GB1588155A - Photographic enlargers - Google Patents

Description

(54) IMPROVEMENTS IN PHOTOGRAPHIC ENLARGERS (71) We, OPTIGON RESEARCH AND DE VELOPMENT CORPORATION, P.O. BOX 1740, Santa Monica, California, United States of America, a corporation organised and existing under the laws of the State of California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment :- This invention relates to photographic enlargers.

In a photographic enlarger, where it is desirable to provide light having an optimum intensity over the entire printing area while maintaining a uniform distribution of the intensity and color of the light to obtain sharp enlargements in a minimum exposure time, it is usual to employ a light mixing device. Preferred exposure times are generally on the order of less than 15 seconds.

Modern color enlargement systems heretofore have comprised a tungstem halogen lamp having an integral heat transmitting reflector, a plurality of dichroic filters individually variably movable into the light path to permit color corrections required for the variable color sensitivities of the various photographic print papers and chemicals used therewith, a hollow reflective chamber to mix the light and diffusers to provide a uniform intensity and color distribution. Such enlargers may also be used, generally without the filters, to provide black-and-white prints and enlargements.

In the described enlargers only about ten percent of the power supplied to the lamp is available as light, the remainder being dissipated as heat and other losses. The efficiency of the optics between the lamp and the printing paper is generally less than one percent.

Therefore, in order to produce acceptable prints in the desired exposure time, a lamp having a high light output and a similarly high wattage is required.

Such a high wattage lamp, however, requires a cooling apparatus such as a forced air cooling system to dissipate the heat generated by the lamp. This adds to the expense of the enlarger, requires an enlarger of an increased size, and may result in the production of unsharp images due to the vibration introduced by the cooling system.

It is therefore desirable to provide an optical device, and particularly a light mixing device, of increased efficiency. In U.S. Patent No.

4,125,315, entitled "Light Mixing Apparatus", granted on an application filed by R. Altman and R. Badkar, and assigned to the assignee of the present invention, a light mixing device is disclosed that efficiently and uniformly mixes light; however, it requires the use of several lengths of optically clear pipe fitted together to provide a plurality of surfaces to allow for more reflections within the optical system and increasing uniformity of the mixing.

The present invention consists in a photographic enlarger comprising a light source, a light mixing device comprising a solid rodlike member of an optically clear material, said member having a longitudinal axis, smooth peripheral walls, first and second end surfaces, a id a length of at least three and one-half times its diameter, light from said source being directed on to said first end surface so that the light travels generally axially through said member, wherein light is internally reflected by said smooth peripheral walls and mixed along the length of said member, and light exits through said second end surface, and means on said peripheral walls adjacent said second end surface for refracting light therethrough so that the pattern of light on a given area disposed below said second end surface approaches a Lambertian distribution.

One embodiment of the invention provides a photographic enlarger which includes a light mixing device of high efficiency which is capable of producing uniform intensity and color distribution with a much shorter length of pipe.

Briefly stated, the embodiment comprises a substantially rod-like elongated light trans mitting member through which light is transmitted and mixed by internal reflection off its peripheral walls. Light is directed into the member at one end from a direction transverse to the axis thereof and is reflected from an angled end surface and reflector generally axially through the member. The member has a light diffusing surface at the light exit end and in a region of the peripheral wall contiguous thereto. Light diffusing means is provided between the lamp and the light entrance end of the light pipe to randomly diffuse and scatter the light from the lamp before it enters the light pipe, to increase the number of internal reflections of the light off the peripheral wall as it travels through the member.

