Two position variable focal length lens

A two position variable focal length lens is provided. The variable focal length lens includes a common lens element moveably positioned on an optical axis; a wide angle lens element moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element; and a telephoto lens element moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element. A magnification ratio change is effected by moving the common lens element along the optical axis and switching between the wide angle lens element located at the first position on the optical axis and the telephoto lens element located at the second position on the optical axis.

FIELD OF THE INVENTION

This invention relates generally to lens design, and in particular to a variable focal length lens for use in a camera.

BACKGROUND OF THE INVENTION

Zoom lens system in which the rear or image side lens units switch out of and into an optical path are known. For example, U.S. Pat. No. 4,871,238, which issued to Sato et al., on Oct. 3, 1989, discloses a photographic optical device including a master lens unit having a positive refractive power; a first auxiliary lens unit having a positive refractive power capable of being placed on and off the optical path; and a second auxiliary lens unit having a negative refiactive power capable of being placed on and off the optical path. The first auxiliary lens unit is attached to an image-plane side of the master lens unit to form a photographic unit giving a low ratio of magnification. The second auxiliary lens unit is attached to an image-plane side of the master lens unit to form another photographic unit giving a high ratio of magnification. The first and second auxiliary lens units are placed outside of the optical path to form another photographic unit giving a middle ratio of magnification. The zoom lens system disclosed in U.S. Pat. No. 4,871,238 is disadvantaged in that each lens unit requires many individual lens components which increases manufacturing costs associated with building the zoom lens system and increases the complexity of the design of the zoom lens system. Additionally, the zoom lens system disclosed in U.S. Pat. No. 4,871,238 includes a wide angle, mid- range, and telephoto format (lens position) which increases the cost and complexity associated with the lens driving mechanism.

Lens systems having a reduced number of individual lens components are also known. For example, U.S. Pat. No. 5,677,798, which issued to Hirano et al., on Oct. 14, 1997, discloses an image forming lens system including a positive front lens group, a diaphragm, and a rear lens group, in order from an object to be imaged. The front lens group is made of optical glass. The rear lens group is made of a single meniscus plastic lens having opposed aspheric lens surfaces with a concave surface adjacent to the diaphragm. Additionally, U.S. Pat. No. 5,067,803, which issued to Ohno, on Nov. 26, 1991, discloses a photographic wide angle lens which is composed of, from an object side thereof, a first lens of positive meniscus having a convex surface on the object side, and a second lens of positive meniscus having a concave surface on the object side. The wide angle lens has an aspheric surface at least on one of the four lens surfaces provided by the first and second lenses. While the lens systems disclosed in U.S. Pat. Nos. 5,677,798 and 5,067,803 have a reduced number of individual lens elements, each lens system is disadvantaged in that the ratio of magnification of the lens system can not be changed.

Recent surveys of picture taking consumers using a zoom lens indicated that over 90% of all photographs are shot in either a wide angle format or a telephoto format. As such, there is a need for a variable focal length lens system having a reduced number of individual lens components capable of switching between a wide angle format and a telephoto format.

SUMMARY OF THE INVENTION

According to one feature of the present invention, a two position variable focal length lens includes a common lens element moveably positioned on an optical axis. A wide angle lens element is moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element. A telephoto lens element is moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element. A magnification ratio change is effected by moving the common lens element along the optical axis and switching between the wide angle lens element located at the first position on the optical axis and the telephoto lens element located at the second position on the optical axis. The two position variable focal length lens satisfies the following condition: |C−fZT|<|−fZW, where fCis a focal length of the common lens element, fZTis a focal length of the two position variable focal length lens in a telephoto position, and fZWis a focal length of the two position variable focal length lens in a wide angle position.

