U.S. patent number RE35,310 [Application Number 07/961,510] was granted by the patent office on 1996-08-06 for color corrected projection lens.
This patent grant is currently assigned to U.S. Precision Lens Incorporated. Invention is credited to Jacob Moskovich.
United States Patent |
RE35,310 |
Moskovich |
August 6, 1996 |
Color corrected projection lens
Abstract
A projection lens in which a lens unit which may comprise one or
two elements is closely coupled at the object end of the lens to a
cathode ray tube. At the image end is a lens unit of overall weak
optical power which comprises from the image end a first positive
element followed by a closely spaced negative element of
substantially higher dispersion. Intermediate the object side lens
unit and the image side lens unit is a lens unit of substantial
optical power supplying substantially all of the positive optical
power of the lens. Closely spaced to this power lens unit on the
object side is a negative lens element of high dispersion. This
negative lens element may be considered to be part of the power
lens unit. The negative lens elements have weak optical power at
the axis of the lens but are of generally increasing negative
optical power from the optical axis to the clear apertures of the
negative lens elements to contribute to proper color correction of
the lens, particularly axial chromatic aberration adjacent the full
aperture. The intermediate positive power lens unit may comprise
one or two positive elements depending upon the application and the
manner in which the power is to be distributed to minimize
aberrations. A lens embodying the invention is capable of
maintaining a high image quality over a large range of
magnifications by moving the first and second lens units from the
image end in predetermined differential relationship.
Inventors: |
Moskovich; Jacob (Cincinnati,
OH) |
Assignee: |
U.S. Precision Lens
Incorporated (Cincinnati, OH)
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Family
ID: |
23594609 |
Appl.
No.: |
07/961,510 |
Filed: |
October 15, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
403139 |
Sep 5, 1989 |
04963007 |
Oct 16, 1990 |
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Current U.S.
Class: |
359/649; 359/650;
359/651; 359/715; 359/716; 359/754 |
Current CPC
Class: |
G02B
9/12 (20130101); G02B 13/18 (20130101) |
Current International
Class: |
G02B
13/18 (20060101); G02B 9/12 (20060101); G02B
003/02 (); G02B 013/18 () |
Field of
Search: |
;359/648-651,708,713-716,764,784,791,754-756,757,763 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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59-170812 |
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Sep 1984 |
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JP |
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59-17082 |
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Sep 1984 |
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JP |
|
593514 |
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Oct 1947 |
|
GB |
|
1269133 |
|
Apr 1972 |
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GB |
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Other References
Kingslake, R., Lenses In Photography, Garden City Books, 1951, pp.
131-132. .
Smith, W., "Optical Materials and Coatings," Modern Optical
Engineering, McGraw Hill, 1966, pp. 145-155..
|
Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Phan; James
Attorney, Agent or Firm: Klee; Maurice M.
Claims
What is claimed is:
1. A projection lens for a cathode ray tube comprising a rear lens
unit .[.adopted.]. .Iadd.adapted .Iaddend.to be closely coupled to
a cathode ray tube at the object end thereof, said lens unit having
a strongly concave image side surface,
a front lens unit on the image side of said lens .[.comprising.].
.Iadd.consisting of .Iaddend.a positive image side element having a
dispersion similar to the dispersion of crown glass followed by a
closely spaced negative element of high dispersion similar to the
dispersion of flint glass, and
another lens unit providing substantially all of the positive
optical power of said lens intermediate said front and rear lens
units, said another lens unit including a negative element of high
dispersion similar to the dispersion of flint glass on the object
side thereof.
2. The lens of claim 1 where said another lens unit comprises two
positive elements both having spherical surfaces.
3. The lens of claim 1 further including a corrector lens unit of
weak optical power having at least one aspherical surface
positioned between said rear lens unit and said another lens unit
so that the axial marginal rays from the long conjugate side of
said lens intersect said corrector lens unit below the clear
aperture thereof.
4. The lens of claim 3 where said front lens unit and said another
lens unit move in fixed relation and said rear lens unit together
with said corrector lens unit move in fixed relation but
differentially with respect to said front lens unit and said
another lens unit to vary the focal length of said lens.
5. The lens of claim 1 where the absolute value of the optical
power of said negative lens element of said front lens unit
increases from the optical axis to the clear aperture thereof due
to at least one aspheric surface thereof.
6. The lens of claim 1 where said lens elements of said front lens
unit contribute to correction of axial chromatic aberration
adjacent the clear aperture thereof.
7. The lens of claim 1 where the elements of said another lens unit
contribute to correction of axial chromatic aberration adjacent the
clear apertures thereof.
8. The lens of claim 1 where said negative lens element of said
front lens unit changes in optical power with height from the
optical axis of the lens to contribute to correction of axial
chromatic aberration in combination with the power of the preceding
positive element of said front lens group.
9. The lens of claim 1 where said front lens unit and said another
lens unit move in the same direction but at differential rates to
vary the focal length of said lens.
10. A projection lens for a cathode ray tube comprising from the
image end,
a first positive lens element having at least one aspheric surface
followed closely by a second negative lens element of high
dispersion having at least one aspheric surface, a third strongly
positive lens element followed by a fourth negative lens element
having at least one aspheric surface, and a fifth negative lens
unit having a strongly concave image side surface and adapted to be
closely coupled to a cathode ray tube.
11. The lens of claim 10 further including another positive lens
element closely adjacent said third lens element on the image side
of said third lens element.
12. The lens of claim 10 further including a corrector lens unit of
weak optical power having at least one aspherical surface
positioned between said fourth lens element and said fifth negative
lens unit so that the axial marginal rays from the long conjugate
side of said lens intersect said corrector lens element below the
clear aperture thereof.
13. The lens of claim 10 where the absolute value of the optical
power of said second negative lens element increases from the
optical axis to the clear aperture thereof due to said at least one
aspheric surface thereof.
14. The lens of claim 10 where said first and second lens elements
contribute to correction of axial chromatic aberration adjacent the
clear apertures thereof.
15. The lens of claim 10 where said third and fourth lens elements
contribute to correction of axial chromatic aberration adjacent the
clear apertures thereof.