Other embodiments are disclosed wherein the light is directed to intersect the rod-like member's longitudinal axis outside the member. The apparatus may further include an elbow member for receiving the light, curving it and directing it generally axially toward and longitudinally through the rod-like member.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a front elevational view, partially cut away, of a photographic enlarger head embodying the invention; Fig. 2 is a view along section lines 2-2 of Fig. 1; Fig. 3 is an elevational view of a light mixing member in the enlarger of Fig. 1; Fig. 4 is an end view of the light mixing member of Fig. 3; Fig. 5 is a view of a modification of the member shown in Fig. 3, as shown from the right thereof; Fig. 6 is a view of the member as shown in Fig. 4 as seen from the opposite side thereof; Fig. 7 is a side elevational view of a part of a second embodiment of the invention having a straight light pipe and an elbow member for curving the light and directing it thereto; and Fig. 8 is a side elevational view of a modification of the elbow member shown in Fig. 7.

An enlarger 10 embodying the invention as shown in Fig. 1, includes a housing 11 having a mounting plate 12 which divides the head into a forward portion 13 and a rear portion 14.

Rear portion 14 houses a lamp 15 having a reflecting surface 16 which serves to direct and focus the light towards a light mixing system 17. The forward portion 13 of housing 11 includes lower portion of light mixing device 17, a condensing lens 18 which directs light from the light mixing apparatus 17 toward a film slide 19 and a focusing lens 20 at the forwardmost end of adjustable bellows 21.

If the enlarger 10 is of the type for making color reproductions, a plurality of dichroic filters 22, 23 and 24 are mounted between lamp 15 and mixing system 17. The filters are individually pivotal about axis 25, movable into or out of the light path by conventional linkages indicated at 26 by means of operator-controlled dials 27, 28 and 29.

Calibrated adjustments are provided to permit the operator to dial in a given amount of correction of the selected color(s). A heat mirror 30 is situated between the dichroic filters in lamp 15 to reflect infrared light generated by the lamp while permitting visible light to pass therethrough, thereby deflecting a substantial amount of heat generated by lamp 15. The heat mirror is angled with respect to the incident light so as to direct the heat away from lamp 15 and not cause it to become unduly warm.

In accordance with the invention, a new and improved light mixer 17 is disposed between the filters and condenser 18. The light mixer includes a rod-like member 31 of an optically clear material having a circular cross-section, a light diffusing element 32 supported by bracket 33 between member 31 in the filters for diffusing light from lamp 15 before it enters member 31, and a reflector 34, also supported on portion 34a by bracket 33. Bracket 33 has an aperture 35 which allows light to pass therethrough while blocking stray light which might enter member 31 without passing through the filters.

Portion 34a is cut out about aperture 35.

As shown in Figs. 1 and 3, member 31 has an upper surface 36 angled with respect to the axis of member 31, a lower exit surface 37 which is ground to diffuse light transmitted from element 31, and a peripheral wall 38 which is smooth except for a ground annular diffusing portion 39 contiguous to lower surface 37. Lower surface 37 is ground to diffuse light exiting therefrom and provide final mixing. The intensity of the light emitted from surface 37 is non-Lambertian. Accordingly, annular portion 39 is made diffusing so that light internally incident on this portion will be refracted through the peripheral wall and mitigate the non-Lambertian properties of surface 37. Member 31 has sufficient length to permit several internal reflections to provide for adequate mixing. A minimum length to diameter ratio of approximately three and one-half to one appears to be necessary for a sufficient number of reflections to achieve adequate mixing. The mixing efficiency of member 31 shows no great increase with increasing length as the length to diameter ratio increases beyond six to one. A length to diameter ratio of approximately five to one appears to be best, considering the optimum amount of mixing desired and space considerations.

With reference to Fig. 1, reflector 34 overlays top surface 36. Reflector 34 has a highly reflective surface, and is opaque bit it is not critical that it be flat. Reflector 34 and top surface 36 cooperate to reflect light from aperture 35 generally axially through member 31. Any light exiting surface 36 is reflected into member 31 by reflector 34.

