Due to the extreme dependence of our thermal emission behavior on the thermal wavelength that we have, only certain wavelengths are effective for thermal measurements. The following graphs show the range of thermal transmission for common thermal lenses and window materials for infrared thermometers. The blue-colored curve represents the general rule that applies to all materials. It is the average value over a temperature range of zero (black) to 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 measured value of a material’s damping rate against the thermal gradient. This ratio is calculated as a function of the temperature difference along the viewing angle for given viewing angle and the cte of a lens or window. The slope of this curve is proportional to the bending moment of the system, which happens when the angle of incidence changes from spherical to linear. The slope of this curve is also proportional to the focal length of a system, which is considered as a function of the focal length divided by the length of the curve (i.e. the interval between shots).
For a set of temperatures and a certain focal length of a window or lens assembly, the inside surface temperature of the system will always be within the prescribed curve , in the perfect order known as a “curved surface.” For instance the curve of thermal conductance of a glass bead inside a glass vial having an opening in it can be plotted in relation to the focal length and the temperature difference inside the vial between the bottom of the bead and the vial’s surface, and the angle of incidence for a given window assembly. If the aperture is fixed for all shots, then the area between the system’s surface temperature and the curve of variation will remain the same. Variable apertures can cause the curve to become curvilinear due to changes in the temperature of glass used for creating the bead as well as the ambient air temperature, the focal length, and the time of photography. A typical example of a curly surface can be seen in the signature of the photographer of a flower.
A window and lens should be mounted in a way that their focal points and lines of sight are correctly aligned. If the interior surface temperature of the system is too cold for the lens, the outside temperature of the frame as well as the interior temperature will be too high. The frame won’t need to be adjusted in order to compensate for internal temperature variations or cooling effects. If there are no temperature differences from outside, the frame’s inside surface temperature will be the same for a particular focal length. If the system is located in an area with restricted or unobstructed views of surrounding buildings or scenery it might be necessary to regulate the internal temperature.
The first mechanical interlocking systems used to attach lenses to cameras were constructed of plastic or other materials that would change shape or bend depending on changes in mounting pressure. This innovation was later adopted for use with pinhole glasses. This type of lens assembly has a problem with the mechanical joints that connect the frame and lens could crack or indent. If this should be happening, it would be essential for the entire system to be replaced within the shortest amount of time. This is the reason why this system is being replaced with more robust designs.
Pinhole glasses lenses are typically constructed using a frame of metal and a thin, glass or plastic lid. The lense designs should at a minimum, be hermetically sealed. A lens that is hermetically sealed has an enclosed surface at the bottom and at the top. The top layer could have a similar seal to the one described above. It could also be a source of lip, adhesive, or layer of plastic film.
Another embodiment of this type of window and lens assembly is an lens surface that is a substratethat is attached to the base of the window assembly. This kind of system is typically comprised of a casing for windows and several lens compartments. Other kinds of devices can be integrated into the windows, such as thermometers and light emitters. In some cases, the device used to control the temperature within the room could also be part of this type of system. A series of compartments could be used to house the temperature controller as well as a variety of other devices like an alarm clock, thermostat, or other devices.
This isn’t a complete list of all kinds of window assemblies and lenses that are available. However, it is indicative of the most important technologies that are related to this invention. Please read the entire disclosure for more details. Refer to the sections relating to “details about the present invention” and “Description of the process with Regard to the Identification of the Different Classes of Products which are involved in the Present Application.”
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