According to another feature of the present invention, a two position variable focal length lens includes a common lens element moveably positioned on an optical axis. The common lens element has an image side surface with the image side surface having a curvature. The common lens element satisfies the following condition: (1/−20.8)≦c≦(1/5), where c is the curvature of the image side surface. A wide angle lens element is moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element. A telephoto lens element is moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element. A magnification ratio change is effected by moving the common lens element along the optical axis and switching between the wide angle lens element located at the first position on the optical axis and the telephoto lens element located at the second position on the optical axis.

According to another feature of the present invention, a two position variable focal length lens includes a common lens element moveably positioned on an optical axis. A wide angle lens element is moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element. A first aperture stop is moveably positioned with the wide angle lens element on an object side of the wide angle lens element. A telephoto lens element is moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element. A second aperture stop is moveably positioned with the telephoto lens element on an object side of the telephoto lens element. A magnification ratio change is effected by moving the common lens element along the optical axis and switching between the first aperture stop and the wide angle lens element located at the first position on the optical axis and the second aperture stop and the telephoto lens element located at the second position on the optical axis such that a distance between the common lens element and the first aperture stop is equivalent to a distance between the common lens element and the second aperture stop.

According to another feature of the present invention, a two position variable focal length lens includes a common lens element moveably positioned on an optical axis. A wide angle lens element having aspheric surfaces is moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element. A telephoto lens element having aspheric surfaces is moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element. A magnification ratio change is effected by moving the common lens element along the optical axis and switching between the wide angle lens element located at the first position on the optical axis and the telephoto lens element located at the second position on the optical axis. The aspheric surfaces of the telephoto lens element have base radii that are larger than corresponding base radii of the aspheric surfaces of the wide angle lens element.

According to another feature of the present invention, a two position variable focal length lens includes a common lens element moveably positioned on an optical axis. A wide angle lens element is moveable between a first location removed from the optical axis and a first position on the optical axis on an image side of the common lens element. A telephoto lens element is moveable between a second location removed from the optical axis and a second position on the optical axis on the image side of the common lens element, wherein a magnification ratio change is effected by moving the common lens element along the optical axis and switching between the wide angle lens element located at the first position on the optical axis and the telephoto lens element located at the second position on the optical axis. The two position variable focal length lens satisfies the following condition: fC>((fZW+fZT)/2), where fCis a focal length of the common lens element, fZWis a focal length of the two position variable focal length lens in a wide angle position, and fZTis a focal length of the two position variable focal length lens in a telephoto position.

According to another feature of the present invention, a method of changing a magnification ratio from a wide angle position to telephoto angle position includes providing a common lens element positioned at a first location on an optical axis; providing a wide angle lens element located at a first position on the optical axis on an image side of the common lens element; providing a telephoto lens element located at a location removed from the optical axis; moving the common lens element toward an object plane; moving the telephoto lens element to a second position on the optical axis on the image side of the common lens clement; and removing the wide angle lens from the optical axis.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.

Referring toFIGS. 1A and 1B, a two position variable focal length lens20is shown. The two position variable focal length lens20includes a first lens unit22and a second lens unit24, as viewed from an object side of the two position variable focal length lens20. As shown inFIG. 1A, the first lens unit22includes a common lens element26while the second lens unit24includes a wide angle lens element28. An aperture stop30is positioned between common lens element26and wide angle lens element28. As shown inFIG. 1B, the first lens unit22includes the common lens element26while the second lens unit24includes a telephoto lens element32. A second aperture stop34is positioned between the common lens element26and the telephoto lens element32. Image plane36is cylindrically curved.

Zooming in and zooming out are accomplished by moving the common lens element26along a optical axis38while switching between wide angle lens element28and telephoto lens element32. For example, as shown inFIG. 1A, two position variable focal length lens20is in a wide angle position. As such, two position variable focal length lens20includes aperture stop30positioned between common lens element26and wide angle lens element28. When a telephoto position is desired, common lens element26moves toward object plane40in a direction as indicated by arrow42while wide angle lens28moves out of the optical axis38in a direction as indicated by arrow44. As this is occurring, telephoto lens element32(shown in phantom inFIG. 1A) moves into optical axis38in a direction as indicated by arrow46after common lens element26is located on the object side of telephoto lens element32. This completes the zoom in process which results in the two position variable focal length lens20being in a telephoto position, as shown in FIG.1B.

