CONTINUOUSLY VARIABLE OPTICAL FILTER DEVICE

Abstract: Filter than can be adjusted to transmit varying amounts of light, and characterized by uniform degree of transparence over its entire working portion. One embodiment of said filter includes an elongated, flexible, semi-transparent strip (10) having a linearly varying degree of transparence, a pair of reels (14 and 16) around which the ends of the strips are wound, and three of roller bearings (18, 20 and 22) for supporting the strip in a doubled over manner between a light source (30) and a target surface (32). A knob (24) is adjusted to align different portions of the doubled over strip and thus vary the composite degree of transparence of the filter.

Description: -1- DP sc r i pt i on Continuously Variable Optical Filter Pevice Technical Field My invention relates generally to optical filters, and more particularly to filters used transmit incident light at a reduced intensity. Certain characteristics of light can be modified by an optical filter. Some filters polarize an incident " beam of light, others transmit only certain frequencies of light, and yet others uniformly reduce the intensity of all of the spectral components of an incident beam of light. Those filters which reduce the intensity of an incident beam are useful for a variety of purposes, such as dimming the light transmitted by the lamp of a photo¬ graphic enlarger. Some filters can be adjusted to vary the amount of light that they will transmit. Background Art There are numerous types of variable filters known to the prior art. One type includes an elongated strip provided with discrete sections having different optical properties. Another type includes an elongated semi-transparent strip having optical properties which vary continuously along the length of the strip. Each of these types of variable filters have their own advantages and disadvantages. United States patent 3,603,672 of Bes ide teaches a device of the first type and includes an elongated film strip extending between two reels. The film strip has sections along its length which have 'different degrees of opacity or different colors'. In a preferred embodiment of his invention a pair of his film strip filters are attached in front of the lenses of a pair of sunglasses. Similar devices of the first type are described in United Patents 2,444,512 of N. Kath. and 3,483,808 of G. Arnold. The second type of variable filter is exemplified by the device described in United States patent 2,120,499 of R. Mackay which includes a plurality of strip filters of different colors and variable opacities. By adjusting the relative positions of the various strip filters different light intensities and colors are produced. The first type of variable filter suffers from the disadvantage that the transmitted light cannot be varied continuously, but only in discrete quanta corresponding to the separate filtering sections. The second type of variable filter may be varied continuously, but does not transmit light of a uniform intensity over its entire working surface. Disclosure of the Invention In accordance with the present invention, I provide a long, semi-transparent strip having a degree of transparence that varies continuously and linearly along its length, and a structure for supporting the strip between a light source and a target surface. The support structure includes a' bearing surface around which the strip is trained so as to double back upon itself. Thus, light emitted by the light source radiates through a doubled over portion of the strip. The semi-transparent characteristics of two aligned portions of the doubled over strip combine to produce a uniforn composite transparence. This uniform composite transparence can be varied by adjusting the strip so as to change the aligned portions. Other embodiments of this invention include an elongated strip as described above held in alignment with a fixed filter plate, or a pair of mutually adjustable filter plates. My invention is advantageous in that an optical filter is provided which is both continuously variable and which has a uniform composite transparence along its entire working surface. Brief Description of the Drawings 5 The details of my invention will be described in connection with the accompanying drawing, in which Fig. 1 is a perspective view of my device being utilized with a photographic enlarger set-up; Fig. 2 is a simplified side elevational view of a first embodiment of the filter; 10 Fig. 3 is a pictorial representation of the filter used for the purpose of describing the operating principles of this invention; Fig. 4 is a simplified side elevational view of a series of colored filters in accordance with this invention; and Fig. 5 is a simplified sice eleva- -^ • tional view of a second embodiment of my device having a fixed filter and a movable strip filter. Best Mode for Carrying Out the Invention Referring to Fig. 1 of the drawing, a variable filter constructed in accordance with my invention 0 includes an elongated, flexible, semi-transparent strip 10 having a linearly varying transparence (i.e. optical density) along its length. By 'linearly varying' it is meant that the amount of light transmitted through a portion of the filter from a fixed light source is a 5 linear function of the position of that portion on the strip. The filter also- includes a support structure 12 having a first closed reel 14, a second closed reel 16, and a number of roller bearings 18, 20, and 22. A first 0 end of the strip is attached to reel 14, intermediate portions of the strip are trained over the roller bearings, and the second end of the strip is attached to reel 16. An adjustment knob 24 is attached to reel 14 and a belt 26 couples the two reels together for mutual V. ' IPO K >r . " rotation. • Also shown in Fig. 1 is a photographic enlargement head 28, a light source 30, an exposure table 32 (the target surface) , and a piece of photographic print paper 34 supported by table 32. The enlargement head, exposure table, and photographic paper are included in this figure for descriptive purposes and to illustrate a particular use for the present device. It should be apparent throughout this description, however, that the present filter can be used between any light source and target surface. As indicated by. broken line 36, the support structure can be coupled to the enlargement head 28, or, as indicated by broken line 38, the support structure can be attached to table 38. The particular method of attachment is not critical as long as the filter is held between the light source and the optical surface in a stable manner. As can be seen in this figure, the strip is trained over the roller bearings so as to form a double thickness. Since the transparence or optical density of the strip varies linearly along its length, the composite transparence of the double thickness of the strip has a uniform transparence along the aligned length. This composite transparence can be varied by aligning different portions of the strip. In the present embodiment this is accomplished by rotating knob 24 in a clockwise or counter clockwise direction. In Fig. 2 an alternate construction for the support structure is shown to include an elongated, transparent or semi-transparent plate 42 disposed between the doubled over strip 10'. Again, the rotation of the reels 14' and 16' adjusts the degree of composite transparence of the filter. The alternate embodiment of Fig. 2 is advantageous in that it can be made thin enough to fit within the filter slot of the enlargement head. Furthermore, as will be dicussed again later, the plate 42 may be tinted to provide a continuously variable colored filter. The operation of the present device will be discussed with reference to Fig. 3 where a doubled over filter strip 46 is placed between a light source 44 (in this case an incandescent light bulb) and a target surface 48 (here shown as an eye) . A series of points along the strip have been numbered to indicate the relative transparence of the strip at that point. For example, the optical density at point 5 is 2-1/2 times the optical density at point 2, and allows only 2/5 the amount of light to be transmitted therethrough. As can be seen, due to the linearly varying transparence of the strip, the amount of light reaching target surface 48 from the light source is the same as if a fixed sheet filter of relative value 8 were placed therebetween. If the strip were re-adjusted so that point 1 was in alignment with point 6 the filter would be optically identical to a fixed sheet filter of relative value 7. In Fig. 4, an assembly of variable density filters 50, 52, and 54 are disposed between a light source 56 and a target surface 58. These filters are tinted the primary colors as indicated and linearly vary in transparence as described above. An assembly such as this is useful in the production of color prints. In Fig. 5 an alternate embodiment of this invention is shown to include a movable first strip 60 having a linearly varying transparence, and a fixed second strip or plate 62 having a linearly varying transparence which varies as the inversely with respect of strip 60. The two strips are held in alignment between a light source 64 and an optical surface 66 . The composite transparence of the filter can be varied by moving strip 60 back and forth with strip 62 held immobile. Of course, strip 62 could also be moved to vary the composite translucence of the filter. Another embodiment of the present invention includes an endless loop filter having the above described linearly varying transparence and having a doubled portion as described above. Yet another embodiment includes an associated pair of filter strips or plates each having linearly varying transparencies. It is intended that the appended claims include all such embodiments of this filter as fall within the true spirit and scope of this invention.

