Abstract: A microfiche reader is disclosed herein and includes an assembly for supporting a microfiche in a given area, a projection screen and an optical arrangement for providing an image of a segment of the microfiche on the screen. This arrangement utilizes a dual projection lens assembly and a dual condenser lens assembly which cooperate with one another so that the magnification of the projected image can be easily varied between two levels. As disclosed, the dual projection lens assembly itself includes two distinct projection lenses which are contained in collapsible housings. Moreover, each of these latter lenses is adjustably focused by rotational movement of its associated housing and remains in the focusing position selected unless its housing is again rotated.

Abstract: A filmstrip viewer/projector unit includes two separate projection lenses, one for front projection on a remote screen and the other for rear projection on a small local viewing screen built into the unit. A film carrier has two separate apertures therein respectively disposed in optical alignment with the two projection lenses for cooperation therewith to define first and second optical axes. A lamp directs a beam of light to a plane mirror disposed between the lamp and the film carrier and movable between two positions for respectively reflecting the beam of light along the first and second optical axes, respectively for projecting the film image onto the associated remote and local screens. First and second condenser lenses are respectively disposed along the optical paths between the reflector and the film carrier. The projection lenses share a common focusing mechanism.

Abstract: A portable microform viewer provides a short film path through a film transporter that adjustably positions the film in two directions by means of a pair of concentric knobs. A pair of projecting lenses is shiftably mounted for selection of one or the other and the two are mounted on a common pivoted focusing plate. Film is positioned within the film transport by means of a pair of glass flats that are detachably mounted in the transport and flexibly connected to each other for accommodation of microform of different thickness and for ready removal and complete cleaning.

Abstract: An electric motor which can drive the objective of a slide projector or which can adjust the blade or blades of a diaphragm receives signals from the output of an operational amplifier which receives first and second signals from a photosensitive transducer and a differentiating capacitor. The (second) signals from the capacitor are modified (first) signals from the transducer, and the combined intensity of first and second signals is such that the signals at the output of the amplifier reach a value which they would normally reach only when the component has already assumed a predetermined position before the motor can complete the movement of the component to such position.

Abstract: A microfilm reading device in which a lens carrier is provided with two projecting lenses which are in axial parallel alignment with each other. Through actuating a handle which is disposed between the projecting lenses, the projecting lenses can be moved from a first position in which the lens is brought in alignment with a micrograph to be projected into a second position in which the lens is lifted while the other lens is brought in alignment with the micrograph.

Abstract: An image focusing apparatus for microfiche film readers and other optical systems has a lens holding apparatus which rests on a transparent or glass plate, a rotatable lens adjusting assembly in the lens holding apparatus, a shaft slidably and pivotally connected to the lens adjusting assembly, a knob on the shaft, and a shaft holder which fixes the position of the shaft with respect to the reader. The lens holding apparatus is universally mounted to the frame of the reader to enable the lens holding apparatus to move freely in response to changes in the angular disposition of the glass plate with respect to the horizontal plane. The lens adjusting assembly has an eccentric finger which translates the rotating motion of the knob and shaft into a vertical force, which moves the lens. The lens adjusting assembly has a barrel, a socket in the barrel and key slots along the socket. The shaft has a partially-spherical end and keys which slidably and pivotally fit into the socket and key slots.

Abstract: A lens nesting member carries a plurality of lenses in position to enable rapid selection of a desired lens and photoelectric means is provided for sensing and for identifying the desired lens.

Abstract: A microfilm reader for enlarged projections of any desired micropicture among a number of such pictures on a microfilm. The microfilm is interleaved between two movable plates. A slidable support for the image forming objective is pressed with a tensioned spring against the upper plate. The slidable support can be connected to a slide lever for effecting its placement in proper position. Two arms of a spring can be employed for mounting the slidable support and for tilting it around an axis essentially parallel to the cover plate.

Abstract: A slide projector located within a rear-screen projector has means therein for projecting images, contained on slides, onto a self-contained projection screen. Two lenses having different focal lengths are mounted within the projector housing and may alternatively be brought into the optical path for projecting slides, having different size formats, such that the projected image fills the projection screen.