Member 31 is mounted through plate 12 by bracket 40 which includes a hub 41 inserted from rear portion 14 of housing 11 and is fixed to mounting plate 12 bu nut 42. A split slip ring 43 rests in the well of hub 41 and compressively engages member 31 at two annular areas of contact. The annular areas are maintained relatively small to minimize generation of heat thereat. Retaining ring 44 holds slip ring 43 in the well tight against member 31. Member 31 is thus vertically adjustable for alignment purposes.

The optical axis of the enlarger extends from the center of the lamp, the center of aperture 35 in bracket 33, the center of surface 36, the axis of member 31, and the center lines of condenser 18 and lens 20.

A modification of member 31 is shown in Figs. 5 and 6. The light entrance portion 46 of peripheral wall 38 near the top of member 31 is ground to diffuse the entering light from lamp 15 and the filters. In this configuration, diffusing plate 32 is not necessary. In the ground region 46, the entire circumference of peripheral wall 38 is ground as a manufacturing expediency, although only the light facing portion need be ground.

In operation, visible light from lamp 15 passes through heat mirror 30, along the optical axis defined above. Heat mirror 30 reflects the infrared light and heat away from mixer 17. The visible light passes through filters 22, 23 or 24 as may be placed in its path by the operator. The light then passes through the aperture in bracket 33, through diffuser 32, and enters the light entrance portion 46 of member 31. The diffused light is reflected from surface 36 and reflector 34 and is directed thereby generally axially through member 31. The light is efficiently mixed by internal reflections off peripheral wall 38.

The light is then refracted from member 31 at its lower surface 37 and through the contiguous diffusion portion 39 of peripheral wall 38.

The member 31 may be of any suitable optically clear material which will withstand the heat from lamp 15. Examples of such material are glass, methylmethacrylate and polycarbonate. The surface 36 is preferably 45" with respect to the axis of member 31 for manufacturing and alignment purposes. However, other angles may be chosen and be within the scope of the invention.

In a typical embodiment of the invention, the lamp is positioned to focus on the middle filter, which is yellow, the others being cyan and magenta. The member 31 is five inches long overall, and one inch in diameter. End surface 37 and contiguous wall 39 are made diffusing by sandlbasting with one hundred mesh grit. The diffusing member 32 need have only one diffusing surface, preferably on the side towards member 31. The length of diffusing wall portion 39 is one-half inch. The hot mirror 30 may be of commerical grade glass sold under the Registered Trade Mark "Pyrex".

In another embodiment of the invention the portion of the member 31 just below the angle surface 36 may be cut square. The light passing diffuser 32 is then reflected from reflector 34 into a square cut first end of member 31.

With reference to Figure 7, a second embodiment of the invention includes a light pipe 311 of an optically clear material. Light pipe 311 has a top surface 361 cut square and perpendicular to the length direction of the light pipe. Light pipe 311 further has peripheral walls 381, a diffusing lower end 37 and a diffusing annular region 39. The embodiment further includes a tubular elbow pipe member 50 which includes a curved body or shank portion 51, an exterior peripheral wall 52 and an interior peripheral wall 52a. Elbow 50 has a first open end 53 facing lamp 15 and a second open end 54 proximate to, and preferably surrounding, upper end surface 361.

Light from lamp 15 enters the elbow 50 through first open end 53, is reflected off interior peripheral wall 52a and is directed toward entrance end 361 of light pipe 311 in a direction generally axially toward light pipe 311. The reflection of the light off the interior peripheral wall 52a also provides a preliminary mixing of the light before it enters light pipe 311. Interior peripheral wall 52a is preferably aluminized or painted white to enhance the reflection of the light therefrom.

The elbow 50 as well as modified elbow 501 of Figure 8 may be a conventional polyvinyl chloride pipe fitting.

Diffusing plate 32 may be used with this embodiment. However, plate 32 need not be provided if end 54 is made sufficiently diffusing by, for example, blasting end 54 with 100 mesh grit.

