Lamp housing for use in photographic enlargers or the like
United States Patent Turner 1 1 Apr. 1, 1975 [54] LAMP HQUSING FOR USE IN 3.669.533 6/1972 Fowler i 355/67 PH G ENLARGERS OR THE 3.684.371 8/1972 Wcisglass t t 1 1 1 355/71 3.8311121 8/1974 Mcchloggcr 355 7] X LIKE Inventor: James Turner, Harrow. England Agta-Gevaert Aktiengesellschaft. Leverkusen. Germany Aug. 1, 1973 Assignee:  
 Filed:  
 App]. No.:  
 Foreign Application Priority Data Aug, 8. 1972 Germany .1 2238944 References Cited UNITED STATES PATENTS 2/1914 Leeds 355/71 5/1916 Boyd ct a1 240/4451 12/1964 Dccrst ct a1. 355/71 Primary lirmniner-Samuel 5. Matthews Al&#39;s/smut Etuminer-E. M. OConnor Attorney. Agent, or FirmMichael S. Striker I57] ABSTRACT A convertible light confining device for use in lamp housings of photographic projection printers resembles a hollow truncated pyramid through which the light passes in a direction from the top plane toward the base plate or vice versa, The sides of the truncated pyramid have rectangular or trapezoidal central portions which are pivotable inwardly about axes located in the top plane to form a second light duct of constant cross-sectional area or a second light duct which resembles a hollow truncated pyramid having a base plane coinciding with the top plane of the first truncated pyramid and a top plane which is smaller than but coplanar with the base plate of the first pyramid.  
 16 Claims, 5 Drawing Figures LAMP HOUSING FOR USF IN PHOTOGRAPIIIC ENLARGERS OR THE LIKE BACKGROUND OF THE INVENTION The present invention relates to light confining devices in general. and more particularly to improvements in light ducts or light pipes which can he used in lamp housings of photographic projection printers or the like.  
  In a photographic projection printer which is used as an enlarger. the image of an original must be projected onto a layer of photosensitive material to make a print. A versatile enlarger should be capable of making enlargements of different sizes. ie. to make larger or smaller prints from a negative. In presently known enlargers. the light is not utilized with a satisfactory degree of economy. This is due to the fact that. in such enlargers. only the area of the largest negative is illuminated uniformly and with a maximum degree of efficiency; however. if an enlargement is to be made from a smaller negative. the superfluous illuminated area is covered with opaque masks which results in considerable losses of light energy and prolongs (relatively speaking) the projection time. It is also known to use in such projection printers sets of interchangeable condensor lenses or to furnish the printer with interchange able light duets. Interchangeable lenses or ducts reduce light losses but their mounting in or removal from the projection printer takes up much time with attendant losses in output.  
 SUMMARY OF THE INVENTION An object of the invention is to provide a photographic projection printer with a novel and improved light confining device which can be used in the lamp housing as a light duct and can be converted to properly illuminate larger or smaller areas of photosensitive material with minimal losses in time and without necessitating even partial dismantling of the lamp housing.  
  Another object of the invention is to provide a convertible light confining device which can be used for making enlargements from originals of different sizes and is sufficiently simple to be entrustahle to semiskilled or unskilled persons.  
  A further object of the invention is to provide a convertible light confining device which can be installed in existing projection printers as a superior substitute for presently employed sets of light ducts.  
  An additional object of the invention is to provide a convertible light confining device which does not occupy more space than a conventional light duct.  
  The invention is embodied in a lamp housing for use in photographic projection printers or the like. and more particularly in a light confining and guiding device which forms part of the lamp housing and comprises a plurality of walls movable between first and second positions. When the walls are moved to the first positions. the light confining device constitutes a first light duct in the form of a hollow truncated pyramid with spaced apart top and base planes and sides which confine light that enters the first duct by passing across one of the planes and issues from the first duct by passing across the other plane. When the walls are moved to the second positions. the light confining device eonstitutes a second light duct which may form a second hollow truncated pyramid or a hollow shaft of constant or nearly constant cross section from end to end.  
  In accordance with a presently preferred embodiment. the walls constitute the central portions of the sides ofthe first light duct and are pivotable about a\e located in the top plane of the first duct. One of the light ducts is preferably located within the confines of the other light duct.  