16. The lens of claim 10 where said negative lens elements change
in absolute optical power with height from the axis of the lens to
the clear aperture thereof due to the aspheric surfaces on each
element.
17. A projection lens for a cathode ray tube comprising a first
positive element having at least one aspheric surface, a second
negative lens element closely spaced to said first element having
at least one aspheric surface and being of stronger absolute
optical power adjacent the clear aperture thereof than at the
optical axis, said second element having a high dispersion similar
to the dispersion of flint glass, said first lens element having a
dispersion similar to the dispersion of crown glass, a third
strongly positive lens element having a dispersion similar to the
dispersion of crown glass, a fourth negative lens element closely
spaced to said third lens element having a dispersion similar to
the dispersion of flint glass, said fourth lens element having at
least one aspheric surface which increases in absolute optical
power from the optical axis to the clear aperture thereof, and a
lens unit having a strongly concave image side surface adapted to
be closely coupled to a cathode ray tube.
18. The lens of claim 17 further including another positive lens
elements on the image side of said third lens element and closely
spaced thereto.
19. The lens of claim 17 further including a corrector lens element
of weak optical power having at least one aspheric surface
positioned between said fourth lens element and said lens unit such
that the axial marginal rays from the long conjugate side of said
lens interact said corrector lens element below the clear aperture
thereof.
20. The lens of claim 17 where said lens first and second elements
contribute to correction of axial chromatic aberration adjacent the
clear apertures thereof.
21. The lens of claim 17 where said third and fourth elements
contribute to correction of axial chromatic aberration adjacent the
clear apertures thereof.
22. The lens of claim 17 where said second and fourth negative lens
elements change in absolute optical power with height from the axis
of the lens to the clear aperture thereof due to at least one
aspheric surface on each element.
23. A projection lens for a cathode ray tube comprising from the
long conjugate side a first lens unit of weak power, including a
positive element followed by a closely spaced negative element
having at least one aspherical surface and made out of material
with higher dispersion than said positive element; a second lens
unit providing most of the positive power of the lens and including
at least one positive element followed by a closely spaced negative
element having higher dispersion than the preceding positive
element; and a third lens unit of negative power and including a
strong negative element in the vicinity of a cathode ray tube.
24. The lens of claim 23 where said second lens unit comprises two
positive elements.
25. The lens of claim 23 further including a corrector lens element
positioned between said second and said third lens units, said
corrector element having at least one aspherical surface.
26. The lens of claim 23 where the optical power of the negative
lens element in said first lens unit changes from the optical axis
to the clear aperture thereof.
27. The lens of claim 23 where the optical power of the negative
lens element in said second lens unit gradually changes from the
optical axis to the clear aperture thereof.
28. The lens of claim 23 where said positive and negative lens
elements of said first and second units contribute to correction of
axial chromatic aberration adjacent the clear aperture thereof.
29. A projection lens for a cathode ray tube comprising from the
long conjugate a first positive lens element having at least one
aspherical surface followed closely by a second negative lens
element of high dispersion having at least one aspherical surface,
a third strongly positive lens element followed by a fourth
negative lens element of high dispersion having at least one
aspherical surface, and a fifth strongly negative lens component
having a strongly concave image side surface.
30. The lens of claim 29 further including another positive lens
element closely adjacent said third lens element.
31. The lens of claim 29 further including a corrector lens element
having at least one aspherical surface positioned between said
fourth lens element and said fifth strongly negative component
adjacent to a cathode ray tube so that the axial marginal rays from
the long conjugate side of said lens intersect said corrector lens
element below the clear aperture thereof.
32. The lens of claim 29 where said negative lens elements change
in power with height from the axis of the lens to the clear
aperture thereof due to at least one aspherical surface on each
element.
33. The lens of claim 29 where said first and second elements
contribute to correction of longitudinal chromatic aberration.
34. The lens of claim 29 where said third and fourth elements
contribute to correction of longitudinal chromatic aberration.
35. A projection lens for a cathode ray tube comprising a first
positive element having at least one aspheric surface, a second
negative lens element closely spaced to said first element and
having at least one aspheric surface and being of stronger absolute
power adjacent the clear aperture thereof than at the optical axis,
said second element having a high dispersion similar to the
dispersion of flint glass, said first lens element having a
dispersion similar to the dispersion of crown glass, a third
strongly positive element with a dispersion similar to the
dispersion of crown glass, a fourth negative lens element closely
spaced to said third lens element having a dispersion similar to
the dispersion of flint glass, said fourth lens element having at
least one aspherical surface and being of stronger absolute power
adjacent the clear aperture thereof than at the optical axis, and a
fifth negative lens having a strongly concave surface facing the
long conjugate side and adapted to be closely coupled to a cathode
ray tube.
36. The lens of claim 35 further including another positive lens
element on the long conjugate side of the third lens element and
closely spaced thereto.
37. The lens of claim 35 further including a corrector lens element
having at least one aspheric surface positioned between said fourth
lens element and said fifth lens.
38. A projection lens for a cathode ray tube comprising from the
long conjugate a first unit of a weak power and including at least
one positive element of low dispersion and one negative element of
high dispersion and having at least one aspherical surface; a
second lens unit providing most of the positive power of the lens
and including at least one positive element of low dispersion and
one negative element of high dispersion, a third lens unit of
strong negative power adapted to be closely coupled to a cathode
ray tube, said lens being capable of changing magnifications by
moving said first and said second lens units along the optical axis
in a predetermined manner relative to each other while keeping said
third unit stationary relative to a cathode ray tube.
39. The lens of claim 38 further including a corrector lens unit
having at least one aspherical surface and positioned between said
second and said third lens units, said corrector lens unit being
kept stationary with respect to said third unit while said first
and second lens units are moved to change magnification.
40. The lens of claim 38 where said negative elements in said first
and second lens units change in power with height from the axis of
the lens to the clear aperture thereof to contribute to correction
of axial chromatic aberration in combination with the power of the
preceding element. .Iadd.
