Patent Application
20090091821
The field of present disclosure relates to optical sighting devices such as spotting scopes, riflescopes, binoculars, monoculars, and optical protection systems and devices therefore.
Lasers are increasingly found in various military, law enforcement and hunting applications for range finding, tactical illumination (e.g., aiming) and target designation. The human eye, as well as optical sensors/detectors and photo receptors can be damaged by exposure to high intensity light. For example, the retina of the eye and the nearby nerves may be damaged when exposed to a laser beam for only a short time. The irradiance of the laser energy perceived by the eyes, and hence the potential for eye damage, is increased when a user employs a spotting scope, binoculars or similar visual telescopic instrument because the laser light is focused by these magnification devices and thus a greater intensity of such laser light reaches the eyes. The present inventor has recognized the potential hazard of using a spotting scope or other optical devices where an intense laser radiation is present.
Current laser eye protection methods for visual optics involve placing a filter for attenuating the intensity of laser wavelength light from the visible wavelengths in the optical path of the optics. These filters are placed either in front of or just behind the objective lens of the optics and are either reflective or absorptive filters or an optic with an ablative coating. The present inventor has determined that visible light transmission through either type of filter is typically reduced by more than 10 percent, and with light transmission loss through a typical high-quality observation or targeting device, there is an additional 10 percent loss. Therefore a combined loss of greater than 20 percent would be experienced in that approach.
The present invention is directed to optical sighting devices. In a preferred embodiment, the optical sighting device includes optics that direct the desired visible wavelength light to the eye or other sensor/detector while removing certain undesirable wavelengths such as IR or UV. A preferred configuration may utilize a spotting scope having two front surface mirrors that fold the optical path to offer greater magnification and performance in a compact housing. This two mirror spotting scope is modified by replacing one or both of the mirror surfaces with a band pass mirror, known as a cold mirror, having particular optical transmission/reflection properties to reflect visible light and pass the undesirable wavelengths.
Preferred embodiments will now be described with reference to the drawings. The preferred embodiments will be described in terms of a lens system for a spotting scope, but alternate embodiments may be employed within binoculars, monoculars, riflescopes and other types of optical viewing mechanisms.
In this lens assembly 10, one or both of the mirrors 34, 36 is replaced with a cold mirror, a dichroic reflector which functions as a broadband interference optic. In a preferred configuration, the cold mirror 34 includes a glass plate or other substrate coated on its front surface with a dielectric film stack. The cold mirror optic is selected to have specific optical properties to (1) reflect the visible light spectrum and (2) pass light of certain near infrared and infrared (IR) wavelengths. The cold mirror 34 reflects virtually all the visible light spectrum while allowing the specific near IR and IR spectrum light to pass through. The typical reflectivity of a cold mirror for visible light is about 96%, which yields a 4% loss in intensity. In contrast, a band pass filter located within the optical path to remove infrared light would typically introduce a 10% loss in the intensity of the visible light passing through the optical system.
A cold mirror may be defined by its transmissive and reflective properties.
In an alternate configuration, both mirror 34 and mirror 36 may comprise cold mirrors. In such a configuration, the intensity loss will be somewhat higher than the single cold mirror combination. For example, presuming a 4% loss in the visible light wavelength, combined reflectivity would be 96%×96%=92.16%. However, by providing the reflective surfaces of both mirrors 34 and 36 being cold mirrors, combined reflectivity for IR wavelength light would be 15%×15%=2.25%. Thus for the dual cold mirror system, on the order of 97.75% of the IR light is prevented from reaching the ocular 80 via operation of the two cold mirrors 34, 36.
In the dual cold mirror configuration, the mirrors 34, 36 may comprise the same or similar dielectric coatings or each mirror may comprise a different coating having unique optical properties or reflectivity frequency response. For example, one of the mirrors may effectively remove IR wavelength light (e.g., 85% transmissive) at 725 nm +/−5 nm while the other mirror may effectively remove IR wavelength light (e.g. 85% transmissive) at 750 nm ±5 nm. In another example, one mirror may have a lower removal percentage in a band at a particular wavelength as in the following table:
Thus by way of two mirrors, the Mirror A compensates for the removal deficiency of Mirror B at the 750 nm band and Mirror B compensates for the removal deficiency of Mirror A at the 725 nm wavelength band whereby in excess of 90% of IR light intensity is removed at each of the 725 nm and 750 nm wavelength bands. Thus by a combination of cold mirrors, a high range (greater than 90%) or ultra high range (greater than 95%) of IR light across the IR spectrum may be removed.
The coating is selected/designed depending upon several factors, including: mirror materials, the angle of incidence θi, and the wavelengths of the light desired to be removed.
In a preferred single cold mirror configuration, it is preferred that the cold mirror transmit (and thus remove from the optical path) at least 70% or 80% of IR light from 725 nm to 1200 nm (or 750 nm and 1100 nm). Some of the common laser devices applications include: YAG laser (1500 nm and 1064 nm) typically used in military vehicle applications; and laser diodes (905 nm and 808 nm) typically used for laser rangefinder applications. By removing the IR light of this wavelength range, laser light produced by these laser devices is removed.
The roof prism 130 illustrated in
Other types of prisms may be employed with dielectric coatings on certain surfaces to serve as a cold mirror. A Porro prism may have two reflective surfaces that may accommodate a dielectric coating. A double Porro prism may have four reflective surfaces suitable for dielectric coating. An Abbe-Koenig prism may have two reflective surfaces for dielectric coating. An Amici prism is another type of roof prism having one reflective surface that may be suitable for dielectric coating.
The undesirable IR wavelength light that is transmitted through the cold mirror is preferably routed to a black body behind the cold mirror, the black body designed to absorb or trap the IR light. Since the IR light is likely not to be a sustained pulse, it is expected that the total energy of the IR radiation will be somewhat low and thus should not generate significant heat.
Thus preferred optical systems and configurations have been shown and described. While specific embodiments and applications for have been shown and described, it will be apparent to one skilled in the art that other modifications, alternatives and variations are possible without departing from the inventive concepts set forth herein. Therefore, the invention is intended to embrace all such modifications, alternatives and variations.
This application claims priority to provisional application No. 60/978,713 filed Oct. 9, 2007, hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60978713 | Oct 2007 | US |
