Abstract: An optical apparatus for clearly viewing the interior of a containment vessel by applying a transpiration fluid to a volume directly in front of the external surface of the optical element of the optical apparatus. The fluid is provided by an external source and transported by means of an annular tube to a capped end region where the inner tube is perforated. The perforation allows the fluid to stream axially towards the center of the inner tube and then axially away from an optical element which is positioned in the inner tube just prior to the porous sleeve. This arrangement draws any contaminants away from the optical element keeping it free of contaminants. In one of several embodiments, the optical element can be a lens, a viewing port or a laser, and the external source can provide a transpiration fluid having either steady properties or time varying properties.

Abstract: A monitoring system for adjusting a light source for a counting cell signal in a counting and dispensing system, which light deteriorates over time as a result of dust accumulation from the handling of pills, capsules, and tablets. The monitoring system uses electronics to adjust the light relative to the dust accumulation, thus maintaining an accurate counting cell signal, so that the system can continue to function. In this respect, the monitoring system provides for longer intervals between required maintenance operations, and therefore reduces the cost of operation.

Abstract: A method and apparatus for maintaining a viewing window of a detector substantially clean includes enclosing the detector within a housing, and moving a target surface relative to the viewing window to create an airflow adjacent the viewing window. The housing can include an aperture through which the viewing window of the sensor views the target surface. Motion of the target surface creates an airflow velocity adjacent the viewing window for maintaining the viewing window substantially clean. To increase the accuracy of the detector, a high emissivity area is provided on an outside surface of the housing which faces the target surface.

Abstract: A shield is disclosed that is particularly useful for protecting exposed optical elements at the end of optical probes used in the analysis of hazardous emissions in and around an industrial environment from the contaminating effects of those emissions. The instant invention provides a hood or cowl in the shape of a right circular cylinder that can be fitted over the end of such optical probes. The hood provides a clear apertures through which the probe can perform unobstructed analysis. The probe optical elements are protected form the external environment by passing a dry gas through the interior of the hood and out through the hood aperture in sufficient quantity and velocity to prevent any significant mixing between the internal and external environments. Additionally, the hood is provided with a cooling jacket to lessen the potential for damaging the probe due to temperature excursions.

Abstract: A condensation free mirror to be used in a shower environment consisting of a mirror substrate and a means for detachably mounting the mirror to a shower wall. The mirror assembly is designed for optimum heat retention in order to provide a condensation free surface after being exposed to the warm shower stream. No internal plumbing, reservoirs, or anti-fog coatings are required to achieve a condensation free surface.

Abstract: A panoramic flash system is disclosed that filters out visible light (but not invisible light) from a flash unit that is directly connected to a camera equipped with a panoramic lens. The invisible light is then used to trigger a remote flash located in a blind spot of the field of view of the panoramic lens. The remote flash then illuminates the scene within the field-of-view of the panoramic lens. The visible-light filter can be an adhesive tape that is placed over the lens of a flash unit that is integral with the camera body. The panoramic lens can have the remote flash unit attached to the lens in the lens' blind spot.

Abstract: An air purge system for an optical sensor is disclosed. The air purge system includes a two sided lens having an optical sensor positioned on the first side and a fluid stream on the second side. The air purge system further includes, a plenum having an inlet, an array of parallel channels and an outlet, whereby the array of parallel channels, is disposed between the inlet and the outlet. The outlet is positioned on the second side of the housing and may be adapted to direct a fluid stream substantially parallel to the second side of the lens.

Abstract: An arrangement for cleaning the mirror element of an outside rear view mirror is disclosed. The arrangement includes a washing nozzle, which is disposed in the region of the outside rear view mirror on a motor vehicle and from which a jet of a cleaning liquid may be discharged. The position of the mirror element (1) relative to the body of the motor vehicle is variable, whereas the washing nozzle (9) is connected in a fixed manner to the body. To improve the cleaning action of the washing to nozzle (9), the mirror element (2) may be adjusted between a normal position, in which the driver may observe the traffic behind him in the mirror element (2), and a cleaning position, in which an advantageous angle for cleaning, in particular a steep angle arises between the mirror plane of the mirror element (2) and the jet of cleaning liquid.