Abstract: An objective lens supporting arrangement for microfilm reader. The objective lens is axially movable and at the same time non-rotatably mounted with respect to a holding tube of the arrangement. An adjusting ring is coaxially mounted with respect to the holding tube and rotatable relative thereto. An angular displacement of the adjusting ring relative to the holding tube effects via cam means an axial adjustment of the objective lens for the purpose of focusing it.

Abstract: A method and apparatus for detecting the focusing condition of an optical system is disclosed. Different portions of the optical system are alternatively obstructed to form first and second or more images, respectively, of an object. When the optical system is in focus, the aforesaid first and second images coincide and present a single image. When the optical system is out of focus, the first and second images are displaced with respect to one another. Alternately obstructing different portions of the optical system gives the appearance of a moving image when the first and second images are displaced in response to the optical system being out of focus. Alternately obstructing different portions of the optical system gives the appearance of a stationary image when the first and second images coincide in response to the optical system being in focus. Thus the presence of either a stationary or moving image is an indication of the focus condition of the optical system.

Abstract: The present invention provides a system for automatically focusing a projected film image by maintaining a predetermined distance along the optical axis between the emulsion on the surface of the film and the projection lens. The system includes a movable carriage for mounting the projection lens and an electro-optic sensor mounted for movement with the carriage for maintaining the predetermined distance. The electro-optic scanner includes a light source and lens assembly for focusing a beam of light onto the surface of the film and a lens for focusing the reflected image onto a dual phototransistor receptor. A servo-amplifier is connected to the output of the dual phototransistor to provide appropriate signals to the carriage drive mechanism to maintain said predetermined distance. The servo-amplifier utilizes both positional and rate feedback to provide faster operation and settling.

Abstract: Slide projectors with automatic focusing systems consisting of a scanning auxiliary projecting system and a position control focusing the slide and comprising a light sensor detecting the reflections from the slide are improved by mounting the light sensor outside the scattered light zone generated when the main projection beam passes through the slide. The light source of the auxiliary projecting system is operated at less than rated voltage and silicon cells are used as light detectors. The light course comprises a lens which is mounted in the same manner as the light sensor on holders and the holders are pivotably supported for the purpose of adjustments.

Abstract: A projector for motion pictures or slides has a varifocal objective with a positive front component, an axially slidable negative intermediate component and a fixed positive rear lens group. The front component, or at least its foremost lens member, has a lens mount which is displaceable along a track substantially transverse to the optical axis; the track may be curved with its convex side facing the projection screen. A diaphragm just behind the front component has an aperture barely exceeding the diameter of the intermediate component whereas the front component (or its transversely displaceable part) is radially extended past the diaphragm aperture so as to register with it in every position.

Abstract: An electronically controlled photographic image utilization device is arranged to transport a roll of microfilm having all images printed thereon in separate photographic areas, each area being arranged in a microfiche-type format. The photographic image utilization device has an automatic call-up feature so that any given photographic area may be selected in a first dimension and projected responsive to the push of a button, the operation of a rotary switch or both. A special bar code is printed along the edge of the film and used in conjunction with a closed loop film control system to eliminate the need for precise, clock-controlled synchronization between the film transport and the code reading. Preferably, the bar code is read by optical electronic sensors. Responsive thereto, the electronic control system accurately positions a selected photographic image, on the microfilm, within a viewing area.

Abstract: This invention discloses an automatic focusing device for cameras and other optical apparatus which comprises scanning means for at least a portion of the focused image, and the scanning current varies the focusing means automatically until the scanning current shows a maximum of high-frequency component to low-frequency component power.

Abstract: A microfiche reader according to the present invention includes a housing consisting of a hood portion and a base portion, a screen located within the hood portion and visible through the front end of the hood, a combined microfiche carriage and index holder, a lens assembly and a projection system. The combined microfiche carriage and index holder serves to accurately locate the microfiche with respect to the index grid. By reason of the fact that there is no relative movement between the index grid and the microfiche in use, it is always possible to accurately locate the microfiche with respect to the projection system by reference to the index grid. The index grid is illuminated by an index illuminating lens carried by the housing. The illuminating lens is located in a fixed relationship with respect to the projection path which again contributes to the facility with which the microfiche may be accurately located in the projection path.

