Due to the high dependence of our thermal emission behaviour on the thermal wavelength, only certain wavelength ranges are suitable for thermal measurements. The following figures reveal the range of thermal transmission of standard thermal lenses and window materials for infrared thermometers. The blue-colored curve shows the general rule for all materials and shows the average value across a temperature interval of zero (black) to infinity (green) that is the cold-pressure limit (CPL).
For windows and lenses, the cold-pressure limit is defined as the highest value of the damping ratio of a substance against the thermal gradient. This ratio is plotted as a function of the temperature variation across the viewing angle for a given viewing angle and cte of the window or lens. The bending moment of an object is the change in angle of incidence from linear or spherical. This makes the slope proportional to this curve. 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).
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 fall within the prescribed curve in a perfect regularity called a “curved surface.” For instance, the curve for the thermal conductance of a glass bead inside a glass vial with holes in it could be plotted in relation to the focal length and the temperature difference within the vial between the bottom of the bead and the vial’s surface, and the angle of incidence for a specific window assembly. If the aperture is fixed for all shots, then the space between the surface temperature of the system and the curve of variation for that particular window assembly must remain the same. If the aperture is variable and the curve is not fixed, then it could be curved because of the fluctuation in the temperature of the glass used to make the bead as well as the temperature of the ambient air that is on the inside of the vial’s surface, and the focal length as well as the duration of shooting. An example of a curved surface can be seen in the signature left by the photographer of the flower.
The mounting of a window and lens should be done in a way that their focal points, and lines of view, are in the correct direction. If the surface temperature of an object is too cold for the lens, the outside temperature of the frame as well as the interior temperature will be too high. The frame will not have to be adjusted to compensate for internal temperature variations or cooling effects. The internal temperature of the system will be appropriate for a specific focal length without the need for any other adjustments, provided there is no external source of temperature variations affects the system. However, if the camera is mounted at a location with an obstruction or limited view of any surrounding scenery or building and the surrounding area, then internal temperatures might require to be controlled.
The first mechanical interlocking system that was used to mount lenses to camera were made out of plastic. This technology was later adopted for use with pinhole glasses. One issue with this type of lens assembly is that the mechanical joints between the frame and the lens might indent or even fracture. If this should be happening, it will be essential for the entire system to be replaced within a short time. Because of this issue the 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. These lense designs should at a minimum, be hermetically sealed. A hermetically sealed lens construction has a sealed surface on the bottom and top of the lens assembly. The top layer could be a part of an electronic seal similar to that described above. It could also contain some other substance, such as an adhesive, a lip, or a layer of plastic film.
A lens surface that is the substrate and is attached to the base is an additional illustration of this kind of window and lens assembly. This type of system usually consists of a casing for windows and several lens compartments. Other types of devices could be integrated into the windows, like light emitters and thermometers. This type of system could also include the thermostat or light emitter that regulates the temperature of the room. In this case there are a number of compartments that could be used to house the temperature controller as well as a range of other devices, such as an alarm clock or thermostat.
This isn’t a complete list of all kinds of window assemblies and lenses that are available. However, it is indicative of the key technologies associated with this invention. For more information, please read 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 Respect to the Identification of the Different classes of products Included in the Present Applica.”
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