41. A projection lens for a cathode ray tube comprising from the
long conjugate side:
(a) a first lens unit of weak power comprising first and second
elements, the first element having a lower dispersion than the
second element and the second element having at least one aspheric
surface, said first and second elements having positive and
negative powers, respectively, at least in the vicinity of their
clear apertures which serve to correct the lens' axial chromatic
aberration;
(b) a second lens unit providing most of the positive power of the
lens comprising third and fourth elements, the third element having
a lower dispersion than the fourth element and the fourth element
having at least one aspheric surface, said third and fourth
elements having positive and negative powers, respectively, at
least in the vicinity of their clear apertures which serve to
correct the lens' axial chromatic aberration; and
(c) a third lens unit of negative power adapted to be closely
coupled to a cathode ray tube..Iaddend..Iadd.
42. A projection lens for a cathode ray tube comprising a rear lens
unit adapted to be closely coupled to a cathode ray tube at the
object end thereof, said lens unit having a strongly concave image
side surface,
a front lens unit on the image side of said lens comprising a
positive image side element having a dispersion similar to the
dispersion of crown glass followed by a closely spaced negative
element of high dispersion similar to the dispersion of flint
glass, and
another lens unit providing substantially all of the positive
optical power of said lens intermediate said front and rear lens
units, said another lens unit including a negative element of high
dispersion similar to the dispersion of flint glass on the object
side thereof,
wherein the lens further includes a corrector lens unit of weak
optical power having at least one aspherical surface positioned
between said rear lens unit and said another lens unit so that the
axial marginal rays from the long conjugate side of said lens
intersect said corrector lens unit below the clear aperture
thereof, and
said front lens unit and said another lens unit move in fixed
relation and said rear lens unit together with said corrector lens
unit moved in fixed relation but differentially with respect to
said front lens unit and said another lens unit to vary the focal
length of said lens..Iaddend..Iadd.43. A projection lens for a
cathode ray tube comprising a rear lens unit adapted to be closely
coupled to a cathode ray tube at the object end thereof, said lens
unit having a strongly concave image side surface,
a front lens unit on the image side of said lens comprising a
positive image side element having a dispersion similar to the
dispersion of crown glass followed by a closely spaced negative
element of high dispersion similar to the dispersion of flint
glass, and
another lens unit providing substantially all of the positive
optical power of said lens intermediate said front and rear lens
units, said another lens unit including a negative element of high
dispersion similar to the dispersion of flint glass on the object
side thereof,
wherein the absolute value of the optical power of said negative
lens element of said front lens unit increases from the optical
axis to the clear aperture thereof due to at least one aspheric
surface thereof..Iaddend..Iadd.44. A projection lens for a cathode
ray tube comprising a rear lens unit adapted to be closely coupled
to a cathode ray tube at the object end thereof, said lens unit
having a strongly concave image side surface,
a front lens unit on the image side of said lens comprising a
positive image side element having a dispersion similar to the
dispersion of crown glass followed by a closely spaced negative
element of high dispersion similar to the dispersion of flint
glass, and
another lens unit providing substantially all of the positive
optical power of said lens intermediate said front and rear lens
units, said another lens unit including a negative element of high
dispersion similar to the dispersion of flint glass on the object
side thereof,
wherein said negative lens element of said front lens unit changes
in optical power with height from the optical axis of the lens to
contribute to correction of axial chromatic aberration in
combination with the power of the preceding positive element of
said front lens
unit..Iaddend..Iadd. . A projection lens for a cathode ray tube
comprising a rear lens unit adapted to be closely coupled to a
cathode ray tube at the object end thereof, said lens unit having a
strongly concave image side surface,
a front lens unit on the image side of said lens comprising a
positive image side element having a dispersion similar to the
dispersion of crown glass followed by a closely spaced negative
element of high dispersion similar to the dispersion of flint
glass, and
another lens unit providing substantially all of the positive
optical power of said lens intermediate said front and rear lens
units, said another lens unit including a negative element of high
dispersion similar to the dispersion of flint glass on the object
side thereof,
wherein said front lens unit and said another lens unit move in the
same direction but at differential rates to vary the focal length
of said lens..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to projection lenses for cathode ray tubes
and, more particularly, relates to such lenses which are color
corrected.
BACKGROUND OF THE INVENTION
In projection television systems it is a common practice to utilize
three cathode ray tubes (CRT) of different colors, namely, red,
blue and green. The images formed on each of these CRT's is
projected onto a screen where the three separate images are
combined to form a full color picture. Lenses used in this
application can be generally characterized by a construction which
includes a strong negative element in the vicinity of the CRT, a
strong positive power component at some distance away from said
negative element, and a weaker component furthest away from the
CRT. Examples of such lenses are shown in U.S. Pat. Nos. 4,300,817;
4,348,081 and 4,526,442.
In practice, the phosphors used in CRT's do not emit strictly
monochromatic light. The emission spectrum of the green CRT, in
particular, has significant side bands in red and blue parts of the
spectrum. If projection lenses are not corrected for color, this
chromatic spread will result in a lower overall image contrast and
in sometimes visible color fringing. Therefore, to achieve the
image quality requirements of high end projectors, including data
display, intermediate definition and high definition television
(IDTV and HDTV) applications, it is desirable to provide some
degree of correction for chromatic aberrations in the lens.
Examples of partially color corrected lenses are disclosed in U.S.
Pat. Nos. 4,530,575; 4,733,953, 4,758,074; 4,778,264 and 4,815,831.
Fully color corrected lenses for data display and high definition
TV applications are shown in U.S. Pat. Nos. 4,767,199 and
4,792,218.
The requirement for partial or total color correction always
complicates an optical design problem. To achieve some degree of
control of chromatic aberrations a combination of elements of
various dispersions and powers must be used. That, in turn, makes
it more difficult to correct for monochromatic aberrations like
spherical, coma, astigmatism, etc. In the end, a color corrected
lens become more complex, with a larger number of elements, and is
more expensive to manufacture than the lens with only monochromatic
aberration correction. An increased number of elements also leads
to higher losses in transmission and contrast. And, since the
individual elements in these lenses are quite large in size,
additional increases in weight of these lenses become
significant.