Abstract: A laser based processing machine incorporates in the path of a laser beam (7) at least one optical element (1) which has a surface (5) situated in the path of the laser beam (7) and a scavenging medium delivery device which flushes its surface in an essentially counterflow-free fashion. The device includes a delivery element with flow nozzles about a portion of the periphery of the optional element and through which the scavenging medium flows onto the surface of the element and thereacross.

Abstract: A hydrophilic mirror comprising a glass substrate having on the main surface side thereof a layer having a refractive index n1 at 550 nm, a layer having a refractive index n2 at 550 nm, a tin oxide layer having a refractive index n3 at 550 nm, and an overcoat in this order, the refractive indices n1, n2 and n3 satisfying the relationship: n1≧n3>n2, and having a visible light reflectance of 70% or more.

Abstract: An ultraviolet optical device includes optical parts on which an ultraviolet ray is irradiated. Some or all of the optical parts are arranged in an envelope having a gas inlet port and a gas output port. In the envelope (9), a dry gas having an amount of moisture (as volume fraction) of 5,000 [ppm] or less and led from the gas inlet port (10) is sprayed on an optical part in which at least a deterioration in optical characteristics is especially a problem, so that an improvement in the secular change of the optical part can be achieved.

Abstract: A optical assembly (10) for directing and/or focusing a beam of light energy (11) for an exposure apparatus (28) is provided herein. The optical assembly (10) includes one or more optical sections (12) which are assembled together. At least one of the optical sections (12) includes an optical housing (14) having an inner wall (15) which defines a optical chamber (16). One or more optical elements (18) can be secured to the optical housing (14) of each optical section (12). Additionally, each optical section (12) can include a plurality of outlet ports (20) and a plurality of inlet ports (22) for purging the optical chamber (16). The inlet ports (22) and the outlet ports (20) are uniquely positioned to minimize the time required to purge the optical assembly (10) and the amount of replacement fluid (24) used to purge the optical assembly (10).

Abstract: A method and apparatus for maintaining a viewing window of a detector substantially clean includes enclosing the detector within a housing, and moving a target surface relative to the viewing window to create an airflow adjacent the viewing window. The housing can include an aperture through which the viewing window of the sensor views the target surface. Motion of the target surface creates an airflow velocity adjacent the viewing window for maintaining the viewing window substantially clean. To increase the accuracy of the detector, a high emissivity area is provided on an outside surface of the housing which faces the target surface.

Abstract: The invention concerns a method and device for automatic cleaning of opto-electronic measuring systems used in process-technology for the analysis of substances in liquids and gases by means of optical absorption and fluorescence. The method is characterized in that the soiling degree is detected by the opto-electronic sensor system itself and, with predetermined soiling degree, a cleaning liquid cleans the soiling-sensitive optical components and detects the residual soiling, which is then evaluated quantitatively and compensated for in the signal analysis.

Abstract: A personal shower mirror for attaching to a shower curtain pole or to a sliding glass shower door comprising a mirror element, a housing enclosing the mirror element, a hanging device and an extendable pole connected at one end to the housing and at the other threaded to receive the hanging device.

Abstract: A personal shower mirror for attaching to a shower curtain pole or to a sliding glass shower door comprising a mirror element, a housing enclosing the mirror element, a hanging device and an extendable pole connected at one end to the housing and at the other threaded to receive the hanging device.

Abstract: Provided are novel methods of preventing deposition on an optical component in an absorption spectroscopy measurement cell. The methods involve performing an absorption spectroscopy measurement of a sample gas introduced into the cell, and introducing a flow of purge gas from a purge gas inlet pipe across a critical surface of the optical element at a velocity effective to prevent deposition on the critical surface. The gas inlet is disposed adjacent said critical surface. Also provided are devices for practicing the inventive method, measurement cells useful in absorption spectroscopy measurements, apparatuses for performing an absorption spectroscopy measurement and semiconductor processing apparatuses. The invention allows for the performance of accurate spectroscopic measurements. Because deposits are prevented from forming on the surface of an optical element, interference therefrom can effectively be avoided.

Abstract: An exterior rear view mirror assembly for an automotive vehicle is provided including a bracket for attachment to a side portion of a vehicle, a mirror housing having a rear opening connected to the bracket and extending laterally therefrom, a mirror connected within the mirror housing generally adjacent the mirror housing rear opening, a water removal hole penetrating a bottom end of the mirror housing for allowing precipitation entrapped within the mirror housing to escape therefrom, a turbulent flow generator formed forwardly adjacent of the water removal hole to cause turbulent air flow past the removal hole to diminish wind noise being generated by the water removal hole.

