Multi-focus system for a low light level vision apparatus

• US 5,175,651 A
• Filed: 03/01/1991
• Issued: 12/29/1992
• Est. Priority Date: 03/17/1989
• Status: Expired due to Fees

• Current Assignee: Environmental Research Institute Incorporated
• Original Assignee: Environmental Research Institute of Michigan
• Inventors: Marron, Joseph C., Tai, Anthony M.
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US07/663,270
• Time in Patent Office: 669 Days
• Field of Search: 359/721, 359/722, 359/723, 359/494, 359/498, 359/566, 359/570, 250/213 VT
• US Class Current: 359/721
• CPC Class Codes: G02C 7/041 bifocal; multifocal
• CPC Class Codes: G02C 7/06 bifocal; multifocal ; progressive G02C7/041 takes precedence

Abstract

A night vision apparatus 10 includes a first focusing refracting lens 28 which focuses light rays 29 from distant scene 14 onto a light intensifier 30. The kinoform 40 or bifringent lens 78 are disposed in the light path to allow light rays 35 from near scene 18, 20, 22 and 24 to be focused onto light intensifier 30 to form a multi-focus night vision apparatus with increased depth of focus.

Claims

1. An apparatus for low light optical use including a light intensifier of forming an intensified image of a light image received thereon, the improvement characterized by:

first and second focusing means disposed in tandem in a light path from respective first and second distance for focusing light from the respective first and second distances onto the light intensifier;

said second focusing means being coextensive with an objective aperture defined by said first focusing means and having essentially the same wavelength band pass characteristic as said first focusing means.

2. An apparatus as defined in claim 1 further characterized by:

said first focusing means includes a diffraction lens positioned in and substantially filling said objective aperture, said second focusing means transmitting throughout said objective aperture a first portion of light diffracted thereby and a second portion of light undiffracted thereby, whereby

said first portion of light from said second distance diffracted by said diffraction lens is focused in conjunction with said refracting lens onto the light intensifier, and

said second portion of light from said first distance undiffracted by said diffraction lens is focused solely by said refracting lens onto the light intensifier.

3. An apparatus as defined in claim 2 further characterized by:

said diffraction lens being a separate member and mountable adjacent said refracting lens.

4. An apparatus as defined in claim 3 further characterized by:

said refracting lens being interposed between said diffraction lens and the light intensifier such that said diffracted light is diffracted first before being refracted by said refracting lens onto the light intensifier.

5. An apparatus as defined in claim 2 further characterized by:

said diffraction lens and said refracting lens being integrally formed.

6. An apparatus as defined in claim 2 further characterized by:

a single adjustable iris disposed in the light path from said respective first and second distances and in proximity to said objective aperture for adjusting the amount of light impinging on the light intensifier from said first and second distances.

7. An apparatus as defined in claim 1 further characterized by:

said first focusing means includes a refracting birefringent lens wherein light of a first polarity from the first distance is focused onto said light intensifier; and

said second focusing means includes said refracting birefringent lens wherein light from said second distance having a second polarity substantially orthogonal to the first polarity is focused onto said light intensifier.

8. An apparatus as defined in claim 7 further characterized by:

a polarizing filter being disposed in the light path to the light intensifier and being adjustable with respect to said birefringent lens to vary the ratio of light of said first polarity and said second polarity being transmitted therethrough.

9. An apparatus as defined in claim 1 further characterized by:

said first focusing means includes a refracting lens constructed with a focal length such that light from the first distance is focused onto said light intensifier;

said second focusing means includes a birefringent lens constructed such that light of a first polarity passes through said birefringent lens with no focusing effect such that said light of said first polarity from said first distance is focused onto the light intensifier solely by said refracting lens and light from said second distance having a second polarity substantially orthogonal to said first polarity is focused by said birefringent lens in conjunction with the refracting lens onto said light intensifier.

10. An apparatus as defined in claim 9 further characterized by:

a polarizing filter in the light path to the light intensifier and adjustable with respect to said birefringent lens to vary the ratio of light of said first polarity and light of said second polarity being transmitted therethrough.

11. A multi-focus low light vision apparatus comprising:

a light intensifier having an input screen and an output screen for producing at said output screen a light intensified image of a light image impinging on said input screen;

a first focusing means having an objective aperture and essentially no spectral filtering; and

a second focusing means having said objective aperture and essentially no spectral filtering, said first and second focusing means disposed in tandem whereby a portion of light from a first distance passes through both said first and second focusing means and is focused thereby onto said input screen of said light intensifier and a portion of light from a second distance passes through both said first and second focusing means and is focused thereby onto said input screen of said light intensifier.

12. The multi-focus low light vision apparatus as claimed in claim 11, whereby:

said first focusing means includes a refracting lens having a focal length for focusing light from the first distance onto said input screen of said light intensifier; and

said second focusing means includes a diffraction lens transmitting throughout said objective aperture a first diffracted portion of light and a second undiffracted portion of light, said first diffracted portion of light from said second distance diffracted by said diffraction lens in an amount for said refracting lens to focus said first diffracted portion of light from said second distance onto said input screen of said light intensifier, and said second undiffracted portion of light from said first distance being focused solely by said refracting lens onto said input screen of said light intensifier.

13. The multi-focus low light vision apparatus as claimed in claim 12, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth selected with regard to a predetermined wavelength for providing a predetermined proportion of said first diffracted portion of light and said second undiffracted portion of light.

14. The multi-focus low light vision apparatus as claimed in claim 13, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth of one half said predetermined wavelength for providing approximately equal proportions of received light in said first diffracted portion of light and said second undiffracted portion of light.

15. The multi-focus low light vision apparatus as claimed in claim 13, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth of one fifth said predetermined wavelength for providing approximately 20% of received light in said second undiffracted portion of light.