Additionally, it is often desirable that lenses be capable of high
performance levels over a significant range of magnifications.
Ideally, in front projection application the same lens might be
used over a range of magnifications from 10.times. to 60.times.
without any degradation in image quality. This further complicates
the optical design.
Focusing very fast f/1.0 lenses covering a wide field of view has
always been difficult. It is desirable to be able to use the same
lens. For example, the same front projector should be easily
adaptable to various size auditoriums by simply refocusing the
projection lenses without any loss in image quality, or the lens
used on one model of the rear projector should be also usable on a
wide variety of other models and sizes of rear projection TV sets
when appropriately refocused.
The most common way of focusing projection TV lenses usually
involves moving the whole lens along the optical axis. When the
rear strong negative element is liquid coupled to the CRT, only the
front portion of the lens is moved. This focusing technique works
sufficiently well over a limited range of magnifications.
Variations of spherical aberrations and astigmatism usually prevent
the range to be extended substantially. When conjugates are changed
significantly the lens must be partially or completely
redesigned.
Accordingly, the present invention provides new and improved color
corrected projection lenses for CRT's of high definition while
maintaining a wide field of view and a large relative aperture. The
invention also provides a CRT projection lens that is capable of
maintaining a high level of image quality over a wide range of
magnifications. The invention also provides a lens which achieves a
good image and a high degree of stability of aberrations correction
with shift of conjugates in a relatively simple configuration.
SUMMARY OF THE INVENTION
Briefly stated, the invention in one form thereof comprises a
projection lens which includes from the long conjugate a first unit
of two elements, one positive and one negative, having a weak
combined power, a second lens unit providing most of the positive
power of the lens and including at least one positive element
followed by a negative element, and a third unit which includes a
strong negative element in the vicinity of the CRT. Each of the
negative elements in the first and the second units have at least
one aspherical surface.
The longitudinal chromatic aberration or axial color is corrected
by an appropriate combination of positive and negative elements
with different dispersion characteristics. The better the
correction, the stronger the powers of a positive and a negative
elements must be, or the dispersion difference between these
elements must be increased. By using two negative elements instead
of one the power of each of these negative elements can be kept
weak, with each of the first and the second units partially
correcting for axial color. Any transverse blur in the image plane
caused by the axial color is proportional to the square of the
height of the axial marginal ray. The size of this aberration at
smaller aperture heights is not significant enough to effect the
performance of the lens. Only when the aperture becomes larger
especially for f/1.0 lenses, does this aberration become important
to correct. Therefore, aspherical surfaces can be used to shape the
negative elements in such a way so that the correction of axial
color is accomplished mainly for outlying portions of the aperture,
that is, in the areas closer to the maximum clear apertures of the
elements of the first and the second units of the lens.
Consequently, the refractive power of these negative elements,
while relatively weak on axis, gradually increases towards the
outer portion of the elements. If the surfaces of these elements
were spherical with corresponding base radii, the refractive power
of the elements would not change across the diameter, and the
correction of color would only be partial, and not sufficient to
achieve a high performance level. If, however, the radii of these
elements were made short enough to obtain an appropriate correction
of chromatic aberrations, then additional elements would be needed
to obtain an adequate correction of monochromatic aberrations and,
also, satisfy the basic physical specifications of the lens such as
focal length, field of view and relative aperture.
Having negative elements of relatively weak power also helps to
keep the variation of thickness across the diameter of the element
reasonably small, thus allowing for economical manufacture of these
elements by molding them from out of an appropriate plastic
material.
When the field of view of the lens is increased and the optical
performance requirements are raised to higher levels, it is helpful
to add another element between the second and third lens units.
Placing an element with at least one aspherical surface in that
location allows for better correction of sagittal oblique spherical
aberrations and other residual offaxis aberrations.
A new focusing method involves moving the first and the second lens
units along the optical axis in a predetermined fashion relative to
each other. The third lens unit and a corrector, if any, remain
fixed relative to the CRT. The motion of the first two units can be
controlled by a cam or a double helocoid to achieve a simultaneous
change in position of these two units. By focusing a lens in this
fashion a very stable high quality optical performance can be
achieved with a minimum number of elements.
In a preferred embodiment the strongest positive elements in the
second lens unit are made out of glass to achieve some thermal
stability, as described in the prior art. The rest of the elements
are plastic. This allows for the most economical manufacturing of
the aspherical elements. Because some of the plastic elements have
positive power and some have negative power, and their thermo optic
coefficients describing the change in the refractive index as a
function of temperature are similar, it is also possible to improve
the thermal stability of the lens even further by choosing
appropriate powers for these elements.
An object of this invention is to provide a new an improved color
corrected lens which has a fast relative aperture, covers a wide
field of view and is simple and inexpensive to manufacture in large
quantities.
Another object of this invention is to provide a novel focusing
method for a projection TV lens which allows for the lens to
achieve a great stability of image quality over a large range of
magnifications.
The features of the invention which are believed to be novel are
particularly pointed out and distinctly claimed in the concluding
portion of this specification. The invention, however, together
with further objects and advantages thereof may best be appreciated
by reference to the following detailed description taken in
conjunction with the drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1, 2, 3 and 4 are schematic side elevations of lenses
embodying the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
A first lens embodying the invention as illustrated in FIG. 1
comprises a first or front lens unit G1 comprised of elements L1
and L2. Lens element L1 is positive and is of a low dispersion
material, similar to crown glass, such as acrylic and has at least
one aspheric surface. Element L1 in lens unit G1 is closely
followed by a negative lens element L2 having high dispersion
characteristic of flint glass. The optical power at the axis of
lens element L2 is very low as will hereinafter be made apparent,
lens element L2 has at least one aspheric surface which changes in
power towards the clear aperture thereof to provide correction for
axial chromatic aberration. Lens element L1 also has an aspheric
surface which changes in power towards the clear aperture thereof.
The elements L1 and L2 cooperate in powers and dispersion in the
vicinities of the clear apertures thereof to contribute to
correction of axial chromatic aberration.
