Ocular optical system

1. An ocular optical system, applied to imaging rays from a display screen into a pupil of an observer via said ocular optical system, with an eye side facing toward said pupil of the observer and with a display side facing toward said display screen said ocular optical system from said eye side toward said display side in order along an optical axis comprising: a first lens element, a second lens element, a third lens element and a fourth lens element, said first lens element to said fourth lens element each having an eye-side surface facing toward said eye side and allowing the imaging light to pass through, and as well as a display-side surface facing toward said display side and allowing the imaging light to pass through, wherein:

said first lens element has a display-side surface with a convex portion in a vicinity of its periphery;

said third lens element has an eye-side surface with a convex portion in a vicinity of its periphery;

the ocular optical system does not include any lens element with refractive power other than said first lens element, said second lens element, said third lens element and said fourth lens element, υ1 is an Abbe number of the first lens element, υ4 is an Abbe number of the fourth lens element, SL is a distance between said pupil of said observer and the display screen, T2 is a thickness of said second lens element along the optical axis, ALT is a total thickness of all four lens elements, G34 is an air gap between said third lens element and said fourth lens element along said optical axis, and the ocular optical system satisfies the relationships: 20.00≤|υ1−υ4|, SL/T2≤21.60 and ALT/G34≤8.10.

2. The ocular optical system of claim 1 , wherein ER is a distance between said pupil of said observer and an eye-side surface of said first lens element, and the ocular optical system satisfies the relationship SL/ER≤5.20.

3. The ocular optical system of claim 1 , wherein TTL is a distance between an eye-side surface of said first lens element and the display screen, ER is a distance between said pupil of said observer to an eye-side surface of said first lens element, and the ocular optical system satisfies the relationship TTL/ER≤4.60.

4. The ocular optical system of claim 1 , wherein ER is a distance between said pupil of said observer and an eye-side surface of said first lens element, T4 is a thickness of said fourth lens element along the optical axis, and the ocular optical system satisfies the relationship ER/T4≤6.50.

5. The ocular optical system of claim 1 , wherein G4D is a distance between a display-side surface of said fourth lens element and the display screen along the optical axis, and the ocular optical system satisfies the relationship G4D/T2≤5.60.

6. The ocular optical system of claim 1 , wherein G12 is an air gap between said first lens element and said second lens element along said optical axis, and the ocular optical system satisfies the relationship ALT/(G12+G34)≤2.60.

7. The ocular optical system of claim 1 , wherein EFL is an effective focal length of said ocular optical system, T1 is a thickness of said first lens element along the optical axis, and the ocular optical system satisfies the relationship EFL/T1≤5.70.

8. The ocular optical system of claim 1 , wherein TTL is a distance between an eye-side surface of said first lens element and the display screen, T1 is a thickness of said first lens element along the optical axis, and the ocular optical system satisfies the relationship TTL/T1≤6.90.

9. The ocular optical system of claim 1 , wherein TTL is a distance between an eye-side surface of said first lens element and the display screen, and the ocular optical system satisfies the relationship TTL/T2≤13.80.

10. An ocular optical system, applied to imaging rays from a display screen into a pupil of an observer via said ocular optical system, with an eye side facing toward said pupil of the observer and with a display side facing toward said display screen said ocular optical system from said eye side toward said display side in order along an optical axis comprising: a first lens element, a second lens element, a third lens element and a fourth lens element, said first lens element to said fourth lens element each having an eye-side surface facing toward said eye side and allowing the imaging light to pass through, and as well as a display-side surface facing toward said display side and allowing the imaging light to pass through, wherein:

said first lens element has a display-side surface with a convex portion in a vicinity of its periphery;

said third lens element has positive refractive power;

the ocular optical system does not include any lens element with refractive power other than said first lens element, said second lens element, said third lens element and said fourth lens element, υ1 is an Abbe number of the first lens element, υ4 is an Abbe number of the fourth lens element, SL is a distance between said pupil of said observer and the display screen, T2 is a thickness of said second lens element along the optical axis, ALT is a total thickness of all four lens elements, G34 is an air gap between said third lens element and said fourth lens element along said optical axis, and the ocular optical system satisfies the relationships: 20.00≤υ1−υ4|, SL/T2≤21.60 and ALT/G34≤8.10.

11. The ocular optical system of claim 10 , wherein ER is a distance between said pupil of said observer and an eye-side surface of said first lens element, and the ocular optical system satisfies the relationship SL/ER≤5.20.

12. The ocular optical system of claim 10 , wherein TTL is a distance between an eye-side surface of said first lens element and the display screen, ER is a distance between said pupil of said observer to an eye-side surface of said first lens element, and the ocular optical system satisfies the relationship TTL/ER≤4.60.

13. The ocular optical system of claim 10 , wherein G4D is a distance between a display-side surface of said fourth lens element and the display screen along the optical axis, T4 is a thickness of said fourth lens element along the optical axis, and the ocular optical system satisfies the relationship G4D/T4≤7.50.

14. The ocular optical system of claim 10 , wherein ER is a distance between said pupil of said observer and an eye-side surface of said first lens element, G12 is an air gap between said first lens element and said second lens element along said optical axis, and the ocular optical system satisfies the relationship ER/(G12+G34)≤2.80.

15. The ocular optical system of claim 10 , wherein T1 is a thickness of said first lens element along the optical axis, and the ocular optical system satisfies the relationship SL/T1≤7.90.

16. The ocular optical system of claim 10 , wherein TTL is a distance between an eye-side surface of said first lens element and the display screen, T3 is a thickness of said third lens element along the optical axis, and the ocular optical system satisfies the relationship TTL/T3≤7.90.