 <Δνd/Δnd< 2000
where Δνd is a difference of Abbe numbers between the first optical element and the second optical element, and Δnd is a difference of refractive indexes on a d-line between the first optical element and the second optical element.
7. The optical system according to claim 1 , characterized in that the condition of the following expression is satisfied:
( Eg+EC )/2>0.9 ×Ed
where Ed is a diffraction efficiency of the contact multi-layer diffractive optics on a d-line, Eg is a diffraction efficiency of the contact multi-layer diffractive optics on a g-line, and EC is a diffraction efficiency of the contact multi-layer diffractive optics on a C-line.
8. The optical system according to claim 1 , characterized in that the condition of the following expression is satisfied:
0.0001 <p/f< 0.003
where p is a minimum pitch of the relief pattern and f is a focal length of the entire optical system.
9. The optical system according to claim 1 , characterized in that the condition of the following expression is satisfied:
0.1<φ× R/f 2 <2.0
where f is a focal length of the entire optical system, φ is a pupil diameter, and R is eye relief.
10. An eye piece for observing an image of an object, the eyepiece having an optical system, and the optical system comprising a first lens and a second lens having a positive refractive power, which are disposed in order from an object, the optical system being characterized in that
a contact multi-layer diffractive optics, which has a first optical element formed with a relief pattern and a second optical element, which is in contact with the surface of the first optical element where the relief pattern is formed, is disposed on an optical surface of the first lens or the second lens, and characterized in that
the difference of refractive indexes on a d-line between the first optical element and the second optical element is 0.45 or less, and the following expression is satisfied:
0.002 <D/f< 2.0
where D is an air distance on an optical axis between the first lens and the second lens, and f is a focal length of the entire optical system.