A second or another lens unit G2 comprises the major power element
L3 of the lens of a material similar to crown type glass followed
by a negative lens element L4 of high dispersion which is closely
spaced thereto and in which the axial marginal rays AM intersect
the lens at a height very close to the clear aperture to provide
further correction for axial chromatic aberration.
A third or rear lens unit G3 comprises a lens element L5 and a
housing member identified by the reference numeral L6 which
contains a liquid coolant which is of a compatible index of
refraction to lens element L5. The element L6 not only provides
negative optical power to contribute to correction of field
curvature but provides a coolant for the cathode ray tube C.
It will be noted that the axial marginal rays as denoted by the
reference numeral AM intersect the elements L2 and L4 very close to
the clear aperture thereof to provide correction for axial
chromatic aberration.
In the lenses described the elements L2 and L4 (FIGS. 1, 2 and 4)
and elements L2 and L5 (FIG. 3) are configured in the vicinity of
the clear aperture to contribute to correction of axial color by
the provision of at least one aspheric surface which changes the
power of the elements in the vicinity of the clear apertures
thereof with respect to the paraxial power.
A lens as shown in FIG. 1 is substantially described in Table
I.
A lens embodying the invention, as shown in FIG. 2, is somewhat
similar to the lens of FIG. 1 but it includes a corrector lens unit
CT between the second lens unit G2 and lens unit G3. The lens shown
in FIG. 2 comprises a lens unit G1 having a positive lens L1 and a
negative lens L2 of much higher dispersion as measured by its Abbe
number. Lens unit G2 comprises a optically strong unit L3 followed
by a negative unit L4 having a very high dispersion providing color
correction for axial chromatic aberrations adjacent the clear
aperture thereof. Lens G2 is followed by a strongly concave
negative lens unit G3 which comprises what may be considered a
shell element L6 followed by an element which includes a liquid
coupler L7 of appropriate refractive index between element L6 and a
cathode ray tube. The cathode ray tube is curved on the phosphor
side thereof to provide some optical power. In this regard since
the interior surface of the CRT contributes optical power, it is
included in the prescription in Table II for the lens shown in FIG.
2.
In the lens embodiments of FIGS. 1 and 2, the lens element L4 may
be considered part of lens unit G2 inasmuch as in contributing to
correction of axial chromatic color aberration it cooperates with
element L3. It will be noted that the axial marginal rays AM in the
embodiment shown in FIG. 2 strike the element L4 closely adjacent
the clear aperture thereof where it is of strongest power and
together with the preceding positive element contributes to
correction of axial chromatic aberration. The axial marginal rays
as shown in FIG. 2 strike the corrector element CT at slightly less
than the clear aperture thereof so as to help to contribute to
aperture dependent aberrations but leave some room at the outer
edges thereof to contribute to correction of off axis aberrations
such as sagittal oblique spherical aberrations.
A lens as shown in FIG. 2 is substantially described in Table
II.
The lens of FIG. 3 is primarily designed for front projection and
has a longer equivalent focal length as set forth in Table III. The
lens of FIG. 3 comprises a first lens unit G1 which comprises a
positive element followed by a closely spaced negative element of
very high dispersion to contribute correction of axial chromatic
aberration particularly at the outer edges thereof. The second lens
unit G2 comprises two positive elements L3 and L4 followed by a
negative lens unit L5 which also provides at its outer edges
thereof in conjunction with element L4 correction for axial
chromatic aberration. Element L5 has at least one aspheric surface,
and the absolute power of the lens increases from the axis thereof
toward the clear aperture due to this aspheric surface.
The third lens unit G3 comprises an element L7 which is closely
coupled to a cathode ray tube C. In this embodiment there is an
X-Ray absorbing plate P and in between a housing H which holds a
cooling liquid between the cathode ray tube C and the X-Ray
absorbing plate P.
Additionally, a corrector lens unit CT having at least one aspheric
surface is positioned between the second lens unit G2 the third
lens unit G3.
This corrector lens unit aids in correction of aperture dependent
aberrations towards the central area thereof while providing
correction for off axis aberration at the outer edges thereof.
The embodiment of FIG. 3 may be considered to be air coupled to the
CRT while the embodiments of FIGS. 1 and 2 are optically coupled to
the CRT in view of the liquid containing housing units designated
by the lens L6 in FIG. 1 and L7 in FIG. 2.
A lens as shown in FIG. 3 is substantially described in Table
III.
Lenses as shown in FIG. 4 have a similar configuration to the lens
of FIG. 2, but are adapted for a large range of magnifications as
well hereinafter be described.
Two lenses as shown in FIG. 4 are substantially described in Tables
IV and V.
In the lens of FIG. 1, at least one surface of element L1 as well
as the difference in dispersion of the cooperating positive element
is configured to cooperate with element L2 in the vicinity of the
clear aperture to contribute to correction of axial chromatic
aberration. This is also true in all other examples.
Axial longitudinal chromatic aberration adjacent the clear aperture
of the lens elements is corrected by the combination of the
positive and negative elements of the lens units G1 and also the
positive and negative elements of the lens unit G2.
It will depend upon the decision of the TV manufacturer as to
whether it wishes to have an optically coupled lens as shown in
FIGS. 1, 2 and 4 or an air coupled lens as shown in FIG. 3.
In the disclosed embodiment of the invention, lens elements have
aspheric surfaces defined by the equation ##EQU1## where x is the
surface sag at a semi-aperture distance y from the axis A for the
lens, C is the curvature of the lens surface at the optical axis, K
is a conic constant, and D, E, F, G, H and I are aspheric
coefficients of correspondingly fourth through fourteenth order in
even expotential powers.
In the following tables, the lens elements are identified from the
image end to object end by the reference L followed by successive
Arabic numerals. Lens surfaces are identified by the reference S
followed by successive Arabic numerals from the image to the object
end. Positive radii are struck from the right and negative radii
from the left. The index of refraction of each element is given
under the heading Ne. The dispersion of each lens element as
measured by its Abbe number is given by Ve.
The index of refraction given by the symbol Ne represents the green
mercury line and the dispersion Ve is also to the green mercury
line. Other parameters of disclosed lenses embodying the invention
are also set forth in Tables I-V, and the following tables.
