Ocular optical system

1. An ocular optical system, applied to imaging rays from a display screen into an observer's eye via said ocular optical system, with an eye side facing toward said observer's eye 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 a display-side surface facing toward said display side, wherein:

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

said third lens element has negative refractive power; and

said fourth lens element has a display-side surface with a concave portion in a vicinity of said optical-axis and lens elements having refractive power of the ocular optical system consist only of the four lens elements described above.

2. The ocular optical system of claim 1 , wherein ALT is a total thickness of all four lens elements and ER is a distance between a pupil of said observer and said first lens element to satisfy ALT/ER≤3.4.

3. The ocular optical system of claim 1 , wherein G 12 is an air gap between said first lens element and said second lens element along said optical axis, G 23 is an air gap between said second lens element and said third lens element along said optical axis and G 34 is an air gap between said third lens element and said fourth lens element along said optical axis to satisfy G 34 /(G 12 +G 23 )≤10.9.

4. The ocular optical system of claim 1 , wherein AAG is a sum of all three air gaps between each lens elements from said first lens element to said fourth lens element along said optical axis, G 12 is an air gap between said first lens element and said second lens element along said optical axis and G 23 is an air gap between said second lens element and said third lens element along said optical axis to satisfy AAG/(G 12 +G 23 )≤11.9.

5. The ocular optical system of claim 1 , wherein TTL is a distance between an eye-side surface of said first lens element and said display screen and ER is a distance between a pupil of said observer and said first lens element to satisfy TTL/ER≤4.4.

6. The ocular optical system of claim 1 , wherein T 1 is a thickness of said first lens element along said optical axis and T 4 is a thickness of said fourth lens element along said optical axis to satisfy T 4 /T 1 ≤1.6.

7. The ocular optical system of claim 1 , wherein SL is a distance between a pupil of said observer and said display screen and ER is a distance between a pupil of said observer to an eye-side surface of said first lens element to satisfy SL/ER≤5.4.

8. The ocular optical system of claim 1 , wherein EFL is an effective focal length of said ocular optical system to satisfy 3≤250 mm/EFL≤15.

9. An ocular optical system, applied to imaging rays from a display screen into an observer's eye via said ocular optical system, with an eye side facing toward said observer's eye 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 a display-side surface facing toward said display side, wherein:

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

said second lens element has positive refractive power, a display-side surface with a concave portion in a vicinity of said optical axis and an eye-side surface with a concave portion in a vicinity of its periphery; and

said fourth lens element has a display-side surface with a concave portion in a vicinity of said optical-axis and lens elements having refractive power of the ocular optical system consist only of the four lens elements described above.

10. The ocular optical system of claim 9 , wherein T 4 is a thickness of said fourth lens element along said optical axis, G 12 is an air gap between said first lens element and said second lens element along said optical axis and G 23 is an air gap between said second lens element and said third lens element along said optical axis to satisfy T 4 /(G 12 +G 23 )≤6.4.

11. The ocular optical system of claim 9 , wherein ALT is a total thickness of all four lens elements and T 1 is a thickness of said first lens element along said optical axis to satisfy ALT/T 1 ≤5.

12. The ocular optical system of claim 9 , wherein AAG is a sum of all three air gaps between each lens elements from said first lens element to said fourth lens element along said optical axis and T 1 is a thickness of said first lens element along said optical axis to satisfy AAG/T 1 ≤3.7.

13. The ocular optical system of claim 9 , wherein EFL is an effective focal length of said ocular optical system and ER is a distance between a pupil of said observer to an eye-side surface of said first lens element to satisfy EFL/ER≤4.1.

14. The ocular optical system of claim 9 , wherein T 3 is a thickness of said third lens element along said optical axis, G 12 is an air gap between said first lens element and said second lens element along said optical axis and G 23 is an air gap between said second lens element and said third lens element along said optical axis to satisfy T 3 /(G 12 +G 23 )≤16.5.

15. An ocular optical system, applied to imaging rays from a display screen into an observer's eye via said ocular optical system, with an eye side facing toward said observer's eye 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 a display-side surface facing toward said display side, wherein:

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

said third lens element has a display-side surface with a concave portion in a vicinity of said optical-axis; and

said fourth lens element has a display-side surface with a concave portion in a vicinity of said optical-axis and lens elements having refractive power of the ocular optical system consist only of the four lens elements described above.

16. The ocular optical system of claim 15 , wherein SL is a distance between a pupil of said observer and said display screen, G 12 is an air gap between said first lens element and said second lens element along said optical axis and G 23 is an air gap between said second lens element and said third lens element along said optical axis to satisfy SL/(G 12 +G 23 )≤30.7.

17. The ocular optical system of claim 15 , wherein T 1 is a thickness of said first lens element along said optical axis, T 3 is a thickness of said third lens element along said optical axis, G 23 is an air gap between said second lens element and said third lens element along said optical axis and G 4 D is a distance between said fourth lens element and said display screen along said optical axis to satisfy (T 1 +G 4 D)/(G 23 +T 3 )≤3.6.

18. The ocular optical system of claim 15 , wherein T 1 is a thickness of said first lens element along said optical axis and T 2 is a thickness of said second lens element along said optical axis to satisfy T 1 /T 2 ≤1.3.

19. The ocular optical system of claim 15 , wherein T 1 is a thickness of said first lens element along said optical axis and T 3 is a thickness of said third lens element along said optical axis to satisfy T 1 /T 3 ≤1.6.

20. The ocular optical system of claim 15 , wherein TTL is a distance between an eye-side surface of said first lens element and said display screen and T 1 is a thickness of said first lens element along said optical axis to satisfy TTL/T 1 ≤10.7.