Due to the high dependence of our thermal emission behavior on the wavelength of the thermal radiation, only certain wavelength ranges are suitable for thermal measurements. The following diagrams illustrate the thermal transmission ranges of common thermal lenses and window materials for infrared thermometers. The blue-colored curve represents the general rule for all materials. It is the average value across the temperature range from zero (black) and infinity (green) and is the cold pressure limit (CPL).
The cold-pressure limit, which is used to determine the thickness of windows and lenses is the highest recorded value of a material’s damping rate against the thermal gradient. This ratio is calculated as a function of the temperature differential across the viewing angle for a given viewing angle and cte for the window or lens. The slope of the curve is proportional to the bending moment of a system, which occurs when the angle of incidence changes from spherical to linear. The focal length of a system is also an element in the slope. This can be thought of as a function of the focal length divided by the length of the curve (i.e. the time between shots).
For a given temperature range and a given focal length of a lens or window assembly, the inside temperature of the system will always be within the prescribed range in the perfect order called a “curved surface.” The thermal conductance curve of a glass bead inside a glass vial could be plotted as a function the focal length, the temperature difference between the bottom of the vial and its surface and the angle of incidence of a specific window. If the aperture is fixed for all shots, then the area between the surface temperature of the system and the curve of variation for the particular window assembly should always remain the same. Variable apertures can cause the curve to become curvilinear due to changes in the glass’s temperature used to create the bead as well as the ambient air temperature, focal length, and time of photography. A signature left by an artist on the petals of a flower is an example of a curly surface.
A window and lens must be mounted in a way that their focal points and lines of sight are correctly aligned. If the interior surface temperature of a system is too cold for the lens, the exterior temperature of the frame and its interior temperature will be too high. If the temperature outside of the lens and the frame are equally, then the frame will not require any adjustments to compensate for the heating or cooling effects of internal temperature variations. The inside temperature of the system will be appropriate for a given focus length without the need for any other adjustments, provided there is no external cause of temperature fluctuations affects the system. If the system is located in an area that has limited or obstructed views of the surrounding structures or landscape it might be necessary to control internal temperatures.
The first mechanical interlocking system used to attach camera lenses were made of plastic. This design was later used to create pinhole glasses. The issue with this kind of lens assembly is that the mechanical joints between the frame and lens may indent or break. If this happens the result is necessary to replace the entire assembly within a short amount of time. Due to this the system has been replaced by more robust designs.
Pinhole glasses lenses are usually made with a metal frame and a thin, plastic or glass lid. At a minimum the lense designs should have a hermetically sealed lens construction. A hermetically sealed lens has a sealed surface on the bottom and at the top. The top surface could contain an elastomeric seal similar to the one previously mentioned. It could also contain another substance, such as an adhesive, a lip, or a layer of plastic film.
A lens surface that has an adhesive and is bonded to the base is an additional embodiment of this type window and lens assembly. This type of system is typically comprised of a casing for windows and a series of lens compartments. Other types of devices could be used in the windows, like light emitters and thermometers. In certain instances, the device that controls the temperature in the room could also be part of this type of system. In this case there are a number of compartments that could house the temperature controller as well as a range of other devices, including an alarm clock or thermostat.
This is not an exhaustive list of all kinds of window and lens assemblies. It’s an indication of the most important technologies that are related to this invention. For more information, please see the entire disclosure. In particular, please read the portions relating to “details of the Present Invention” and “Description of the Method with Respect to the Identification of the Different Classes of Products That Are Involved in the Present Application.”
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