TABLE I
__________________________________________________________________________
SURFACE RADIUS AXIAL DISTANCE LENS (mm) BETWEEN SURFACES (mm)
N.sub.e V.sub.e
__________________________________________________________________________
S1 79.7613 L1 20.0000 1.49354 57.34 S2 -669.9136 4.6902 S3
-116.8472 L2 7.0000 1.59495 30.70 S4 1056.4020 23.6442 S5 70.9138
L3 28.0000 1.64128 55.19 S6 -124.5127 .5000 S7 -105.1656 L4 8.2300
1.59495 30.70 S8 -269.9804 55.3717 S9 -59.4288 L5 3.7500 1.49354
57.34 S10 -58.0000 L6 8.0000 1.42900 50.00 S11 plano L7 5.7500
1.53700 50.00 S12 plano -.0002
__________________________________________________________________________
ASPHERICAL SURFACE DATA: S D E F G H I
__________________________________________________________________________
S1 -.42555E-06 -.49543E-09 .26480E-12 -.20345E-15 .61635E-19
-.12486E-22 S2 -.52887E-06 -.23095E-09 .60365E-13 .66225E-16
-.54544E-19 .11586E-22 S4 -.22688E-07 .18679E-10 -.52303E-13
-.20711E-16 .90800E-20 -.15468E-23 S7 -.20618E-06 .78774E-09
-.42344E-12 .11201E-15 -.24723E-19 .39342E-23 S8 .77243E-06
.68520E-09 -.21054E-13 -.15621E-15 .54388E-19 -.70704E-23 S9
-.19224E-05 .10054E-09 -.51595E-13 .70329E-16 .51214E-19
-.42912E-22
__________________________________________________________________________
EFL = 99.0 mm f/NO = 1.10 as infinity
TABLE II
__________________________________________________________________________
SURFACE RADIUS AXIAL DISTANCE LENS (mm) BETWEEN SURFACES (mm)
N.sub.e V.sub.e
__________________________________________________________________________
S1 74.2416 L1 17.5000 1.49354 57.34 S2 1890.7290 6.3993 S3
-353.7105 L2 6.0000 1.59495 30.70 S4 168.5545 7.9750 S5 76.7012 L3
29.5000 1.59142 61.03 S6 -102.6833 .4500 S7 -140.5109 L4 6.0000
1.59495 30.70 S8 2405.5770 1.8204 S9 3614.1540 L5 13.0000 1.49354
57.34 S10 -107.5106 Z1 S11 -54.2507 L6 5.0000 1.49354 57.34 L7
5.0000 1.43300 50.00 S13 plano L8 13.1000 1.56600 50.00 S14
-350.0000 -.0007
__________________________________________________________________________
ASPHERICAL SURFACE DATA: S D E F G H I
__________________________________________________________________________
S1 -.30278E-06 -.39696E-09 .65578E-12 -.54355E-15 .22972E-18
-45485E-22 S2 .50238E-06 .29645E-09 -.19419E-12 .15207E-15
-.14647E-18 .35404E-22 S3 .33721E-06 -.11255E-09 -.67345E-13
-.23116E-16 -.57597E-20 .59609E-23 S4 .45051E-06 -.39788E-11
.15672E-12 .44925E-16 .36143E-19 -.11782E-22 S7 -.17777E-06
.14069E-08 -.77347E-12 .29025E-15 -.69186E-19 .35744E-23 S8
.13689E-05 .13175E-08 -.50402E-12 -.19391E-15 .35271E-18
-.53285E-22 S9 .16754E-05 -.39851E-09 .28977E-12 -.29520E-15
.20386E-18 .44467E-22 S10 .33475E-06 -.16086E-09 .11848E-12
-.60788E-16 -.66995E-19 .82337E-22 S11 .61205E-05 .53626E-08
-.35544E-11 .63970E-15 .29820E-18 -10191E-21
__________________________________________________________________________
EFL = 89.4 mm f/NO = 1.0 at infinity
TABLE III
__________________________________________________________________________
SURFACE RADIUS AXIAL DISTANCE LENS (mm) BETWEEN SURFACES (mm)
N.sub.e V.sub.e
__________________________________________________________________________
S1 118.0413 L1 19.0000 1.49354 57.34 S2 279.5864 20.1020 S3
-270.8739 L2 9.0000 1.59495 30.70 S4 270.8739 14.9593 S5 171.0173
L3 40.5796 1.51872 64.02 S6 -171.0173 .2000 S7 83.7713 L4 35.6330
1.51872 64.02 S8 -1328.3410 9.9750 S9 2057.5210 L5 8.0000 1.59495
30.70 S10 85.7104 Z1 S11 257.6417 L6 19.0000 1.49354 57.34 S12
-178.9754 25.2767 S13 -69.6645 L7 5.0000 1.49354 57.34 S14 466.9425
Z2 S15 plano L8 6.5000 1.53700 50.00 S16 plano L9 4.8100 1.42000
50.00 L10 5.7500 1.57200 50.00 S18 plano .0024
__________________________________________________________________________
ASPHERICAL SURFACE DATA: S D E F G H I
__________________________________________________________________________
S1 -.11621E-06 -.49544E-10 .18681E-13 -.67047E-17 .11303E-20
-.69308E-25 S2 .38060E-08 -.62373E-11 -.25648E-14 .27436E-17
-.54489E-21 .69514E-25 S3 -.32858E-07 -.47960E-11 -.16998E-15
.21168E-18 .19367E-22 -.78372E-26 S4 .32858E-07 .47960E-11
.16998E-15 -.21168E-18 -.19367E-22 .78372E-26 S9 -.18988E-06
.79851E-10 -.28921E-13 .54158E-17 -.50610E-21 -72986E-27 S10
.11973E-06 .15072E-09 -.23489E-13 .81292E-17 .23668E-20 -.55905E-24
S11 51476E-07 .13917E-10 -.21354E-13 .96526E-18 24004E-20
-.85472E-24 S12 .30763E-06 -.82701E-10 -.79401E-14 .40372E-17
-.55063E-22 -.11513E-23 S13 .16025E-06 -.33837E-09 .82317E-13
.33406E-16 -.16682E-19 .23473E-24 S14 -.47493E-06 -.77318E-10
.29802E-13 -.57967E-17 .25949E-21 -.40005E-25
__________________________________________________________________________
EFL = 139.4 mm f/No = 1.0 at infinity
In the .[.following.]. .Iadd.foregoing .Iaddend.Tables I-III the
conic constant K is 1.3258.
