Due to the dependence of our thermal emission characteristics on the thermal wavelength because of the dependence of our thermal emission on the wavelength, only certain wavelength ranges are suitable for thermal measurements. The following graphs show the thermal transmission ranges of common thermal lenses and window materials for infrared thermometers. The blue-colored curve reflects the general rule that applies to all materials. It is the average value over a temperature range of 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 ratio against the thermal gradient. This ratio is calculated as a function the temperature difference across the viewing angle for given viewing angle and the cte of a window or lens. The slope of this curve is proportional to the bending angle of a system, which occurs when the angle of incidence shifts from linear to spherical. The focal length of an entire system is also an important factor in the slope. It can be thought of as a function the focal length divided by the length of the curve (i.e. the duration between shots).
The temperature of the inside of the system will always remain within the prescribed curve for a given temperature and the focal length of the window assembly or lens. This is also referred to as a “curved top”. For instance, the curve for the thermal conductivity of a glass beads inside a glass vial with an opening in it can be plotted as a function of 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 particular window assembly. If the aperture is fixed for all shots, then the space between the temperature of the inside surface of the system and the curve of variation for the particular window assembly must remain the same. If the aperture is adjustable, then the curve may be curved as a result of the variation in the temperature of the glass used to make the bead, the temperature of the ambient air that is on the inside surface of the vial, and the focal length as well as the duration of shooting. A signature left by a photographer on the petals of a flower is an example of a curving surface.
The mounting of a window and lens must be done to ensure that their focal points, and lines of sight are in the correct direction. If the internal temperature of the system is too cold for the lens, then the outside surface temperature of the frame will be lower and the interior temperature of the lens will be too hot. If the outside temperature of the lens and the frame are the same, then the frame will not require any adjustment to compensate for the heating or cooling effects of internal temperature differences. If there aren’t any temperature differences from outside, the system’s inside surface temperature will be the same for a particular focal length. If the system is located in an area that has restricted or blocked views of surrounding scenery or buildings it might be necessary to regulate the internal temperature.
The first mechanical interlocking system used to attach lenses to cameras were made out of plastic. This design was later adopted to work with pinhole glasses. This type of lens assembly comes with a drawback: the mechanical joints between the lens and frame might break or become indented. If this were to happen, then it would be necessary to replace the entire unit in a relatively short amount of time. Because of this issue the type of system has been replaced with more robust designs.
Lenses made to be used with pinhole glasses typically have a metallic frame and an elongated glass or plastic lid. At the very least, these lense designs should have a hermetically sealed lens construction. A hermetically sealed lens construction has an enclosed surface at the bottom and the top. The top surface may contain an elastomeric seal that is similar to that described above. It could also contain another substance, for instance, an adhesive, lip, or a layer of plastic film.
A lens surface that has a substrate and adheres to the base is a different example of this type of window and lens assembly. This system usually consists of a glass casing and a series lens compartments. Other types of devices could be used in the windows, like thermometers and light emitters. This type of system could also include a thermostat or light emitter which controls the temperature in the room. In this scenario there are a number of compartments that could house the temperature control together with a variety of other devices, like an alarm thermostat or clock.
This is not an exhaustive list of all the types of lens assemblies and windows. However, it is indicative of the key technologies associated with this invention. For more information, read the entire disclosure. Please refer to the sections on “details about the invention” and “Description of the Method with Respect To the Identification of the Different Classes of Products which are involved in the Present Application.”
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