Abstract: A wall-mounted cabinet having a pivotable door with opposed exterior and interior mirrors which can be convectively and radiatively heated to prevent fogging, by a sheet heater between the two mirrors. The exterior mirror is electrically insulated, and the exterior and interior mirrors are grounded to prevent electric shock.

Abstract: A self-cleaning, rotating mirror includes a compressor assembly mounted to a cylinder of a rotating mirror. As the cylinder and mirror rotate, the compressor assembly also rotates causing a continuous flow of clean air to be passed over the surface of the mirror, thereby preventing particles, such as dust, from depositing on the mirror surface.

Abstract: An optical element includes a first substrate having a diffractive surface or a surface structure with a surface level difference, a second substrate for covering the diffractive surface or the surface structure to provide a shield therefor, and a groove provided at the diffractive surface or the surface structure, and extending from a central portion to a peripheral portion thereof, for discharging or replacing a gas at the diffractive surface or the surface structure therethrough.

Abstract: The invention is directed to a film structure of a hydrophilic film in an anti-fog mirror of a type in which an inorganic oxide film is formed as a hydrophilic film on a surface of a mirror and to a method for manufacturing such film structure. A photocatalyzing TiO2 film having a thickness within a range from 100 nm to 1000 nm is formed on a surface of a mirror and a porous SiO2 film having a thickness within a range from 10 nm to 50 nm is formed on the TiO2 film. The porous SiO2 film is adapted to have surface roughness of 2 nm or over. A reflecting film is formed on a rear surface of a transparent glass substrate and then photocatalyzing TiO2 film and the porous SiO2 film are formed on a front surface of the substrate by vacuum deposition while the temperature of the substrate is maintained within a range from 200° C. to 450° C.

Abstract: An exposure apparatus in which exposure process is performed by projecting an exposure beam of X-rays or ultraviolet rays from an excimer laser, for example, to a substrate, is provided with an arrangement wherein an inert gas containing a small amount of oxygen is supplied to a closed space where an optical element is disposed, and wherein the exposure beam is projected thereto by which ozone is produced in the closed space. Organic compound deposited on the optical element can be removed by photochemical reaction through projection of the exposure beam and the produced ozone.

Abstract: A clearing system for external mirrors and side windows of a vehicle provides a flow of compressed warm air to an air distribution unit equipped with a number of openings to direct the flow of air towards the surface of the mirror or a side window. In one embodiment, the air compressor, the air heater and an optional air filter are located in the housing of the external mirror. In another embodiment, a supplemental air distribution unit is provided to be mounted along the door of the vehicle to increase the coverage area of the side window. In a further embodiment of the invention, the system is made adjustable for allowing the most appropriate angle for the air openings towards the mirror and the side window. Provisions are also made to use the system for newly designed vehicles and incorporate the elements of the system into the design of the vehicle door. Alternately, an add-on elements are described to allow existing vehicles to benefit from the system.

Abstract: A protective window assembly and its use with a focusing assembly lens in a laser beam generating apparatus, the protective window assembly contains a window with apertures for protecting the focusing lens against damaging and cooling the focusing lens.

Abstract: An exposure apparatus in which an exposure process is performed by projecting an exposure beam of X-rays or ultraviolet rays from an excimer laser, for example, to a substrate, is provided with an arrangement wherein an inert gas containing a small amount of oxygen is supplied to a closed space where an optical element is disposed, and wherein the exposure beam is projected thereto by which ozone is produced in the closed space. An organic compound deposited on the optical element can be removed by a photochemical reaction through projection of the exposure beam and the produced ozone.

Abstract: An optical assembly for mounting in a vehicle employs a two piece assembly including a bracket having a front surface and a back surface and an optical device having a front surface and a lens element on the front surface. The back surface of the bracket is connected to the vehicle and the front surface of the optical device is removably attached to the back surface of the bracket. The lens element focuses an image through a windshield of the vehicle. In one embodiment of the present invention, the optical device further comprises at least one notch member and a support extension member and the bracket includes an opening and further comprises at least one groove member. The at least one notch member is positioned to removably attach to the at least one groove member, and the support extension member is positioned to removably attach to the opening. In one embodiment, the assembly is mounted to the vehicle windshield so that a driver of said vehicle has an unobstructed view of a road.