Abstract: A remotely controlled projection zoom lens apparatus utilizes a zoom lens assembly having a spur gear fitted to the barrel element of a zoom lens rotationally driving a zoom lens element. Another spur gear is co-axially aligned with an iris element operable in line with the zoom lens assembly. Both spur gears are in turn operated by a gear train and powered by a common motor. A slip clutch may be interposed between the motor output shaft and the gear train or between the gear train and either or both spur gears, permitting the iris barrel or zoom barrel to engage stop position without damage when one or the other is driven to a stop position by the motor, or to adjust angular position relative to one another. The gear train is rotationally coupled to a potentiometer, which in turn signals the position thereof to a remotely located indicating device. The motor is controlled from the remote location as well.

Abstract: A magnification of the displayed image of an opaque reader can be changed between first and second values by a single manual movement. A diopter lens disposed in front of the projection lens provides a first magnification. The single movement functions to remove the diopter lens and simultaneously shift axially the position of the projection lens thereby providing the desired second magnification, the simultaneous movement of the diopter and projection lens from first to second positions assuring that the magnified images under both magnifications are in focus.

Abstract: The inventive microfilm reader and reader-printer has a film gate which is anchored to the chassis of the reader or reader-printer and which is entirely separate from a light system, lens mount, and focusing system which float up and down with respect to the film gate and chassis. The floating system is mounted on an elevator mechanism which lifts or lowers it relative to the film gate to scan across the width of the film. A prism is included in the lens system to rotate and vertically align the projected image. A combination of the movements of the elevator mechanism and prism enables any vertical segment of the microfilm to be scanned, selected, and read in a vertical orientation.

Abstract: A microfiche viewer structured for examining new microfiche film. The film is typically still in roll form as it comes from the microfiche camera. Plural magnifications of the microfiche image are selectively available; one, to reproduce a whole fiche upon the viewing screen for general observation of photographic quality, the other, to reproduce perhaps four frames of a whole microfiche for detailed observation of quality. The apparatus is structured for convenience in viewing. The different magnifications are obtained by selectively interposing objective lenses of different focal length in the light path adjacent to the microfiche film on the side opposite to that occupied by a light source. Motor driven film transport means are provided atop the apparatus proper.

Abstract: A microfiche reader providing varying optical paths of projection of a microfiche image. The light source for the reader may be removed and readily replaced without the operator's touching the sensitive lamp. Dual image forming, floating lenses having a universal focusing system provide multiple magnification capabilities with uniform focusing in all positions of the microfiche. The focusing system is self-compensating for mechanical tolerances. Additional means prevent chipping of the glass plates holding the microfiche when the floating lenses are removed from contact with the glass plates.

Abstract: A microfiche reader providing varying optical paths of projection of a microfiche image. Variable hood means provide self-contained viewing, or projection of the image on a screen, wall or ceiling. The light source for the reader may be removed and readily replaced without the operator touching the sensitive lamp. Dual image forming floating lenses having a universal focusing system provide multiple magnification capabilities with uniform focusing in all positions of the microfiche. Additional means prevent chipping of the glass plates holding the microfiche when the floating lenses are removed from contact with the glass plates.

Abstract: A projection device provided with at least two different enlarging projection systems for the projection on a screen of a set of at least two slides provided on one carrier, said slides covering the same area of a plan or map, one slide being more detailed than the other. The device projects the first less detailed slide entirely and the second or next, more detailed slide only in part but on a larger scale.The device comprises further a transparent runner indicating on the first slide the part of the next slide that is projected.

Abstract: An apparatus for displaying a magnified image having a console with a rear lighted projection screen, the console including a light source, a specimen holder, and a lens system for displaying a magnified image of the specimen on the rear surface of the screen, the console being arranged such that the screen is mounted for easy view by the user, the improvement including a magnifying glass supported by the console in front of the screen and variable in spacing with the screen for focusing by the user, the magnifying glass being movable over at least a significant portion of the screen so that the user can obtain a magnified view of selectable portions of the screen through the magnifying glass.

Abstract: A slide projector for use with magazines of the flexible type in which slides are supported for movement around a closed-loop path and are swingable one by one into and out of a slide-projection station about an axis defined by a rotary drive shaft. The magazine has individual clip-type slide-holding elements that slide along an endless path and have frames in which slides are held. A condensing lens is mounted and guided for movement from a normal operating position close to the slide-projection station and in the path of the slides, to a retracted position out of the path, with a combined reciprocating and swinging motion, and is moved back and forth by a rotary crank mechanism that is driven by the slide-feeding mechanism, to shift the lens rapidly out of and back into the operating position during each slide change, with a dwell in the retracted position for the change.