With reference to Figure 8, a modified elbow 501 is provided with a flat reflecting mirror 55 disposed at a 45" angle to both end 53 and end 54. Reflector 55 is situated so as to reflect light from end 53 through end 54 to the light pipe. The interior peripheral wall 52al, except reflector 55, is preferably aluminized or painted white to enhance the light reflective properties thereof. A diffusing plate 32 is also preferably used in conjunction with and ahead of modified elbow 501.

The plate 32 may be deleted if end 54 is made diffusing, as with elbow 50.

WHAT WE CLAIM IS: 1. A photographic enlarger comprising a light source, a light mixing device comprising a solid rod-like member of an optically clear material, said member having a longitudinal axis, smooth peripheral walls, first and second

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. aperture 35 generally axially through member 31. Any light exiting surface 36 is reflected into member 31 by reflector 34. Member 31 is mounted through plate 12 by bracket 40 which includes a hub 41 inserted from rear portion 14 of housing 11 and is fixed to mounting plate 12 bu nut 42. A split slip ring 43 rests in the well of hub 41 and compressively engages member 31 at two annular areas of contact. The annular areas are maintained relatively small to minimize generation of heat thereat. Retaining ring 44 holds slip ring 43 in the well tight against member 31. Member 31 is thus vertically adjustable for alignment purposes. The optical axis of the enlarger extends from the center of the lamp, the center of aperture 35 in bracket 33, the center of surface 36, the axis of member 31, and the center lines of condenser 18 and lens 20. A modification of member 31 is shown in Figs. 5 and 6. The light entrance portion 46 of peripheral wall 38 near the top of member 31 is ground to diffuse the entering light from lamp 15 and the filters. In this configuration, diffusing plate 32 is not necessary. In the ground region 46, the entire circumference of peripheral wall 38 is ground as a manufacturing expediency, although only the light facing portion need be ground. In operation, visible light from lamp 15 passes through heat mirror 30, along the optical axis defined above. Heat mirror 30 reflects the infrared light and heat away from mixer 17. The visible light passes through filters 22, 23 or 24 as may be placed in its path by the operator. The light then passes through the aperture in bracket 33, through diffuser 32, and enters the light entrance portion 46 of member 31. The diffused light is reflected from surface 36 and reflector 34 and is directed thereby generally axially through member 31. The light is efficiently mixed by internal reflections off peripheral wall 38. The light is then refracted from member 31 at its lower surface 37 and through the contiguous diffusion portion 39 of peripheral wall 38. The member 31 may be of any suitable optically clear material which will withstand the heat from lamp 15. Examples of such material are glass, methylmethacrylate and polycarbonate. The surface 36 is preferably 45" with respect to the axis of member 31 for manufacturing and alignment purposes. However, other angles may be chosen and be within the scope of the invention. In a typical embodiment of the invention, the lamp is positioned to focus on the middle filter, which is yellow, the others being cyan and magenta. The member 31 is five inches long overall, and one inch in diameter. End surface 37 and contiguous wall 39 are made diffusing by sandlbasting with one hundred mesh grit. The diffusing member 32 need have only one diffusing surface, preferably on the side towards member 31. The length of diffusing wall portion 39 is one-half inch. The hot mirror 30 may be of commerical grade glass sold under the Registered Trade Mark "Pyrex". In another embodiment of the invention the portion of the member 31 just below the angle surface 36 may be cut square. The light passing diffuser 32 is then reflected from reflector 34 into a square cut first end of member 31. With reference to Figure 7, a second embodiment of the invention includes a light pipe 311 of an optically clear material. Light pipe 311 has a top surface 361 cut square and perpendicular to the length direction of the light pipe. Light pipe 311 further has peripheral walls 381, a diffusing lower end 37 and a diffusing annular region 39. The embodiment further includes a tubular elbow pipe member 50 which includes a curved body or shank portion 51, an exterior peripheral wall 52 and an interior peripheral wall 52a. Elbow 50 has a first open end 53 facing lamp 15 and a second open end 54 proximate to, and preferably surrounding, upper end surface 361. Light from lamp 15 enters the elbow 50 through first open end 53, is reflected off interior peripheral wall 52a and is directed toward entrance end 361 of light pipe 311 in a direction generally axially toward light pipe 311. The reflection of the light off the interior peripheral wall 52a also provides a preliminary mixing of the light before it enters light pipe 311. Interior peripheral wall 52a is preferably aluminized or painted white to enhance the reflection of the light therefrom. The elbow 50 as well as modified elbow 501 of Figure 8 may be a conventional polyvinyl chloride pipe fitting. Diffusing plate 32 may be used with this embodiment. However, plate 32 need not be provided if end 54 is made sufficiently diffusing by, for example, blasting end 54 with 100 mesh grit. With reference to Figure 8, a modified elbow 501 is provided with a flat reflecting mirror 55 disposed at a 45" angle to both end 53 and end 54. Reflector 55 is situated so as to reflect light from end 53 through end 54 to the light pipe. The interior peripheral wall 52al, except reflector 55, is preferably aluminized or painted white to enhance the light reflective properties thereof. A diffusing plate 32 is also preferably used in conjunction with and ahead of modified elbow 501. The plate 32 may be deleted if end 54 is made diffusing, as with elbow 50. WHAT WE CLAIM IS:

