Compact folded lenses with large apertures

1. A folded lens assembly comprising: from an object side to an image side,

a) a positive first lens element L 1 with a first optical axis and a first lens width W 1 ;

b) a light folding element;

c) a negative second lens element L 2 and a plurality of additional lens elements L 3 -L N with a common second optical axis; and

d) an image sensor having a sensor diagonal length (SDL),

wherein the light folding element is configured to fold light from the first optical axis to the second optical axis, wherein the folded lens has an optical height OH, wherein SDL/OH>0.7 and wherein OH/W 1 <1.1.

2. The folded lens assembly of claim 1 , wherein SDL/OH>1.

3. The folded lens assembly of claim 1 , wherein OH/W 1 <0.95.

4. The folded lens assembly of claim 1 , wherein the lens assembly has a back focal length (BFL) and a total track length (TTL) and wherein BFL/TTL>0.2.

5. The folded lens assembly of claim 1 , wherein the lens assembly has a back focal length (BFL) and a total track length (TTL) and wherein BFL/TTL>0.35.

6. The folded lens assembly of claim 1 , wherein the first lens element has a length A 1 and wherein OH/A 1 <1.4.

7. The folded lens assembly of claim 1 , wherein the first lens element has a length A 1 and wherein OH/A 1 <1.1.

8. The folded lens assembly of claim 1 , wherein the lens assembly includes at least two air gaps between lens elements that comply with the condition STD<0.020, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

9. The folded lens assembly of claim 1 , wherein the lens assembly includes at least two air gaps between lens elements that comply with the condition STD<0.010, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

10. The folded lens assembly of claim 1 , wherein the lens assembly includes at least three air gaps between lens elements that comply with the condition STD<0.035, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

11. The folded lens assembly of claim 1 , wherein the lens assembly includes at least three air gaps between lens elements that comply with the condition STD<0.015, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

12. The folded lens assembly of claim 1 , wherein the lens assembly includes at least four air gaps between lens elements that comply with the condition STD<0.050, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

13. The folded lens assembly of claim 1 , wherein the lens assembly includes at least four air gaps between lens elements that comply with the condition STD<0.025, where STD is a normalized gap standard deviation and r norm is a minimum value of half a gap between adjacent surfaces L i S 2 and L i+1 S 1 .

14. The folded lens assembly of claim 1 , wherein the lens assembly includes, from the object side to the image side five lens elements with any one of the following power sign sequence: PNPPN, PNNPN, PNNNP, PNPNN, and PNPNP.

15. The folded lens assembly of claim 1 , wherein the lens assembly includes at least one air gap between lens elements that complies with the conditions STD<0.01 and OA_Gap/TTL<1/80, where STD is a normalized gap standard deviation and OA_Gap is an on-axis gap.

16. The folded lens assembly of claim 1 , wherein the lens assembly includes at least one air gap between lens elements that complies with the conditions STD<0.01 and OA_Gap/TTL<1/65, where STD is a normalized gap standard deviation and OA_Gap is an on-axis gap.

17. The folded lens assembly of claim 1 , wherein the first and second lens elements and a third lens element have respective Abbe numbers larger than 50, smaller than 30 and larger than 50.

18. The folded lens assembly of claim 1 , wherein the second lens element and a third lens element have together a negative effective focal length.

19. The folded lens assembly of claim 1 , wherein the lens assembly has an effective focal length EFL, wherein the first lens element has a focal length f 1 and wherein f 1 /EFL<0.7.

20. The folded lens assembly of claim 1 , wherein the lens assembly has an effective focal length EFL, wherein the first lens element has a focal length f 1 and wherein f 1 /EFL<0.6.

21. The folded lens assembly of claim 1 , wherein the first lens element has a focal length f 1 , wherein the second lens element has a focal length f 2 and wherein |f 2 /f 1 |<1.

22. The folded lens assembly of claim 1 , wherein the first lens element has a focal length f 1 , wherein the second lens element has a focal length f 2 and wherein |f 2 /f 1 |<0.7.

23. The folded lens assembly of claim 1 , wherein L 2 to L N have circular apertures.

24. The folded lens assembly of claim 1 , wherein the lens assembly has an effective focal length (EFL) and a total track length (TTL) and wherein TTL/EFL<1.1.

25. The folded lens assembly of claim 1 , wherein the apertures of the first lens element is cut along the second optical axis.

26. The folded lens assembly of claim 1 , wherein the lens assembly has an effective focal length EFL and a total lens element length (TLL), wherein the TLL/EFL<1.

27. The folded lens assembly of claim 1 , wherein the first lens element is made of glass and wherein the second lens element and the plurality of lens elements are made of plastic.

28. The folded lens assembly of claim 1 , wherein the all the lens elements are made of plastic.