Abstract: The invention relates to a method of keeping a measuring window of a measuring device clean, and to a measuring device. Gas is blown onto the surface of the measuring window (2) of the measuring device (1). Gas is guided onto the measuring window (2) by a nozzle (3) which is substantially on the same level with the measuring window (2).

Abstract: A laser scanning system suitable for annealing applications is described. The problem of keeping the window (through which the laser shines into the system) clean, even though the laser ejects a considerable amount of debris, has been solved by inserting a moveable shutter close to the window between it and the substrate. The center portion of the shutter is an insert of optical quality quartz that is just large enough to allow the laser beam to pass through unimpeded and undiverted. By moving the beam and the shutter in concert it is ensured that the beam always passes through the insert. Most of the debris ejected by the laser as a side effect of its operation is trapped on the shutter. Relatively little material ends up on the quartz insert but when sufficient has accumulated there, the insert can be replaced at much lower cost than replacing the window. By moving the beam back and forth together with movement of the substrate, the entire area of the film on the substrate may be scanned by the beam.

Abstract: An apparatus is provided including a semiconductor processing chamber enclosed by a plurality of walls. Also included is a source of process gas that is required for processing a wafer within the processing chamber. Mounted on one of the walls of the processing chamber is a window. An inlet is positioned adjacent to the window and remains in communication with the processing chamber. The inlet is further coupled to the source of process gas to channel the process gas into the processing chamber for both preventing the deposition of byproducts on the window and further processing the wafer within the processing chamber. In another embodiment, a source of light, an analysis mechanism, and an optical transmission medium are provided. Such optical transmission medium is coupled between the source of light and the analysis mechanism and is further aligned with the window for directing light into the processing chamber and analyzing the wafer within the processing chamber.

Abstract: In a waterdrop removing apparatus for a vehicle, a blower is attached to a part of high rigidity within a door body to reduce vibration and noise. Air discharged from the blower is guided to a door mirror by a nozzle to blow away waterdrops wetting a surface of the door mirror. The blower is attached to an attachment bracket which is fixed to a door hinge together with a front end wall of the door body interposed between the door hinge and the attachment bracket.

Abstract: An aerodynamic exterior rear view mirror for motor vehicles that has low drag as a result of prevention of laminar boundary layer separation on the mirror head and subsequent turbulent wake size reduction. The vehicle mirror comprises an aerodynamic exterior shell having a continuously smooth surface with inboard and outboard trailing edges. The surfaces of the shell preceding the trailing edges can be either parallel or closing relative to the free stream airflow. A boundary layer control device that consists of a trip strip is formed on the exterior surface of the mirror head just upstream of the transition or separation point where the laminar boundary layer flow would transition to turbulent boundary layer flow with delayed separation or to complete separation absent the boundary layer trip strip. The trip strip, when correctly sized and utilized, will assist the laminar boundary layer to transition to turbulent boundary layer flow which reenergizes the boundary layer.

Abstract: A laser scanning system suitable for annealing applications is described. The problem of keeping the window (through which the laser shines into the system) clean, even though the laser ejects a considerable amount of debris, has been solved by inserting a moveable shutter close to the window between it and the substrate. The center portion of the shutter is an insert of optical quality quartz that is just large enough to allow the laser beam to pass through unimpeded and undiverted. By moving the beam and the shutter in concert it is ensured that the beam always passes through the insert. Most of the debris ejected by the laser as a side effect of its operation is trapped on the shutter. Relatively little material ends up on the quartz insert but when sufficient has accumulated there, the insert can be replaced at much lower cost than replacing the window. By moving the beam back and forth together with movement of the substrate, the entire area of the film on the substrate may be scanned by the beam.

Abstract: A fog-free shower mirror assembly comprises a mirror body (16) and an arm (18) connecting the body to a showerhead pipe (12). The arm is connected to the pipe by a T-fitting (14) that diverts warm water from the pipe to the mirror body. The T-fitting also returns the water after it passes through a heat transfer tube (56) in the mirror body. The arm is flexible and contains two inner tubes (36 and 38) for supply and return of the water. The arm is connected to the mirror body by a swivel fitting (20). The mirror body contains a thermal transfer disc (58) positioned between the heat transfer tube and the back of the mirror. Heat from the water in the heat transfer tube is thereby transferred to the mirror to keep it above the condensation point so as to maintain it fog-free. An additional mirror (68) that also is heated by heat from the heat transfer tube may be provided on an opposite side of the mirror body, also in thermal contact with the transfer tube.