Abstract: Projector elements for a film projector selectively project an image onto a local viewing screen mounted on the projector housing or to a viewing screen remotely located from the projector. A projector mounted control is coupled to a reflecting mirror pivotable about a vertical axis and to position shiftable objective and condensing lenses to permit convenient single control shifting of the mirror and the lenses for either local screen viewing or remote screen viewing.

Abstract: An audio-visual phonograph device including a visual image projection system is provided which includes a case for the phonograph device having a lid that serves as a screen for the projection of images formed on a flat disc. The phonograph device further includes a variable speed turntable and a pick-up tone arm employed to reproduce the audio message on the records. The turntable is synchronized with a carrier onto which the visual image disc is removably mounted. The carrier rotates in synchronism with the turntable advancing a continuous image that is projected onto the screen in a timed relation with the correlated audio message.

Abstract: A semi-automatic coarse-fine focusing apparatus for microscopes adjusts the focus of a microscope through rotation of a shaft which rotates a pinion that drives a rack to reciprocate. The rack carries a specimen being observed by the microscope. The shaft which rotates the pinion is in turn driven by a gear that is meshed with a helix formed on a cylinder by a helical thread disposed therearound. The helix is non-rotatably mounted on another shaft that includes a knob which is manually turned to turn the helix and thus rotate the gear for coarse adjustment. The helix is preferably rigidly mounted on the shaft and the shaft is slidable. One arm of a bell crank engages an end face of the helix to reciprocate the helix and thus rotate the gear for fine adjustment. The other arm of the bell crank is engaged by a cam which pivots the bell crank according to the position of the cam. The position of the cam is determined by an electric motor which is preferably controlled by signals that vary with image contrast.

Abstract: An optical device for a micro-image viewer or a micro-image viewer-printer machine receives a projected image of an illuminated micro-image, adjusts the spatial disposition of the projected image in an image plane and transmits the adjusted projected image to a viewing screen for viewing or to an exposure station for reproduction purposes. The optical device, in a preferred embodiment, includes a pechan prism positioned in a micro-image viewer-printer machine for receiving a projected image from a projection lens assembly. The pechan prism is rotatable about the illumination path or optical axis of the viewer-printer machine to enable the spatial disposition of the projected image to be rotated at least from 0 degrees to 180 degrees in an image plane.

Abstract: Apparatus for focusing a lens or lenses in which the focus adjustment is stable and in which backlash is reduced to an imperceptible level without the use of precision components. A unitary lens carrier is mounted on a shaft for axial displacement thereon and includes a first section spaced from a second section. A rotatable cam is mounted between the two sections and a spring is disposed between the cam and the second section to urge the cam against a surface portion of the first section. Rotation of the cam causes axial displacement of the lens carrier.

Abstract: A microfiche reader provided with a pair of lenses of different powers selectively and simultaneously shiftable into and out of alignment with the fiche projecting light beam. The lens in use rests by gravity on an X-Y fiche transport supported on a turn table. The lens shifting mechanism includes a device holding the lens in use firmly stationary despite both rotary and linear movement of the fiche transport. Simple linear movement of the lens shifting mechanism functions to elevate one lens while lowering the other gradually into contact with the fiche transport. The lens support assembly includes components for automatically adjusting the intensity of the light beam to provide the same lighting intensity on the image viewing surface for each lens. The lens support assembly is readily removable as a unit for servicing and the substitution of another assembly while the first is undergoing repair.

Abstract: The disclosure relates to a microform reader apparatus of the type which projects a magnified image of an image film frame onto the rear side of a viewing screen to facilitate forward viewing of the magnified image. The microform reader of the present invention includes an adjustable mirror assembly positioned between a light source and condensing lens for optimizing the brightness of the displayed image. In a preferred form the mirror assembly is adjustable from the front of the microform reader to allow simultaneous monitoring of the brightness of the display while the adjustment is being made. The microform reader of the present invention also includes an adjustable lens assembly which allows the optical axis of the lens assembly to be adjusted for perpendicularity to the image frame surface.

