Due to the high dependence of our thermal emission characteristics on the wavelength of the heat source due to the extreme dependence of our thermal emission behavior on the wavelength, only certain wavelengths are suitable for thermal measurements. The following graphs show the thermal transmission range of common thermal lenses and window substances for infrared thermometers. The blue-colored curve is the general rule that applies to all materials. It is the average value over a temperature range of zero (black), infinity (green) and 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 material in relation to the thermal gradient. This ratio is calculated as a function the temperature variation along a viewing angle for a given viewing angles and 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 change from linear to spherical. The focal length of a system is also an important factor in the slope. This is thought of as a function the focal length divided by the length of the curve (i.e. the interval between shots).
The inside temperature of the system will be 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 for the thermal conductance of a glass bead inside a glass vial that has an opening in it can 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 system’s surface temperature and the curve of variation must remain constant. If the aperture is adjustable, then the curve may be curved because of the variation in the temperature of the glass used in the making of the bead and the temperature of the ambient air that is on the inside of the vial’s surface, and the focal length and time of shooting. A signature left by an artist on a flower is an example of a curly surface.
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 hot for the lens, then the outside surface temperature of the frame will be cooler and the interior temperature of the lens will be too hot. When the outside temperature of the lens and the frame are equally, then the frame will not require any adjustment to counteract the heating or cooling effects 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 there is no external cause of temperature variations impacts the system. However, if the system is mounted at a location with an obstruction or restricted view of the nearby building or scenery the internal temperature may require to be controlled.
The first mechanical interlocking system that was used to attach lenses to cameras were made out of plastic. This design was later used for pinhole glasses. A problem with this type of lens assembly is that the mechanical joints between the lens and frame could indent or even break. If this were to happen, happening, it would be necessary for the entire assembly to be replaced in the shortest amount of time. This is why this system is being replaced with more durable designs.
Pinhole glasses lenses are generally constructed using a frame of metal and a thin, plastic or glass lid. These lense designs must at the very minimum have a hermetically-sealed construction. A lens that is hermetically sealed has an enclosed surface at the bottom and the top. The top surface could contain a mechanical seal similar to that previously mentioned. It could also include an lip, adhesive, or layer of plastic film.
A lens surface that is an adhesive and is bonded to the base is an additional embodiment of this type lens and window assembly. This kind of system usually consists of a casing for windows and a series of compartments for lenses. The windows may also contain different 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 there are a number of compartments that could house the temperature control as well as a range of other devices, like an alarm clock or thermostat.
This is not an exhaustive list of all types of lens assemblies and windows. However, it is indicative of the important technologies associated with this invention. Please refer to the entire disclosure for more information. Refer to the sections that pertain to “details about the present invention” and “Description Of the Process With Respect To the Identification of the various classes of products which are involved in the Present Application.”
know more about ZnSe lens and window here.