GB2140571A

GB2140571A - Light mixer

Info

Publication number: GB2140571A
Application number: GB08411901A
Authority: GB
Inventors: Alfred Hengst
Original assignee: Ernst Leitz Wetzlar GmbH
Current assignee: Ernst Leitz Wetzlar GmbH
Priority date: 1983-05-28
Filing date: 1984-05-10
Publication date: 1984-11-28
Also published as: JPH0489944U; IT8467540A1; IT8467540A0; FR2546639A1; IT8453434V0; CH665721A5; IT1179690B; JPS59222828A; GB8411901D0; DE3319399A1; GB2140571B; DE3319399C2; FR2546639B1

Abstract

A transparency 19 to be photocopied is illuminated by a light source which passes through a housing 13 of polyalkene foam with a diffusely reflective inside surface via heat protective filter 15, matt white reflector 16 and two slightly dulled and slightly focusing polymethylmethacrylate lenses 18' and 18. The lenses, which may be plano-convex, concavo-convex or biconvex, in which the outward facing surfaces are more strongly curved than the inward facing surfaces, are of square cross-section and have an air gap 21 of 1 mm between them. <IMAGE>

Description

SPECIFICATION Light mixer The present invention relates to a light mixer especially for a photographic enlarger or copier.

A colour enlarging device with a light mixing chamber in a metal housing is known from DE-OS 2 258 591,the inside walls of which device are lined with solid, white, foamed-out foam panels and which has an outlet opening extending transversely across the base of the housing. Arranged in the outlet opening is a light-permeable, cloudy diffusion or scatter pane without refracting effect, through which light mixed in the chamber is scattered on passage therethrough so that it can subsequently illuminate an image original. The light-permeable scatter pane narrows outwardly from a thick, circularly shaped central part to a thin, circularly shaped rim part and possesses a different degree of diffusion, i.e. the diffusion is stronger in the central part and gradually weakens towards the rim part.In this manner, the reduction in light intensity from the central point of the light beam to the edge parts thereof is partially compensated for. The light losses in this light mixing chamber are, however, appreciable.

An enlarging apparatus is disclosed in DE-OS 28 08 163, in which the centre-to-rim loss of light intensity is compensated for by the use of an annular or circular light source arranged in the proximity of a scatter pane. This apparatus is usable only for black-and-white enlargements, since the required annular light tube provides a discontinuous spectrum.

Finally, a photographic enlarger for black-andwhite or colour materials is known, the light mixing chamber of which carries a light-permeable optical component, designated as "diffusor lens", with scattering properties in the light exit opening. The light yield and the colour homogeneity of this enlarger are good, but the illumination of the edge parts of the image original is below that of the image original centre.

It would thus be desirable to provide a light mixer for a photographic enlarger or copier which, with high light yield and uniform colour distribution, achieves improved illumination compared with known equipment.

According to the present invention there is provided a light mixer comprising a chamber with a light entry opening and a light exit opening, wall means of the chamber being adapted to diffusely reflect light entering the chamber, and at least two lightly dulled lenses having corresponding light diffusing properties and each arranged in the region of the light exit opening and having a convex surface facing outwardly of the chamber.

Preferably, the lenses have substantially the same shape, for which a plano-convex construction is generally preferred. Other possible constructions include concavo-convex and biconvex and in the latter case the convex surface of each lens opposite its outwardly facing surface is preferably less strongly curved. It has also proved to be advantageous if a narrow air gap is present between the lenses, preferably a gap of about 1 millimetre.

The lenses can be of anorganic or organic glass, preferably of slightly dulled polymethylmethacrylate.

An embodiment of the invention will now be more particularly described by way of example with reference to the accompanying drawing, the single Figure of which is a schematic sectional elevation of a light mixer embodying the invention.

Referring now to the drawing, an illumination system for a photographic enlarger or copier comprises a light mixer 10, which is fastened by means of a retaining bracket 11 in the illumination system.

The light mixer 10 comprises a U-shaped carrier 12, at the upper surface of which the retaining bracket 11 is mounted. A box-shaped housing 13 is inserted into the carrier 12 and connected thereto by, for example gluing. In that case, the two limbs of the U-shaped carrier 12 encompass the upper part of the housing 13, which projects downwardly over the limbs of the carrier 12 and partially over the open sides of the same. The housing 13 is produced from polyalkene foam or substituted-polyalkene foam with diffusely reflective inside surfaces.

The carrier 12 and the housing 13 are provided with circular light entry openings 14 and 14', respectively, and a heat protection filter 15 is arranged in the opening 14. Light emitted by a light source (not shown) passes th rough the light entry openings 14 and 14' and impinges on a reflector 16, which is formed by a matt white inside surface of the wall portion of the carrier 12 opposite the opening 14.

The reflective porperties of the reflector 16 are selected so that they approximately correspond to the scattering capability of the inside wall surfaces of the housing 13. In this manner, the light beams are reflected several times in the light mixer and thereby mixed intensively.

The downwardly open end of the housing 13 forms an approximately square light exit opening 17 forthe diffuse light produced in the mixer. Two plano-convex lenses 18 and 18' are arranged in the region of the exit opening 17 in such a mannerthat the convex surfaces of the lens 18 and 18' are directed outwardly, i.e. towards an image original 19. The lenses 18 and 18' are produced from organic glass, for example polymethylmethacrylate. They are slightly dulled and possess diffuse as well as, to a small extent, focusing properties. The two lenses 18 and 18' are formed to be square as seen in the plan view, wherein the lens 18 closest to the image original 19 has somewhat larger dimensions so that its edge portion can be easily fastened to the underside of the housing 13. In addition, the lens 18 is provided on its planar surface at its corners with formed-on webs 20, on which the inner lens 18' is mounted and secured by, for example, gluing. The width of the lens 18' corresponds to the internal dimensions of the housing 13. The height of the webs 20 is so selected that a narrow air gap 21, of about 1 millimetre, is formed between the lenses 18 and 18' in the region of their optical axes.

With negligibly small light loss, the illumination of the edge regions of the image original may be appreciably improved in this manner, whilst the image original centre is lightly damped. It is particularly worthy of note in this case that a more uniform illumination is maintained for all aperture values and that colour homogeneity is improved.

Claims

1. A light mixer comprising a chamber with a light entry opening and a light exit opening, wall means of the chamber being adapted to diffusely reflect light entering the chamber, and at least two lightly dulled lenses having corresponding light diffusing properties and each arranged in the region of the light exit opening and a convex surface facing outwardly of the chamber.

2. A light mixer as claimed in claim 1, wherein at least one of the lenses has a planar surface opposite its convex surface.

3. A light mixer as claimed in claim 1, wherein at least one of the lenses has a concave surface opposite to its convex surface.

4. A light mixer as claimed in claim 1, wherein each of the lenses has a further convex surface opposite to and of lesser curvature than its firstmentioned convex surface.

5. A light mixer as claimed in any one of the preceding claims, wherein the lenses are so arranged closely adjacent to each other as to leave a narrow air gap therebetween.

6. A light mixer substantially as hereinbefore described with reference to the accompanying drawing.

7. A photographic enlarger or copier comprising a light mixer as claimed in any one of the preceding claims.