Abstract: Disclosed is a slide projection apparatus convertible for projection of an image either onto a remote surface or onto a screen built into the housing of the apparatus. A door, for selectively blocking the projection path, is coupled with a projection lens supported on a carrier. The lens is alternatively positionable along a substantially horizontal axis for straight ahead external projection and is positionable substantially perpendicular to that axis for internal projection onto the built-in screen. During external projection, the lens is focusable. Upon return to internal projection condition, the lens is automatically focused for the built-in screen. The projection apparatus includes a device to cause the light source to be energized at a high brightness level for external projection and to be automatically changed to a lower brightness level for internal projection.

Abstract: A picture slide projector having provision for automatic focusing (i.e., provision for automatically keeping the projection lens and the picture slide at a constant distance from each other notwithstanding a buckling displacement of the slide under the influence of heat) is provided with means for moving the projection lens axially relative to the picture slide, to an out-of-focus position to produce a fading or dissolving effect on the viewing screen, while the slide is being withdrawn from the slide holder or gate and replaced by another slide. At the same time, the automatic focusing mechanism is rendered inoperative. Preferably also at the same time, the projection lamp is dimmed. When the slide changing operation is completed, the automatic focusing mechanism is rendered operative, and it serves to bring the projection lens back axially to the sharp focus position, the projection lamp being simultaneously brightened.

Abstract: The present invention is directed to a transparency projector, such as a slide or motion picture projector including a compact focusing mechanism having an objective lens carried within a lens barrel supported within a sleeve which is carried within the projector housing for axial reciprocal displacement along the optical axis. The sleeve is provided with means for engaging a guide rod supported within the projector housing for limiting movement of the sleeve to axial movement. A reversible electric motor is supported on the sleeve for movement therewith and is energized in response to slide position error signals received from an automatic focusing system of the type well known in the art. The electric motor operates to drive a disc rotatably carried on the sleeve. The disc is provided with a spiral groove on one face.

Abstract: A light focus sensor having first and second grids comprised of interlaced light transmissive and light reflective portions and a rotating optical modulator comprised of a plurality of alternate light transparent and light opaque portions. The modulator portions are half the size of the reflective portions of the grids and the modulator is positioned in relation to the grids such that the phase relationship between the portions of one grid and the portions of the modulator is 180.degree. different than the phase relationship between the portions of the other grid and the portions of the modulator such that the composite signal passing through the modulator is indicative of the directional movement required to achieve focus.

Abstract: The projector for slides comprising a lens system having clips to hold slides; magazine tensioning means; a magazine indexing and slide positioning assembly comprising pivotally movable slide positioning means having an operative position where a slide is held transverse to the projection axis of the lens system and an inoperative position permitting the indexing of the magazine and including shutter means movable in timed relationship with the magazine to prevent projection during the indexing of the magazine; and a lens unit focusing system including relatively movable platforms which are selectively manually and/or power operable and linearly slideable lens unit support means operatively connected to the said platforms.

Abstract: An optical device for a micro-image viewer or a micro-image viewer-printer machine receives a projected image of an illuminated micro-image, adjusts the spatial disposition of the projected image in an image plane and transmits the adjusted projected image to a viewing screen for viewing or to an exposure station for reproduction purposes. The optical device, in a preferred embodiment, includes a pechan prism positioned in a micro-image viewer-printer machine for receiving a projected image from a projection lens assembly. The pechan prism is rotatable about the illumination path or optical axis of the viewer-printer machine to enable the spatial disposition of the projected image to be rotated at least from 0.degree. to 180.degree. in an image plane.

Abstract: A bridge circuit which includes a photoelectric transducer furnishes input signals to a differential amplifier whose analog output signal varies in correspondence to the bridge unbalance. A first and second bistable threshold circuit changes the analog output signal into digital signals signifying bridge unbalance in a first direction, balance, and unbalance in the opposite direction. A motor is energized to rotate in a direction corresponding to the direction of bridge unbalance. The motor can be utilized to move the objective lens of a slide projector or change the aperture of a diaphragm.

Abstract: In a system which automatically analyzes laboratory slides, the adjustable objective lens is automatically focused. A beam splitter splits light from the slide into two parts. One slide image is projected to an actual image plane where it is converted into electrical signals representing the optical characteristics of the slide. The other slide image is projected to a parfocal image plane at which two light sensing devices for the focusing system are positioned. One light sensing device is in front of the parfocal image plane and the other is behind the parfocal image plane. These light sensing devices produce electrical signals representing the position of the actual image plane with respect to the desired image plane. The electric signals are differentiated and then applied to a comparator which supplies pulses to a stepping motor which moves the objective lens.