Abstract: A water droplet removing system for a vehicle provided with door mirror assemblies each having a door mirror base attached to a door body, and a mirror unit guides air discharged by a blower installed in a door body of the automobile to at least either the surface of a mirror included in the mirror unit or the outer surface of a side window to blow off water droplets wetting the surface of the mirror or the outer surface of the side window. The blower is installed in a dead space defined in front of a guide rail placed in the door body to guide the front edge of the side window for vertical movement in the door body so that the interference between the blower and parts arranged within the door body including the side window can be avoided.

Abstract: Apparatus for optical analysis of a sample, including an energy source, which generates a pulse of energy that is incident on the sample, causing the sample to emit radiation characteristic of the composition of the sample, and a detector assembly, which receives and analyzes the radiation emitted by the excited sample. An optical assembly conveys the emitted radiation from the sample to the detector assembly, the optical assembly including an optic proximal to the sample, on which optic the radiation is incident along a beam path thereof between the sample and the detector assembly. A moving mechanical element moves in synchronization with the pulse from the energy source so as to substantially prevent matter ejected from the sample responsive to the incident energy from accumulating on the optic.

Abstract: A multi-hood system for correcting individual lens distortions includes an air supply hood provided on an outer circumference of a lens; a plurality of air dividing partitions for dividing the air supply hood into a plurality of divided regions; and a plurality of air supply lines for individually supplying air of predetermined temperatures to the divided regions of the air supply hood.

Abstract: In a rear view mirror for a motor vehicle with a housing connected with an air source, traversed by air guide channels, and holding a mirror glass, with the outlets of the channels being arranged along the edge of the mirror glass to allow air to escape opposite to the direction of forward travel of the vehicle, modified guidance and processing of the escaping air reduces the danger of contamination of the mirror glass by the wind blast as well contamination of the side window associated with the mirror. This is also intended to improve the flow resistance of the mirror as well as its noise behavior. For this purpose, a plurality of separate air channel outlets is provided that are located within a guiding device and/or are equipped with one that produces vorticized air streams that emerge and are stable at each of the air outlets.

Abstract: A protective window assembly and its use with a focusing assembly lens in a laser beam generating apparatus, the protective window assembly contains a window to protect the focusing lens against contamination and the like.

Abstract: A photoelectric sensor has its own cleaning system which accommodates different possibilities for mounting the photoelectric sensor, so that it is no longer necessary to custom design cleaning systems. The photoelectric sensor includes an optical lens and a cleaning device which cleans the optical lens. The cleaning device further includes a fluid chamber coupled to a source of fluid, and a fluid dispenser in fluid communication with the fluid chamber and disposed adjacent the optical lens. The fluid dispenser is operative to dispense fluid on the optical lens to clean the optical lens. In a preferred embodiment, the cleaning system uses a pulse of air to remove dust from the optical lens of the photoelectric sensor.

Abstract: An anti-fog element includes a transparent substrate such as a glass substrate, a transparent film of a photocatalyzer such as TiO.sub.2 catalyzing a photocatalytic reaction on the transparent substrate, and a film of a transparent porous inorganic oxide such as SiO.sub.2 formed on the film of the photocatalyzer and having a surface exhibiting a hydrophilic property. Organic matters etc. deposited in openings of the porous inorganic oxide film are dissolved and removed by a photocatalytic reaction caused by light excitation of the photocatalyzer film whereby the anti-fog property of the anti-fog element can be maintained over a long period of time.

Abstract: A mirror assembly includes a mirror and a device for preventing said mirror from being steamed up by circulating hot water through a back side of the mirror, the hot water flowing along a hot water supply tube when using hot water in a bathroom. The device has a frame for supporting the mirror at the back side of the mirror and a pipe disposed in the frame, the pipe having inlet and outlet ports connected to downstream and upstream sides, respectively of the hot-water supply tube, respectively, so that part of the hot water can be introduced into the pipe and returned to the hot water supply tube after being circulated therein.