16. The multi-focus low light vision apparatus as claimed in claim 11, whereby:

said first focusing means includes a refracting lens having a focal length for focusing light from the first distance onto said input screen of said light intensifier; and

said second focusing means includes a kinoform lens formed on a surface of said refracting lens, said kinoform lens transmitting throughout said objective aperture a first diffracted portion of light and a second undiffracted portion of light, said first diffracted portion of light from said second distance diffracted by said diffraction lens in an amount for said refracting lens to focus said first diffracted portion of light from said second distance onto said input screen of said light intensifier, and said second undiffracted portion of light from said first distance being focused solely by said refracting lens onto said input screen of said light intensifier.

17. The multi-focus low light vision apparatus as claimed in claim 16, whereby:

said first focusing means consists of a double convex refracting lens; and

said second focusing means includes a kinoform lens formed on a convex surface of said double convex refracting lens.

18. The multi-focus low light vision apparatus as claimed in claim 16, whereby:

said first focusing means consists of a plano-convex refracting lens; and

said second focusing means includes a kinoform lens formed on a planar surface of said plano-convex refracting lens.

19. The multi-focus low light vision apparatus as claimed in claim 11, whereby:

said first focusing means includes a refracting lens having a focal length for focusing light from the first distance onto said input screen of said light intensifier; and

said second focusing means includes a refracting birefringent lens having a predetermined focusing effect for light of a first polarity and essentially no focusing effect for light of a second polarity orthogonal to said first polarity, light of said first polarity from said second distance refracted by said predetermined focusing effect of said refracting birefringent lens in an amount for said refracting lens to focus light of said first polarity from said second distance onto said input screen of said light intensifier, and light of said second polarity being focused solely by said refracting lens onto said input screen of said light intensifier.

20. The multi-focus low light vision apparatus as claimed in claim 19, further comprising:

a polarizing filter disposed in tandem with said first and second focusing means having a polarizing filter axis rotatable between a position essentially aligned with said first polarity and a position essentially aligned with said second polarity for varying the proportion of light of said first and second polarities reaching said input screen of said light intensifier.

21. The multi-focus low light vision apparatus as claimed in claim 11, whereby:

said first focusing means includes a refracting birefringent lens having a first focal length for focusing light a first polarity from the first distance onto said input screen of said light intensifier and essentially no focusing effect for light of a second polarity orthogonal to said first polarity; and

said second focusing means includes a refracting birefringent lens having a second focal length for focusing light of said second polarity from the second distance onto said input screen of said light intensifier and essentially no focusing effect for light of said first polarity.

22. The multi-focus low light vision apparatus as claimed in claim 21, further comprising:

a polarizing filter disposed in tandem with said first and second focusing means having a polarizing filter axis rotatable between a position essentially aligned with said first polarity and a position essentially aligned with said second polarity for varying the proportion of light of said first and second polarities reaching said input screen of said light intensifier.

23. A retrofit apparatus for use with a low light vision apparatus having a first focusing system disposed in a first objective aperture for focusing light from a first distance onto the input screen of a light intensifier, the light intensifier for producing at an output screen a light intensified image of a light image impinging on the input screen, said retrofit apparatus comprising:

a second focusing means having a second objective aperture essentially the same as the first objective aperture and having essentially no spectral filtering, said second focusing means constructed whereby when disposed in tandem with the first focusing means a portion of light from a first distance passes through both said first and second focusing means and is focused thereby onto said input screen of said light intensifier and a portion of light from a second distance passes through both said first and second focusing means and is focused thereby onto said input screen of said light intensifier; and

a mounting means having said second focusing means disposed thereon, said mounting means mountable on the low light vision apparatus for disposing said second focusing means in the first objective aperture in tandem with the first focusing means.

24. The retrofit apparatus as claimed in claim 23, whereby:

said second focusing means includes a diffraction lens transmitting throughout said second objective aperture a first diffracted portion of light and a second undiffracted portion of light, said first diffracted portion of light from said second distance diffracted by said diffraction lens in an amount for the first focusing means to focus said first diffracted portion of light from said second distance onto said input screen of said light intensifier, and said second undiffracted portion of light from said first distance being focused solely by the first focusing means onto said input screen of said light intensifier.

25. The retrofit apparatus as claimed in claim 24, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth selected with regard to a predetermined wavelength for providing a predetermined proportion of said first diffracted portion of light and said second undiffracted portion of light.

26. The retrofit apparatus as claimed in claim 25, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth of one half said predetermined wavelength for providing approximately equal proportions of received light in said first diffracted portion of light and said second undiffracted portion of

27. The retrofit apparatus as claimed in claim 25, whereby:

said diffraction lens of said second focusing means consists of a kinoform lens having a depth of one fifth said predetermined wavelength for providing approximately 20% of received light in said second undiffracted portion of light.

28. The multi-focus low light vision apparatus as claimed in claim 23, whereby:

said second focusing means includes a refracting birefringent lens having a predetermined focusing effect for light of a first polarity and essentially no focusing effect for light of a second polarity orthogonal to said first polarity, light of said first polarity from said second distance refracted by said predetermined focusing effect of said refracting birefringent lens in an amount for the first focusing means to focus light of said first polarity from said second distance onto said input screen of said light intensifier, and light of said second polarity being focused solely by the first focusing means onto said input screen of said light intensifier.

29. The retrofit apparatus as claimed in claim 28, further comprising:

a polarizing filter disposed on said mounting means in tandem with said second focusing means having a polarizing filter axis rotatable between a position essentially aligned with said first polarity and a position essentially aligned with said second polarity for varying the proportion of light of said first and second polarities reaching said input screen of said light intensifier.