TABLE IV
__________________________________________________________________________
SURFACE RADIUS AXIAL DISTANCE LENS (mm) BETWEEN SURFACES (mm)
N.sub.e V.sub.e
__________________________________________________________________________
S1 93.9194 L1 33.5000 1.49354 57.34 S2 658.9023 3.5151 S3 -548.1886
L2 9.0000 1.59495 30.70 S4 287.3305 Z1 S5 93.2579 L3 31.0000
1.64128 55.19 S6 -267.6059 .2000 S7 418.1418 L4 8.0000 1.59495
30.70 S8 93.2263 Z2 S9 158.2390 L5 18.0000 1.49354 57.34 S10
-1011.3090 40.8304 S11 -59.1138 L6 5.0000 1.49354 57.34 S12
-66.5000 L7 7.0000 1.43900 55.00 S13 plano L8 10.3000 1.53700 50.00
S14 plano -.0004
__________________________________________________________________________
ASPHERICAL SURFACE DATA: S D E F G H I
__________________________________________________________________________
S2 -.23232E-06 .42953E-11 .22237E-14 .28556E-17 -.10121E-20
.55278E-25 S3 .29504E-07 .85467E-11 .52630E-15 -.51414E-18
-.11801E-21 -.28899E-26 S4 .43027E-06 .29611E-10 .28426E-14
-.27848E-17 .33655E-21 .24211E-25 S7 -.16002E-06 .92877E-10
-.36095E-13 .55299E-17 -.40886E-21 -.49637E-25 S8 .12375E-06
.17993E-09 -.43680E-13 .72048E-17 .38525E-20 -.90356E-24 S9
.21084E-06 -.50871E-10 .26661E-13 -.88729E-17 .10243E-20 .16196E-25
S10 .66547E-07 .76684E-12 -.33818E-13 .34535E-17 .92518E-21
-.30429E-24 S11 -.20945E-06 -.10691E-09 .16506E-12 .83919E-18
-.23434E-19 .57245E-23
__________________________________________________________________________
TABLE V
__________________________________________________________________________
SURFACE RADIUS AXIAL DISTANCE LENS (mm) BETWEEN SURFACES (mm)
N.sub.e V.sub.e
__________________________________________________________________________
S1 79.2080 L1 26.0000 1.49354 57.34 S2 620.7167 6.2518 S3 -187.0779
L2 8.0000 1.59495 30.70 S4 863.5535 Z1 S5 87.2949 L3 25.5000
1.64128 55.19 S6 -198.4495 .2000 S7 864.7596 L4 8.0000 1.59495
30.70 S8 100.0126 Z2 S9 164.8389 L5 14.0000 1.49354 57.34 S10
-543.7059 43.8086 S11 -53.9053 L6 4.0000 1.49354 57.34 S12 -61.0000
L7 8.7000 1.43900 55.00 S13 L8 6.5000 1.53900 59.00 S14 -.0003
__________________________________________________________________________
ASPHERICAL SURFACE DATA: S D E F G H I
__________________________________________________________________________
S1 .37138E-07 -.26219E-10 .23371E-13 -.40549E-17 -.57581E-21
.37161E-24 S2 -.28674E-06 .30963E-10 .14473E-13 .16963E-16
-.84215E-20 .36035E-24 S3 .42304E-06 .66225E-10 -.89951E-14
-.61368E-17 -.12988E-20 14200E-24 S4 .10031E-05 .83141E-10
.28007E-13 -.20575E-16 .44543E-20 .27305E-23 S7 -.63512E-07
.15646E-09 -.87382E-13 .30696E-16 -.93757E-20 .11178E-23 S8
.31335E-06 .25228E-09 -.77793E-13 .41139E-16 -.99160E-20 .16425E-23
S9 .23544E-06 -.11740E-09 .53503E-13 -.34734E-16 .26122E-21
.45851E-23 S10 .15690E-06 -.11252E-09 .26590E-13 -.27785E-16
-.65235E-20 .71119E-23 S11 -.11893E-05 .58553E-09 .29907E-13
-.25989E-16 -.22814E-19 .13396E-22
__________________________________________________________________________
The conic constant K in Tables IV and V is zero.
The following Table VI is set forth, for purposes of example only,
to show the change in power of the high dispersion negative
elements and the change in power due to aspheric surfaces adjacent
to or in the vicinity of the clear aperture to contribute to
correction of axial chromatic aberration.
In Table VI the quantity K.sub.A is the ratio of the power of the
element at the optical axis of the lens to the power of the overall
lens. The quantity K.sub.C is the ratio of the power of the lens
element at the clear aperture to the power of the overall lens. The
power of the lenses of Tables III-IV is at the shortest EFL.
It will be noted that in the examples of Tables II-V the power
increases substantially from the optical axis denoted as K.sub.A to
the clear aperture K.sub.C. In the example of FIG. 1 and Table I,
the first element L1 goes from positive power at the optical axis A
to lesser power at the clear aperture, while the second element L2
changes in power to a lesser value.
The power of a lens at any height from the optical axis, is
calculated by the equation: ##EQU2## where K is the power of the
element at the optical axis or at a given height from the optical
axis;
n is the index of refraction;
C.sub.1 is the local curvature of one surface of the lens element
at a given height;
C.sub.2 is the curvature of the other surface of the lens element
at the same given height, and
t is the axial thickness of the lens element.
