Optical: systems and elements – Having significant infrared or ultraviolet property – Lens – lens system or component
Reexamination Certificate
1999-06-25
2001-09-18
Henry, Jon (Department: 2872)
Optical: systems and elements
Having significant infrared or ultraviolet property
Lens, lens system or component
C359S565000, C359S019000
Reexamination Certificate
active
06292293
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to infrared imaging systems. More particularly, the present invention relates to a wide-angle infrared lens having an internal aperture stop.
BACKGROUND
Infrared imaging is the process of detecting infrared radiation and producing an image capable of being visualized by the human eye. A typical infrared imaging system includes a number of lenses, a chopper, an infrared detector, signal processing electronics, and a display.
One problem found with prior art infrared imaging systems relates to the intensity of the infrared radiation. This problem is particularly evident in wide-angle infrared imaging systems used in extreme environments. For example, in fire-fighting applications, the intensity of infrared radiation from very hot or burning objects is sometimes great enough that it saturates the infrared detector. It is, therefore, desirable to reduce the intensity of the infrared radiation when needed without adversely effecting image quality.
Prior wide-angle infrared imaging systems have used two to three Germanium (Ge) lenses and have used an external entrance pupil or aperture stop. One example of such a prior wide-angle system having an external entrance pupil is illustrated in U.S. Pat. No. 5,479,292 issued to Yoshikawa et al. In particular, such prior design have typically used an external entrance pupil or aperture stop with a negatively powered Ge lens follow by one or two positive powered Ge lenses. The use of external entrance pupils, however, is often undesirable, for example, in extreme conditions such as in fire-fighting applications. If the entrance pupil is external, the pupil cannot be sealed off without a significant increase in the size and cost of the infrared imaging system. Other prior designs that do not use external entrance pupils have made use of three or more optical elements. However, such designs typically have had poorly defined entrance pupils that are not adequate for the full processing range desired.
SUMMARY OF THE INVENTION
In accordance with the present invention, an infrared lens and detector system and associated method are disclosed that utilize infrared lenses to form an internal entrance pupil at which an internal aperture stop may be placed to control the intensity of infrared radiation focused on the infrared detector. The present invention thereby allows for size, cost and performance advantageous that have not previously been attained.
In a first embodiment, the present invention is an infrared lens assembly including a first infrared lens, a second infrared lens spaced from the first lens to form a pupil between the first and second lenses, and an aperture stop disposed proximal the pupil. In more detailed respects, the present invention may form a wide-angle lens having a view angle of about thirty degrees or greater and may include only two lenses. In addition, the lenses may be aspheric, and the surface of the second lens facing the pupil may be covered with a diffractive surface to reduce color aberrations.
In further respects, the aperture stop may have a fixed diameter or may have an adjustable diameter. In particular, the range for the adjustable diameter may provide for stops from about F/1 to F/10. Still further, the aperture stop may be manually or automatically adjustable depending upon an intensity of the infrared radiation coming from the received image. The lens assembly may also be sealed allowing for better performance in extreme environmental conditions.
In another embodiment, the present invention is an infrared lens detector system including an infrared detector, a first and second lenses disposed in front of the infrared detector such that the second lens being spaced from the first lens to form a pupil between the first and second lenses and to focus infrared radiation onto the infrared detector, and an aperture stop positioned between the first and second lenses at the pupil. In addition, the detector system may further include a signal processor coupled to the infrared detector and a display coupled to the signal processor. The detector system may also be sealed. In one particular aspect, the detector system is operable for a fire-fighting application.
In yet another respect, the present invention is a method for controlling an intensity of infrared radiation passing through an infrared lens including providing a first and second lenses, positioning the first and second lenses to form a pupil between the first and second lenses and to focus infrared radiation passing through the first and second lenses, and controlling the intensity of the infrared radiation passing through the first and second lenses by positioning an aperture stop proximate the pupil. In addition, the method may further include detecting the infrared radiation passing through the first and second lenses. Further, the method may include processing the detected infrared radiation and displaying an image resulting from the processing infrared radiation. Still further, the method may include adjusting the diameter of the aperture stop to modify the amount of infrared energy passing through the first and second lenses and this adjusting step may include automatically adjusting the diameter of the aperture stop depending upon an intensity of the infrared radiation.
REFERENCES:
patent: 3360649 (1967-12-01), Brau et al.
patent: 4542954 (1985-09-01), Stoltzmann
patent: 4738496 (1988-04-01), Canzek
patent: 5051591 (1991-09-01), Trotta et al.
patent: 5251063 (1993-10-01), Baumann
patent: 5386315 (1995-01-01), Amon et al.
patent: 5479292 (1995-12-01), Yoshikawa et al.
patent: 5737120 (1998-04-01), Arriola
patent: 5880879 (1999-03-01), Foo
patent: 5909307 (1999-06-01), Koyama
Grossman Rene' E.
Henry Jon
O'Keefe Egan & Peterman, LLP
Raytheon Company
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