1. A photographic enlarger comprising a light source, a light mixing device comprising a solid rod-like member of an optically clear material, said member having a longitudinal axis, smooth peripheral walls, first and second

end surfaces, and a length of at least three and one-half times its diameter, light from said source being directed on to said first end surface so that the light travels generally axially through said member, wherein light is internally reflected by said smooth peripheral walls and mixed along the length of said member, and light exits through said second end surface, and means on said peripheral walls adjacent said second end surface for refracting light therethrough so that the pattern of light on a given area disposed below said second end surface approaches a Lambertian distribution.

2. A photographic enlarger as claimed in claim 1, further including a reflecting member disposed between said light source and said light mixing device, the reflecting member directing the light from said source on to said first end surface of said light mixing device.

3. A photographic enlarger as claimed in claim 1 or 2, further including means for diffusing the light entering said rod-like member.

4. A photographic enlarger as claimed in claim 2, further including means for diffusing the light entering said rod-like member, the diffusing means being positioned between said light source and the reflecting member.

5. A photographic enlarger as claimed in any one of claims 1 to 4, further including a condensing lens disposed to receive light which exits from said second end surface and said means on said peripheral walls adjacent said second end surface.

6. A photographic enlarger as claimed in any one of the preceding claims, where said first end surface is made light diffusing.

7. A photographic enlarger according to claim 2, in which a hollow housing member is disposed over said first end surface, and said reflecting means is disposed within said hollow housing member.

8. A photographic enlarger as claimed in any one of claims 1 to 7, further comprising a plurality of filter means disposed between said source and said first end surface for adjusting the color content of the light directed on to said first end surface.

9. A photographic enlarger as claimed in any one of claims 1 to 8, wherein said peripheral walls adjacent said second end surface comprise an annular light diffusing area defined on said peripheral walls.

10. A photographic enlarger as claimed in any one of claims 1 to 9, further comprising a housing having a partition therein defining upper and lower compartments, said mixing device extending through said partition, means supporting said rod-like member in said housing and through said partition, said supporting means having minimal contact on said light mixing device, said light source and said first end surface being positioned in said upper compartment.

11. A photographic enlarger as claimed in claim 1, further comprising a mask disposed between the light source and said first end surface, said mask having a light transmitting opening of a smaller diameter than said rodlike member.

12. A photographic enlarger as claimed in any one of claims 1 to 11, wherein said refracting means is an annular diffusing band defined on said peripheral wall contiguous said second end surface, and said second end surface is light diffusing.

13. A photographic enlarger as claimed in any one of claims 2 to 12, wherein said reflecting member is a mirror disposed at substantially 45" to said longitudinal axis.

14. A photographic enlarger constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.