When a wide angle position is desired, the telephoto lens element32moves out of the optical axis38in a direction as indicated by arrow48while common lens element26moves toward image plane36in a direction as indicated by arrow50. Wide angle lens element28moves into optical axis38in a direction as indicated by arrow52such that common lens element26is on the object side of wide angle lens element32. This completes the zoom out process which results in the two position variable focal length lens20being in the wide angle position as shown in FIG.1A.

While the motion of the wide angle lens element28and the telephoto lens element32is generally perpendicular to the optical axis38, other motion angles can be incorporated with substantially similar results. The motion of common lens element26is generally parallel to optical axis38. Additionally, aperture stop30moves into and out of optical axis38with wide angle lens element28while second aperture stop34moves into and out of optical axis38with telephoto lens element32. Finally, common lens element26does not stop at a mid-range position. The movement of two position variable focal length lens20is from a wide angle position directly to a telephoto position or directly from a telephoto position to a wide angle position.

Referring toFIGS. 2A and 2B, a first example of the two position variable focal length lens20is shown.FIG. 2Ashows two position variable focal length lens20in a wide angle format or position whileFIG. 2Bshow two position variable focal length lens20in a telephoto format or position. Common lens element26is glass and includes surface S1which is spherical and convex toward the object plane40while surface S2is piano. Wide angle lens element28is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (styrene) and includes surfaces S5Aand S6Awhich are both aspheric.

A second example is also shown inFIGS. 2A and 2B. In this example, common lens element26is glass and includes surface S1which is spherical and convex toward the object plane40while surface S2is piano. Wide angle lens element28is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (for example, acrylic or PMMA, etc.) and includes surfaces S5Band S6Bwhich are both aspheric.

EXAMPLES 1 and 2

In wide angle format, Examples 1 and 2 have a cylindrically curved image plane with a radius=−120.0; a semi-field of 36.45°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element28has a focal length of 65.834 mm.

In telephoto1format, Example 1 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.66°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element32has a focal length of −727.007 mm.

In telephoto2format, Example 2 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.64°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000, and the second lens element32has a focal length of −642.625.

Referring toFIGS. 3A-3C, MTF performance plots are measured at best focus using weighted wavelengths (440 nanometers at 15%, 546.1 nanometers at 50%, and 650 nanometers at 35%) at a frequency of 4.45 cycles per millimeter with full field (100%) being 20.58 mm.FIG. 3Ashows MTF plots for Examples 1 and 2 in wide angle format.FIG. 3Bshows MTF plots for Example 1 in telephoto (telephoto1) format.FIG. 3Cshows MTF plots for Example 2 in an alternative telephoto (telephoto2) format. MTF plots are centered along the diagonal of the film cylinder (long dimension of 24×36 mm image format is measured along cylinder radius of curvature in all examples).

FIGS. 4A-4Cdescribe additional performance characteristics of the variable focal length lens20of Examples 1 and 2.FIG. 4Ashows lateral color correction for Examples 1 and 2 in wide angle format.FIG. 4Bshows lateral color correction for Example 1 in telephoto (telephoto1) format.FIG. 4Cshows lateral color correction for Example 1 in the alternative telephoto (telephoto2) format.

Referring toFIGS. 5A and 5B, a third example of the two position variable focal length lens20is shown.FIG. 5Ashows two position variable focal length lens20in a wide angle format or position whileFIG. 5Bshow two position variable focal length lens20in a telephoto format or position. Common lens element26is a meniscus glass lens and includes spherical surfaces S1and S2with surface S1being convex toward the object plane40. Wide angle lens element28is plastic (for example, acrylic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (for example, acrylic or PMMA, etc.) and includes surfaces S5and S6which are both aspheric.

In wide angle, Example 3 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 36.55°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element28has a focal length of 70.131 mm.