Abstract: Means to manually or power focus the adjustable lens unit of the projector. The power adjustment can be made irrespective of the position of the adjustable lens unit and safety features are incorporated which prevent locking and possible damage to the adjustment means when the limit of adjustment of the lens unit in a given direction has been reached.

Abstract: In order to compensate for the "Keystone-effect," a still projector is equipped with a vertically adjustable lens holder, which is coupled by a sliding pivot to a pivotable lamp housing. The lamp housing has a pair of arms projecting therefrom, which have slots extending therein which, in turn, register with pins positioned in the lens holder. The pins are located adjacent the rear nodal plane of the lens, and are aligned with an axis, which intersects the optical axis of the lens. Upon adjusting the holder vertically, the lamp housing will tilt to insure that the projected image will angularly conform to the original.

Abstract: Disclosed is a device for automatically focusing optical images wherein a rotating transparent disk having at least two sections of different focus delay characteristics is operative to pass a portion of an image carrying beam therethrough and onto a photoconductor. Output signals from the photoconductor are indicative of the degree of image clarity of the light incident thereto and these signals are passed to signal detector circuits wherein the signal resulting from light passing through the first section of the disk are compared with those signals resulting from light passing through the second section. The comparison of these signals is indicative of the degree of focus of the light beam and an error signal corresponding thereto is created from the outputs of the signal detector circuit.

Abstract: A film projection viewing system employs a projector to receive cartridges loaded into the projector in a manner completing a light path through the projector to a viewing screen. A film projector and cartridge having a substantially self-contained film transport therein cooperates to provide a system having a lens system with a focal length setable to a predetermined position in response to insertion of a cartridge into the projector.

Abstract: Apparatus for retrieving images of microfilms on sheet-like microforms on which the microfilms form frames arranged in vertical and horizontal rows and including larger and smaller frames. A transporting unit can move a microform up or down in a vertical plane so as to place a selected horizontal row of frames in front of a horizontal light source. A carriage in front of the transporting unit supports two lenses which are in line with the light source and respectively serve to project the images of larger and smaller frames onto the screen of a television camera. The carriage is movable horizontally to place a selected lens into register with a selected frame of that horizontal row of frames which is located in front of the light source, and the carriage can transmit motion to a plate- or belt-like diaphragm which is disposed between the transporting unit and the lenses and has one or more apertures registering with that lens which projects the image of a selected frame onto the screen.

Abstract: An optical system for projecting an image of an object, operating between fixed object and image planes. Both the object conjugate and the image conjugate are variable to vary the magnification in the system. This is accomplished without moving the optical axis by means of a first roof mirror on the object side of the lens and a second roof mirror on the image side of the lens. These mirrors each fold the optical axis by 90.degree. and are movable along a locus at 45.degree. to the optical axis to change the object and image distances.

Abstract: A system for automatically focusing images of different magnifications to be reproduced onto a light sensitive medium. First and second optical patterns of a wavelength to which the light sensitive medium is not responsive are projected from first and second displaced light pattern producing means to the projection plane of the images to be reproduced and back to the light pattern producing means. The light pattern producing means have transparent portions therein such that when the returned optical patterns are defocused portions of the defocused optical patterns are transmitted through the transparent portions. The transmitted light is then mechanically modulated and then converted to an electrical signal which is amplified, filtered and then demodulated to provide a signal having the polarity needed to drive a servo system such that focus of the images to be reproduced is achieved.

Abstract: A distance detecting device utilizable in an optical device such as a camera and the like requiring focusing operation of the optical system thereof. The detecting device enables the adjustment of the relative optical length between the group of light receiving elements arranged adjacent to the image forming plane of the object to be measured by the distance measuring optical system and the distance measuring optical system. The detecting device is characterized in that the output of each of the light receiving elements of the groups is introduced through an electric switching device for effecting the time seriation of the outputs of the respective light receiving elements into a common signal processing circuit, so as to adjust the relative optical length by means of a motor provided in responsive relationship to the output of the signal processing circuit thereby permitting the focusing of the image on the groups of the light receiving elements to be made to the most proper condition.