  The novel features which are considered as characteristic ofthe invention are set forth in particular in the appended claims. The iniprmed lamp housing itself. however. both as to its construction and its mode of op eration. together with additional features and advantages thereof. will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing BRIEF DESCRIPTION OF THF. DRAWING FIG. I is a fragmentary schematic elevational view of a photographic projection printer having a lamp hous&#39; ing with a light duct which embodies the invention:  
  FIG. 2 is a diagrammatic perspective view of a light duct which is constructed and assembled in accordance with a first embodiment of the invention;  
 FIG 3 is a perspective view of a modified light duct;  
  FIG. 4 is a fragmentary vertical sectional view of the light duct shown in FIG. 3&#39;. and  
  FIG. 5 is a fragmentary vertical sectional view of the light duct shown in FIG. 2.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I. there is shown a portion of a photographic projection color printer which is used as an enlarger and embodies a lamp housing including the improved convertible light confining and guiding device. The light issuing from a source I is reflected by a reflector 2 so that it passes through a light confining device 4. The top part of the device 4 is adjacent to a unit 3 which includes a diffusing screen. means for changing the color of light and a shutter. The lower end of the device 4 is adjacent to a further diffusing screen 5. The parts 2-5 together constitute a lamp housing for the light source I. The light issuing from the device 4 and passing through the diffusing screen 5 thereupon passes through an original 6 and is focussed by an objective lens system 7 so that a portion 6a ofthe original is imaged onto a section 811 of photosensitive print material 8. The lens system 7 preferably includes a lens of variable focal length. Save for the improved device 4. the just described enlarger is of conventional design and is of the type which is used extensively for automatic making of prints from originals. cg. from sticcessivc frames of an exposed and developed photographic roll film. Enlargers employing light ducts in place of conventional eondensor lenses are preferred for the making of color prints because the light duct serves as a means for mixing the colors of printing light in accordance with the setting of the color changing means (such as filters) forming part of the unit 3. The means for transporting the originals 6 and the photosensitive material 8. the control means for the unit 3 and other conventional parts of the enlarger are not shown in FIG. I.  
  The construction of the improved light confining device 4 is shown schematically in FIG. 2. The diffusing screen 5 and the unit 3 are omitted in FIG. 2 for the sake of clarity. Basically. the light confining device 4 comprises a light duct in the form of a hollow truncated pyramid which. in the emhodiment of HG. 2. is a regular quadrangular truncated pyramid with a hase plane 42. a top plane 40 which is assumed to he parallel to the hase plane 42. and four trape/oidal sides. I he light en ters h passing across the top plane 40 and issues hy passing across the hase plane 42 which latter is o\crlapped hy the diffusing screen 5.  
  In accordance with a feature of the invention. each ofthe four trapc/oidal sides comprises a pi\otahle trape/oidal central portion or wall 4|. 4lli. 41:. 41d and two triangular corner portions 420&#39; a&#39;.4Z/1*42/ 42 421 421L421. When the central portions or walls &#34;IH llf are pivoted from register with the respective corner portions. they constitute a second light duet in the form of a second hollow truncated pyramid having a hase plane coinciding with the top plane 40 of the light duct with the hase plane 42 and four sides t-Ha-4Idl. The top plane 4] of the smaller second truncated pyramid is coplanar with or adjacent to the hasc plane 42. The edge portions 40a. 40b. 40v. 401/ define pi\ot a\es which are located in the plane 40 and ahout which the walls 4lu 4lrl are pivotahle from alignment with the respectne corner portions to the positions shown hy solid lilies in which they constitute the sides ofthc smaller truncated pyramid. Thus. hy the simple e\pedient of pivoting the walls 4lu 4lrl ahout the edges Miro-40d. one can convert the relatively large light duct with a hase plane 42 into a relatively small light duet with a hase plane 40.  
  The details of means for moving slightly modified central portions or walls 4lu&#39; 4lrf&#39; hetween the solidline second positions and the first positions of alignment with the respective corner portions 42u42u&#39;. 42IP4Z/i&#39;. 421 120. 4211-4211&#34; are illustrated in FIGS. 3 and 4. The walls -Hu&#39;4ltl&#39; are rectangular so that they may constitute a parallelpiped second light duct with a base plane 40&#39; which is of the same she as the top plane 4!. The walls 4lu&#39;4ld&#39; are respectively hiased hy helical springs 43a. 43b. 43. 43] which tend to maintain them in alignment with the respective corner portions whereby the walls form part ofthe sides of a truncated pyramid having a hase plane 42&#39; and a top plane 40&#39;. Each helical spring is attached to that part of the respective wall which is remote from the corresponding edge portion 40a, 40b. 40:. 4th! and the springs are further secured to fixed retainers 44a. 44b, 44; 44:! on the rigid frame of the enlarger. The frame is further rigid with the corner portions 42u-421l&#39;. The walls 41a. 4H). 41&#34;. 41d are further provided with arcuatc followers 45a. 45/ 451&#39;. 451/ which are adjacent to the respective edge portions 4(lu&#39;4lld&#39; and ahut against the underside of a ring-shaped actuating inertiher 46 which is movahle in and counter to the direction indicated hy an arrow 47. When the actuating member 46 is moved upwardly. as viewed in FIG. 3. the springs 43u-43u&#39; are free to contract and to return the walls 4lu&#39;--H I&#39; to their first or outer end positions.  