TABLE VI ______________________________________ L1 L2 L4 L5
______________________________________ Table I .755 -.562 -.339
K.sub.A K.sub.C .667 -.249 -1.636 Table II K.sub.A .573 -.466 -.399
K.sub.C 2.386 -3.556 -2.827 Table III K.sub.A .35 -.615 -.926
K.sub.C .38 -1.488 -2.061 Table IV K.sub.A .634 -.437 -.679 K.sub.C
2.253 -5.464 -1.833 Table V K.sub.A .628 -.442 -.596 K.sub.C 1.467
-3.469 -1.503 ______________________________________
The correction of axial chromatic aberration through the use of a
combination of positive or negative components can be obtained in
accordance with the following relationship. ##EQU3## where K.sub.1
and K.sub.2 are the powers of the elements L1 and L2 respectively,
V.sub.1 and V.sub.2 are the dispersions of elements L1 and L2
respectively, K is the combined power of elements L1 and L2, and V
is the effective Abbe value of the combined elements.
For complete correction of axial chromatic aberration V is infinity
and ##EQU4##
The foregoing exemplifies the considerations of the powers and
dispersions of cooperating positive and negative elements.
In the examples of Tables II-V, the power of the positive element
L1 of the first lens unit G1 increases toward the clear aperture,
while the negative power of element L2 increases in absolute value,
both increases due to the aspheric surfaces thereof.
In the second lens units G2 of all examples only the negative
element changes in power from the optical axis to the clear
aperture due to aspheric surfaces, since the positive elements of
lens unit G2 are spherical. However, if desired an aspheric
surfaces(s) could be provided on a power element L3 (or L4 in Table
III).
In all embodiments the negative element of a positive negative
combination changes in power in such a way from the optical axis to
the clear aperture with respect to the power of the preceding
positive element(s) to contribute to obtaining a favorable
correction of axial chromatic aberration in the vicinity of the
clear aperture.
As will be seen from FIG. 1 and Table I, this relationship may be
satisfied by making element L1 go less positive adjacent the clear
aperture and consequently L2 goes less negative. The elements L1
and L2 are plastic and may economically have aspheric surface(s)
defined thereon to achieve this effect.
In the examples in Tables II-V contribution to axial color
correction is achieved primarily by aspheric surfaces on the
cooperating high dispersion negative elements L4 which increase in
negative power with aperture height, in conjunction with the
corresponding power of the proceeding positive element.
In all examples contribution to correction of axial chromatic
aberration is also made by the combination of the power of elements
and the following negative element L4 (L5 in Table III) through
high dispersion and related power in regard to the proceeding
positive power element(s) in the vicinity of the clear
apertures.
What is stated for the values of K/V with regard to FIG. 1 and
Table I is equally valid with respect to the other examples, as
well as the cooperating positive and negative elements of lens unit
G2 of all examples.
A lens as shown in FIG. 3 will provide an image quality of up to
ten cycles/mm (MTF) at an image height of almost two hundred
seventy inches at a substantially same throw distance. This lens is
designed for front projection and gives excellent image quality for
data display and large magnifications. This lens is designed to be
focused by movement of L1-L5, and L6, L7 deferentially for throw
distances of approximately six and one-half feet to twenty-two and
one-half feet while maintaining good image quality. The EFL of the
lens may vary with focusing from 139.4 mm to 140.9 mm.
The focusing travel of the focusing lens units in FIG. 3 is set
forth in the following Table VII.
TABLE VII ______________________________________ EFL (mm) Z1 (mm)
Z2 (mm) ______________________________________ 140.2 19.81 4.16
140.9 17.44 3.00 139.4 22.71 5.99
______________________________________
As will be seen from the foregoing data, lens units G1 and G2 move
in fixed relation while elements L6, L7 move in fixed relation, but
differentially with respect to lens units G1 and G2.
The lens of FIGS. 1 and 2 are designed for back projection TV sets
and may be variable in focus by positioning lens units G1 and G2
with respect to lens unit G3 dependent upon the specifications of
TV manufacturers for the size of the viewing screen. The lenses of
FIGS. 1 and 2 and Tables I and II respectively, are designed for
and give good optical performance out to five cycles/mm (MTF).
The lenses of FIG. 4 and Tables IV and V are designed for variable
focusing and permit lens units G1 and G2 to differentially move to
achieve variable focusing. Table VIII sets forth the movements of
the lens units G1 and G2 for various EFL's and magnifications
M.
TABLE VIII ______________________________________ Table IV EFL (mm)
Z1 (mm) Z2 (mm) M ______________________________________ 138.0
26.25 28.88 -.076 140.4 29.10 22.56 -.044 142.3 31.37 17.93 -.021
______________________________________ Table V EFL (mm) F1 (mm) F2
(mm) M ______________________________________ 113.8 18.98 22.09
-.122 114.9 20.50 19.04 -.104 117.8 24.81 10.79 -.056
______________________________________
The lens of Table IV provides an excellent MTF out to twelve cycles
per millimeter and the lens of Table IV provides an excellent MTF
of ten cycles per millimeter at focus. Both are well balanced in
aberration correction, both monochromatic as well as chromatic.
The powers of the lens units as a ratio to the power of the overall
lens are set forth in the following Table IX:
TABLE IX ______________________________________ K.sub.1 /K.sub.0
K.sub.2 /K.sub.0 K.sub.3 /K.sub.0 T/fo
______________________________________ Table I .185 1.030 -.708
.239 Table II .168 .79 -.543 .089 Table III -.198 1.205 -.878 .107
Table IV .267 1.212 -1.145 .187 Table V .255 .676 -.946 .165
______________________________________
where K.sub.1, K.sub.2, K.sub.3 are the powers of lens units G1, G2
and G3, respectively, and K.sub.0 is the power of the overall lens,
f.sub.0 is the focal length of the lens and T is the spacing
between lens units G1 and G2.
The first lens unit G1 is of small optical power and may be either
positive or negative. The spacing T/fo is less than 0.4.
It may thus be seen that the objects of the invention set forth, as
well as those made apparent from the foregoing description, are
efficiently attained. While preferred embodiments of the invention
have been set forth for purposes of disclosure, modification to the
disclosed embodiments of the invention, as well as other
embodiments thereof, may occur to those skilled in the art.
Accordingly, the appended claims are intended to cover all
embodiments of the invention and modifications to the disclosed
embodiments which do not depart from the spirit and scope of the
invention.
* * * * *