Due to the extreme dependence of our thermal emission behaviour on the wavelength of the thermal radiation, only certain wavelength ranges are suitable for measurements of thermal. The following graphs show the ranges of thermal transmission of common window and thermal lenses for infrared thermometers. The blue-colored curve shows the general rule for all materials, and represents the average value for a temperature interval of zero (black) to infinity (green) which is known as the cold-pressure limit (CPL).
The cold-pressure limit, which is used to determine the thickness of windows and lenses, is the maximum measured value of a material’s damping coefficient against the thermal gradient. This ratio is calculated as a function of the temperature variation in relation to the viewing angle for a given viewing angle and cte of the lens or window. The bending moment of a system is the change in angle of incidence from linear or spherical. This results in the slope being proportional to this curve. The slope of this curve is also proportional to the focal length of a system, which can be considered as an expression of the focal length divided by the duration of the curve (i.e. the period between shots).
The temperature of the inside of the system will always remain within the prescribed curve for the given temperature and focal length of a window assembly or lens. This is also referred to as a “curved top”. The thermal conductance curve of a glass beads within a glass vial can be plotted as a function of the focal length as well as the temperature difference between the bottom and the vial’s surface and the angle of incidence of a specific window. If the aperture is fixed for all shots, then the area between the system’s surface temperature and the curve of variation should remain constant. If the aperture is variable this means that the curve could be curved as a result of the fluctuation in the temperature of the glass used to create the bead, the temperature of the ambient air that is on the inside of the vial’s surface, and the focal length and duration of shooting. A typical example of a curly surface can be seen in the signature of the photographer of flowers.
The mounting of a window and lens should be done in a way that their focal points, and lines of sight, are in the correct direction. If the interior surface temperature of an object is too cold for the lens, then the outside temperature of the frame and its interior temperature will be too high. The frame will not need to be adjusted to compensate for internal temperature fluctuations or cooling effects. If there are no temperature differences from outside, the system’s inside surface temperature will be the same for the given focal length. If the system is located in an area with limited or obstructed views of surrounding structures or landscape it could be necessary to regulate the internal temperature.
The first mechanical interlocking systems that were used to mount lenses to cameras were constructed of plastic or other materials that would be able to bend or form according to changes in mounting pressure. This design was later adopted for use with pinhole glasses. This type of lens assembly is not without a problem: the mechanical joints between the lens and frame might break or become indented. If this were to happen then it is required to replace the entire system within a short amount of time. Because of this, this type of system has been replaced by more robust designs.
Pinhole glasses lenses are generally made with a metal frame and a thin, plastic or glass lid. The lense designs should at a minimum, be hermetically sealed. A hermetically sealed lens construction includes a sealed surface at the top and bottom of the lens assembly. The top surface could contain an electronic seal similar to the one previously mentioned. It could also include an adhesive, lip or a layer of plastic film.
A lens surface that contains a substrate and adheres to the base is an additional example of this type of window and lens assembly. This kind of system typically consists of a window casing and several lens compartments. The windows could also include other kinds of devices, like light emitters or thermometers. This kind of system could include a thermostat or light emitter that regulates the temperature in the room. In that case the system would comprise of compartments that could house the temperature controller along with a number of other devices, such as an alarm clock or thermostat.
This is not a full listing of all the types of window assemblies and lenses that are available. It’s an indication of the significant technologies that are connected to this invention. For more information, look over the entire disclosure. In particular, please take a look at the sections relating to “details of the present invention” and “Description of the Method with Regard to the Identification of the Different types of products involved in the Present Application.”
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