  As shown in FIG. 4. the wall 4k&#34; is substantially vertical when it forms one side of the smaller light duct and makes an oblique angle with the hasc plane 42&#39; when it forms part of one side ofthe larger duct. There* fore. the larger duct must he provided with additional portions or sills 4811. 48/). 48c. 48d which are respectively aligned with and are adjacent to the lower edges of the walls 4lu&#39; 4ld&#39; when the walls form part of the larger duct. Such sills are desirahle whenever the angle heta hetween the hase plane 42&#39; aitd a wall 4hr. 4H1. 4h&#34; or 4k! in the inner end position of such wall is larger than the angle alpha hetween the hase plane 42&#39; and a wall in the outer end position of such wall Referring to l&#34;l(i. 5. there is shown a wall 411! which is assumed to form part of the light confining device of FIG. 2. The angle alpha equals the angle heta and. therefore. the sills 4811-4811 of FIG. 3 can he dispensed with. However. and in order to avoid that the wall 4hr estend downwardly and heyond the hase plane 42 (ie. that the wall 41:: need not move the diffusing screen 5 of FIG. I downwardly) while the wall 4Iu pivots he tween its two end positions. the wall 4h! is coupled to the retttaining parts of the light confining device 4 hy a pin-and slot connection 40m! to thus insure that the wall can move up or down during pivotal movement hetween the positions shown in Fl(i, 5.  
  The length of a side of the smaller duct should not exceed the length of a side of the larger duct hecause. otherwise. sills must he provided in the larger duct to he aligned with the pivotahle walls in the inner end positions of the walls. Such sills would interfere with the travel of light through the larger duct. Therefore. the angle alpha is smaller than or at most equals the angle heta, i.c.. the inclination ofthe sides of the smaller duct relative to the hase plane of the larger duct should not exceed the inclination of the sides of the larger duct.  
  It is to he noted that the light confining devices are normally longer than those shown in FIGS. 2 and 3. The ratio ofthe maximum transverse dimensions to the height or length of a light confining device depends on the characteristics of the light source I. on the characteristics of the reflector means 2. and/or on the type of the unit 3. The inner sides of the ducts are coated with light reflecting material.  
  The improved convertible light confining device can he used in automatic copying apparatus as well as in many other optical apparatus. such as projectors. viewers or light hoses serving to illuminate differently di mensioned slides. frames or motion picture film or the like. This renders it possihle to operate a projector without necessitating a replacement oi interchange of condensor lenses.  
  The hasc and top planes of the smaller and larger ducts need not he rectangles or squares. Thus. the im proved light confining device may have any desired polygonal crosssectional outline.  
  Without further analysis. the foregoing will so fully reveal the gist of the present invention that others can. hy applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contrihuation to the art and. therefore, such adaptations should and are intended to he comprehended within the meaning and range of equivalence of the claims.  
  What is claimed as new and desired to he protected hy Letters Patent is set forth in the appended:  
  1. In a lamp housing, particularly for use in photographic projection printers. a light confining and guiding device comprising a plurality of walls movahlc hetween first positions in which said device constitutes a first light duct in the form of a first hollow truncated pyramid with spaced apart top and base planes and contiguous sides which confine light that enters said first duct by passing across one of said planes and issues from said first duct by passing across the other of said planes. and at least one second position in which said device constitutes a different second light duct having the form of a second hollow truncated pyramid with spaced apart top and base planes and contiguous sides the area of at least one of said planes of saidsecond pyramid being different in si/e from the area of the corresponding plane of said first pyramid 2. A light confining device as defined in claim 1. wherein the length of said first light duct. as considered in the direction of the passage of light therethrough. is identical with the length of said second light duct.  
  3. A light confining device as defined in claim I. wherein one of said light ducts is located within the confines of the other of said light ducts.  
  4. A light confining device as defined in claim I. wherein said second light duct has a first open end in one of said planes and a second open end in the other of said planes.  
  5. A light confining device as defined in claim 4. wherein the area of said first end is identical with the area of said one plane and the area of said second end is different from the area of said other plane 6. A light confining device as defined in claim I. wherein said walls constitute portions of the sides of said first light duct.  
  7. A light confining device as defined in claim 6, wherein said walls are pivotahle between said first and second positions about axes which are located in the region of said top plane.  
  8. A light confining device as defined in claim 7. wherein said walls are further movable at right angles to the respective axes in the course of said pivotal movement thereof.  
 9. A light confining device as defined in claim 7.  
 wherein each side of said first light duct further contprises eorner portions flanking the respective all in the first position of such wall.  
  10. A light confining device as defined in claim 9. further comprising a frame which is rigid with said corner portions.  
  II. A light confining device as defined in claim 9. wherein said walls make with said base plane a first angle in said first positions thereof and a second angle in said second positions thereof. said second angle being at least equal to said first angle.  
  12. A light confining device as defined in claim ll. wherein said second angle is greater than said first angle and each side of said first light duct further comprises a sill adjacent to said base plane. e\tending between the respective corner portions and being flush with the respective wall in said first position of the respective all.  
  13. A light confining device as defined in claim I. wherein said walls are rectangular and the crosssectional area of said second light duct is suhstantialh constant from end to end.  
  14. A light confining de\ice as defined in claim I. further comprising means for simultaneoush moving said walls between said first and second positions.  
  IS. A light eonlining device as defined in claim 14. wherein said means for moving conipris s means for biasing each of said walls to one of said positions thereof 16. A light confining device as defined in claim 14. wherein said means for moving comprises followers provided on said walls and means for moving said walls by way of the respective followers.