Claims: Cl aims 1. A continuously variable optical filter device comprising: a first semi-transparent portion lying in a first plane; a second semi-transparent portion lying in a second plane substantially parallel to said first plane and aligned with said first portion; and means for moving said first portion back and forth along a line of motion in said first plane; where said first portion has an 0 optical density that varies as a continuous linear function in the direction of said line of motion, and said second portion has an optical density that varies as the inverse of said continuous linear function in the direction of said line of 5 motion. 2. The filter device of claim 1 additionally comprising means for supporting said first portion and said second portion between a light source and a target surface. 0 3. The filter device of claim 2 wherein said second portion is a fixed plate. 4. The filter device of claim 2 wherein said second portion is a plate movable back and forth along a line of motion in said second plane that is 5 substantially parallel to the line of motion lying in said first plane. 5. The filter device of claim 3 or 4 wherein said first portion is an elongated, flexible strip, and wherein said supporting means includes a reel ° mechanism for moving said strip back and forth along said line of motion. 6. The filter device of claim 2 wherein said first portion and said second portion are spaced apart portions of a single, elongated, flexible strip having an optical density which varies linearly along its length, said strip being trained back upon itself whereby light emitted by said source radiates through both said first portion and said second portion before impinging on said target surface. 7. The filter device of claim 6 wherein said supporting means includes a reel mechanism for moving said strip back and forth along said lines of motion.

Inventors: KLAPKIW JOHN, KLAPKIW KATHERINE
Applicants: KLAPKIW JOHN, KLAPKIW KATHERINE
Application year: 1981
Main classification: G02B5
IPC codes: G02B7, G03B27