Due to the high dependence of our thermal emission behavior on the thermal wavelength, only certain wavelength ranges are suitable for measurements of thermal. The following figures show the range of thermal transmission for common thermal lenses and window materials for infrared thermometers. The blue-colored curve illustrates the general rule applicable to all materials and shows the average value over an interval of temperature from zero (black) to infinity (green) which is the cold-pressure limitation (CPL).
For windows and lenses the cold-pressure limit is defined as the highest value of the damping ratio of a material against the thermal gradient. This ratio is calculated as a function of the temperature difference along the viewing angle for given viewing angles and cte of a window or lens. The slope of this curve is proportional to the bending force of an entire system, which is the result when the angle of incidence shifts from spherical to linear. The slope of this curve is also proportional to the focal length of the system, which can be described as an expression of the focal length divided by the period of the curve (i.e. the period between shots).
The inside temperature of the system will always remain within the prescribed curve for a particular temperature and focal length of a window assembly or lens. This is also known as a “curved top”. For instance the curve of thermal conductance of a glass bead inside a glass vial with an opening in it can be plotted in relation to the focal length, the temperature difference inside the vial between the bottom of the bead and its surface, and the angle of incidence for a particular window assembly. 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 must remain the same. If the aperture is adjustable this means that the curve could be curved as a result of the variation in the temperature of the glass used to create the bead, the temperature of the ambient air that is on the inside surface of the vial and the focal length and time of shooting. A signature left by a photographer on the petals of a flower is an example of a curly surface.
A lens and window must be mounted in a way that their focal points and lines of sight are properly aligned. If the interior surface temperature of a system is too cold for the lens, then the outside temperature of the frame and the interior temperature will be too high. If the temperature outside of the lens and the frame are equally and the frame is at the same temperature, it will not require any adjustments to counteract the effects of heating or cooling of internal temperature differences. The internal temperature of the system will be appropriate for a particular focal length without the need for any other adjustments, provided that there is no external source of temperature fluctuations affects the system. If the system is located in an area with restricted or unobstructed 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 from 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 could indent or even break. In the event of this happening, it will be required for the entire assembly to be replaced in the shortest amount of time. Due to this the type of system has been replaced with more robust designs.
Lenses made to be used with pinhole glasses usually have a metallic frame and a thin glass or plastic lid. These lense designs should at the very minimum have a hermetically sealed construction. A hermetically sealed lens construction contains a sealed surface along the bottom and top of the lens assembly. The top layer could have a similar seal similar to that mentioned earlier. It could also be a source of adhesive, lip, or layer of plastic film.
Another variation of window and lens assembly is to have the lens surface, which is an adhesive that adheres to the base of the window assembly. This system usually consists of a glass casing and a series lens compartments. The windows can also house other kinds of devices, like light emitters or thermometers. This kind of system could also include a thermostat or light emitter that regulates the temperature of the room. In this case there are a number of compartments that could house the temperature control along with a number of other devices, such as an alarm clock or thermostat.
This isn’t an exhaustive list of all the types of window and lens assemblies. It’s a good indication of the most important technologies that are related to this invention. For more information, please see the entire disclosure. Refer to the sections on “details about the invention” and “Description of the Method with Regard to the Identification of the various classes of products which are involved in the Present Application.”
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