Illumination – Light source and modifier – Including reflector
Reexamination Certificate
2002-09-12
2004-11-23
Husar, Stephen (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S217060, C362S298000, C362S301000, C362S343000
Reexamination Certificate
active
06821000
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a linear light source, and more particularly to such a linear light source for use in a film scanner.
BACKGROUND OF THE INVENTION
Light integrating chambers for film scanning are known in the prior art. A conventional cylindrical integrating cavity used in a film scanner is shown in FIG.
1
. As currently used as linear light sources in many film scanners, light from a lamp
12
and a lens
14
is directed into a hole
16
in a cylinder wall of an integrating cylinder
10
. The light reflects many times against the white interior chamber wall of the cylinder
10
to randomize its distribution. This randomization is intended to produce uniform, diffuse light within the cylinder
10
, which then exits through a long, narrow exit slit
18
to produce a stripe of uniform, diffuse illumination applied against a surface of an original material, such as a film
20
. The light passing through the film
20
is modulated in intensity by the density varying image on the film and focused by a lens system
21
on a sensor array
24
.
It is desirable to produce a highly intense, uniform and lambertian line source of illumination for use in a film scanner application. A further requirement for an illumination system is that the efficiency be as high as possible while still providing the desired uniformity and diffusion. This can be achieved by designing the cavity to have the highest possible reflectivity of the walls and the minimum possible area for the introduction of the light. Bulk diffusers such as Spectralon currently have the lowest loss of available reflective diffuse materials. Furthermore, an integrating cylinder apparatus that allows a small interior surface area and entrance hole area while maintaining a desired intensity profile by using a light pipe to couple light into the cavity has been disclosed in U.S. Pat. No. 5,274,228 (M. Kaplan). As shown in
FIG. 2
, this type of illuminator allows light into a cylindrical cavity
34
via a glass rod
22
which is positioned along the longitudinal direction of the cylindrical cavity
34
. Light
28
enters the rod
22
at one end
26
and then propagates inside the rod via total internal reflection (TIR) towards the opposite end
29
of the rod. The rod is given a surface treatment
30
that disrupts the TIR and diffusely leaks light
32
into the cavity interior where it is diffused further and eventually finds its way out the exit slit
18
. The amount of light released into the cavity interior at any particular spot then is roughly proportional to the degree or width of the surface treatment
30
but is also influenced by the characteristics of the input light angular component.
The method of the '228 patent performs well when the input light contains a wide range of input angles as the higher angled light more easily exits the rod at the surface treatment
30
than does shallow angled light. This effect implies that after light has traveled down the length of the rod much of its higher angled light exits the rod leaving a more collimated beam at the end of the rod. Further, it implies that there is still a substantial amount of light at the end of the rod which if allowed to flood the end of the cavity would produce a bright spot at the end of the cavity. It is desirable then to diffusely reflect this lower angled light using a reflecting mirror
36
at the end of the rod back into the rod for another chance of exiting the rod in more useful locations along the rod. (Alternatively, the mirror
36
may be replaced by a white, diffusely reflecting surface spaced at least a few wavelengths of light away from the end of the rod.) The act of diffusing the light at the end of the rod redistributes the angular components so as to produce more higher angled light which has a better chance at exiting the rod at locations along its surface treatment.
Furthermore, it is desirable to be able to attenuate the intensity of the output light from the illuminator without undue adverse effects on the spatial profile exiting the illuminator slit. The range of desired attenuation is typically somewhere around five to six F-stops. This is accomplished by attenuating the light before it enters the cavity via its glass rod component. According to this method of attenuation, a pair of movable V-shaped blades
34
(see
FIG. 2
) are placed in the light path so as to provide a means of varying the amount of light passing through the aperture. In so doing, the collection of input light path angles becomes truncated as the aperture is closed down. This causes a change in the source light angular component entering the integrator cavity. Changing the aperture opening varies the amount of light likely to reach the end of the rod and thus also effects the spatial profile as a function of the aperture opening. This is an undesirable effect. In most scanners that use the known types of illuminators, however, the problem is unaddressed because they do not require attenuation of the light source.
As mentioned above, the concept of diffusely reflecting light back into the rod is generally disclosed in the '228 patent; however, the disclosed concept involves drawbacks that are neither identified nor described. For example, by not holding/capturing the end of the rod or by allowing a space between the end of the rod and the far end of the cavity interior, a bright spot is generated at the far end of the cavity due to excessive flooding with light. Conversely, attempting to capture the end of the rod in a bore slightly bigger than the rod provides no support for the rod and still allows some flooding to occur. Attempting to capture the end of the rod inside a bore of the same size as the rod where the rod snugly fits into the bore fails when the tolerance of the diameter of the rod exceeds the diameter of the bore; a slightly oversized rod will not fit into the bore. Furthermore, when a high power light source is used, a considerable amount of energy reaches the end of the rod and may damage the diffusely reflective material/coating at the surface of the cavity if insufficient cooling is provided such as forced air injected into the cavity. If the end of the rod is captured in a snug fitting bore there is little chance of circulating cooling air to get around the end of the rod.
Currently, illuminators that use glass rods in cavities use various techniques to hold the rod inside the cavity. A) As shown in
FIG. 2
, some designs use no interior end holding feature; the rod is held at the input end only. This means that the (cavity interior) end of the rod is free to wiggle or bottom out via gravity to the bottom of the cavity. This method has been used where the cavity is only slightly larger (in diameter) than the rod and when the design does not need to operate over a wide range of attenuation. Often, no special attention is given to recoupling the light at the end of the rod other than its close proximity to the end wall (of diffusely reflective material). B) At least one other design uses a “V” shaped end feature to help center the rod at the end of the cavity and provide a minimal contact to the rod material. Again, this design does not require a wide range of attenuation, as does the design mentioned above. Also, when using a “V” shaped feature, there is no guarantee that the rod, due to length tolerances, will in fact engage the “V” shaped edges. Usually the input end of the rod is constrained to a particular dimension/position and the far end of the rod (inside the cavity) is allowed to vary in position due to the rod length tolerances. C) Some designs have attempted to use a bore in the end face wall of the cavity to allow the rod to fit inside the bore. The problem with this design is that if the bore is selected to have a diameter the same as the rod diameter then some rods will not fit into the bore if they are slightly over-sized. Conversely, if the rod diameter is less than the diameter of the bore, then the rod is in effect not held or constrained.
SUMMARY OF THE INVENTION
The present invention i
Meiers Ronald E.
Russel William H.
Cranson James W
Eastman Kodak Company
Husar Stephen
Shaw Stephen H.
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