Due to the high dependence of our thermal emission characteristics on the thermal wavelength that we have, only certain wavelengths are effective for thermal measurements. The following diagrams illustrate the range of thermal transmission 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 across the temperature range of zero (black) to infinity (green) and that is the cold pressure limit (CPL).
For lenses and windows The cold-pressure limit can be defined as the highest value of the damping ratio of a material against the thermal gradient. This ratio is plotted as a function of the temperature differential along the viewing angle for a particular viewing angle and cte of the lens or window. The bending moment of a system is the change in angle of incidence from spherical or linear. This results in the slope being proportional to this curve. The slope of this curve is also proportional to the focal length of the system, which is considered as an expression of the focal length divided by the length of the curve (i.e. the interval between shots).
For a set of temperature and a given focal length of a lens or window assembly, the inside temperature of the system will always fall within the prescribed curve in the perfect order known as a “curved surface.” For instance, the curve for the thermal conductance of a glass piece inside a glass vial that has holes in it could be plotted as a function of 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 area between the inside surface temperature of the system and the curve of variation for that particular window assembly should always remain constant. Variable apertures can cause the curve to become curvilinear due to variations in the glass’s temperature used to make the bead, ambient air temperature, length of the lens, and time of photography. An example of a curved surface can be seen in the signature left by a photographer of flowers.
A window and lens should be mounted so that their focal points and lines of sight are properly aligned. If the inside surface temperature of the system is too cold for the lens, then the outside surface temperature of the frame will be lower and the inside of the lens will be too hot. The frame will not need to be adjusted in order to compensate for internal temperature fluctuations or cooling effects. If there are no temperature differences from outside, then the system’s internal temperature will be the same for the given 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 control the internal temperature.
The first mechanical interlocking systems that were used to attach lenses to cameras were made of plastic or other materials that would change shape or bend in response to changes in mounting pressure. 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 lens could indent or even break. If this happens the result would be necessary to replace the entire assembly within a short amount of time. Due to this the type of system has been replaced with more robust designs.
Pinhole glasses lenses are generally constructed with a frame made of metal and a thin, plastic or glass lid. The lense designs should at a minimum have a hermetically-sealed construction. 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 elastomeric seal similar to that described above. It could also contain some other substance, for instance, an adhesive, lip, or a layer of plastic film.
A lens surface that contains an adhesive and is bonded to the base is another example of this type of window and lens assembly. This system usually consists of a glass casing and a series of lens compartments. Other kinds of devices can be used in the windows, like thermometers and light emitters. In certain instances, the device that controls the temperature within the room could also be part of this type of system. In this case the system would comprise 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 is not an exhaustive list of all the types of lens assemblies and windows. It is indicative of the important technologies related to this invention. Please refer to the entire disclosure for more information. In particular, please read the portions relating to “details of the Present Invention” and “Description of the Process with Regard to the Identification of the Various classes of products involved in the Present Application.”
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