Abstract: An improve method and apparatus for removing beaded water from the reflective surface of a vehicle mirror is provided. The apparatus comprises a metal wind scoop assembly that is mounted to the mirror. The wind scoop assembly, together with the structure of the mirror, defines a windward facing intake scoop and an exhaust slot located adjacent the surface of the mirror. The inlet scoop intercepts an air stream created by movement of the vehicle and the stream is redirected and exhausted through the exhaust slot along the surface of the mirror. The exhausted stream blows beaded water from the mirror to clear and dry the mirror for better vision.

Abstract: A remotely adjustable rearview truck mirror includes a streamlined housing that is stationarily secured to the exterior of the truck cab, the housing having walls that define an enclosure that has a rearwarly facing rectangular aperture. A generally rectangular mirror support covers the aperture and is pivotally mounted for rotation about a vertical axis through one side of the aperture, and a sealing lid or flange extends generally forward from the periphery of the mirror support so as to lie in close overlapping relationship with the periphery of the aperture, and a sealing element extending along the aperture periphery, slidably engages the flange, and an electrically driven drive mechanism within the enclosure can be controlled from the cab to adjust the orientation of the mirror support. A wiper blade mechanism and a heater are mounted to the mirror support, and spray nozzles on the mirror support are supplied from a reservoir within the enclosure.

Abstract: A scanner for scanning a one or two-dimensional bar code symbology is provided that effectively prevents condensation from forming on the protective window. The scanner comprises a housing having an electro-optical element and a window permitting the electro-optical element to collect reflected light therethrough. A heating element is coupled to at least a peripheral portion of the inner surface of the window. Application of an electrical current to the heating element heats the window and precludes condensation from forming on the inner surface of the window. The heating element may further comprise a resistive element having an adhesive layer permitting attachment to the inner surface of the window. The heating element would be further compatible with operation of conventional electro-optical elements, such as a charge coupled device or a laser.

Abstract: A viewing system for a vehicle has a mirror body protruding from a side of a vehicle, a light collecting element collecting light coming from the a rear field of view of the vehicle, a reflection element for reflecting light collected by the light-collecting element to the inside of the vehicle toward a field of view of a driver, and a rotating unit for rotating the light-collecting element so as to repel water drops adhering to its surface.

Abstract: In an ultraviolet exposure apparatus, substances contained in an atmosphere contacting a lens surface are reduced, the substances generating accumulations on the lens surface. Openings are formed in the wall of a lens barrel to allow the atmosphere to be replaced by a proper gas. The proper atmospheric gas may be a gas not containing oxygen such as a nitrogen gas, or clean air obtained by intentionally generating accumulations by applying ultraviolet light to source air. A ultraviolet light source is preferably cooled by a cooling system different from the cooling system of a lens optical system.

Abstract: The mirror housing of the automobile sideview mirror is of an ordinary shell type and so formed at the lower edge of the front opening thereof as to have a generally V-shaped section of which the front arm of the letter "V" protrudes outwardly and is followed by a portion bent at the end of the front arm and extending almost horizontally and inwardly of the mirror housing.

Abstract: A condensation-free shower mirror includes a mirror (10) enclosed by a housing (12). The housing is attached to one end of a positionable arm (16), which has a C-clip (17) at another end for clipping onto a water pipe (18) of a shower head (19). The rear surface of the mirror has a protective coating or backing. Prior to shaving or other use, the mirror is positioned in a hot shower stream (20) to be heated. When the mirror is heated above the dew point of water, it will become free of condensation, and can be used for shaving or grooming, either with the hot water continuing to flow onto its rear surface, or after it is moved away from the water spray. After use, it can be easily positioned away from the shower stream so that the user can resume normal showering. The mirror can be easily detached from the pipe and easily clipped onto another, so that it can be used in different hotel rooms when traveling, as well as in the home.

Abstract: A purge assembly for mounting to a radiation thermometer, comprises a purge tube for mounting in front of the radiation thermometer. At least two axially spaced chambers are positioned about the purge tube, each pair of chambers being linked by a respective restrictive opening such that a difference in pressure exists between adjacent chambers in use. An upstream chamber with respect to the flow of purge fluid is connected to source of purge fluid such as air in use and a downstream chamber with respect to the flow of purge fluid opens into the purge tube via a swirl reducing system whereby purge fluid is emitted into the purge tube in use. The chambers are positioned such that fluid flows through the chambers generally towards the lens and then through the downstream chamber opening towards an outer end of the purge tube away from the lens.