In telephoto, Example 3 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.38°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element32has a focal length of −304.786 mm.

Referring toFIGS. 6A-6B, MTF performance plots are measured at best focus using weighted wavelengths (440 nanometers at 15%, 546.1 nanometers at 50%, and 650 nanometers at 35%) at a frequency of 4.45 cycles per millimeter with full field (100%) being 20.58 mm.FIG. 6Ashows MTF plots for Example 3 in wide angle format.FIG. 6Bshows MTF plots for Example 3 in telephoto format. MTF plots are centered along the diagonal of the film cylinder (long dimension of 24×36 mm image format is measured along cylinder radius of curvature in all examples).

FIGS. 8A-8Bdescribe additional performance characteristics of the variable focal length lens20of Example 3.FIG. 8Ashows lateral color correction for Example 3 in wide angle format.FIG. 8Bshows lateral color correction for Example 3 in telephoto format.

Again referring toFIGS. 5A and 5B, a fourth example is shown. Common lens element26is a meniscus glass lens and includes spherical surfaces S1and S2with surface S1being convex toward the object plane40. Wide angle lens element28is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (styrene) and includes surfaces S5and S6which are both aspheric.

In wide angle, Example 4 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 36.52°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element28has a focal length of 72.521 mm.

In telephoto, Example 4 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.35°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element32has a focal length of −283.278 mm.

Referring toFIGS. 7A-7B, MTF performance plots are measured at best focus using weighted wavelengths (440 nanometers at 15%, 546.1 nanometers at 50%, and 650 nanometers at 35%) at a frequency of 4.45 cycles per millimeter with full field (100%) being 20.58 mm.FIG. 7Ashows MTF plots for Example 4 in wide angle format.FIG. 7Bshows MTF plots for Example 4 in telephoto format. MTF plots are centered along the diagonal of the film cylinder (long dimension of 24×36 mm image format is measured along cylinder radius of curvature in all examples).

FIGS. 9A-9Bdescribe additional performance characteristics of the variable focal length lens20of Example 4.FIG. 9Ashows lateral color correction for Example 4 in wide angle format.FIG. 9Bshows lateral color correction for Example 4 in telephoto format.

Referring toFIGS. 10A and 10B, a fifth example of the two position variable focal length lens20is shown.FIG. 10Ashows two position variable focal length lens20in a wide angle format or position whileFIG. 10Bshows two position variable focal length lens20in a telephoto format or position. Common lens element26is glass, biconvex, and includes spherical surfaces S1and S2. Wide angle lens clement28is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S5and S6which are both aspheric.

In wide angle, Example 5 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 36.51°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element28has a focal length of 66.395 mm.

In telephoto, Example 5 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.83°; and a semi-diagonal of 21.63 (Ilum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element32has a focal length of −946.925 mm.

Referring toFIGS. 11A-11B, MTF performance plots are measured at best focus using weighted wavelengths (440 nanometers at 15%, 546.1 nanometers at 50%, and 650 nanometers at 35%) at a frequency of 4.45 cycles per millimeter with full field (100%) being 20.58 mm.,FIG. 11Ashows MTF plots for Example 5 in wide angle format.FIG. 11Bshows MTF plots for Example 5 in telephoto format. MTF plots are centered along the diagonal of the film cylinder (long dimension of 24×36 mm image format is measured along cylinder radius of curvature in all examples).

FIGS. 13A-13Bdescribe additional performance characteristics of the variable focal length lens20of Example 5.FIG. 13Ashows lateral color correction for Example 5 in wide angle format.FIG. 13Bshows lateral color correction for Example 5 in telephoto formal

Again referring toFIGS. 10A and 10B, a sixth example is shown. Common lens element26is glass, biconvex, and includes spherical surfaces S1and S2. Wide angle lens element28is plastic (for example, acrylic plastic or PMMA, etc.) and includes surfaces S3and S4which are both aspheric. Telephoto lens element32is plastic (styrene) and includes surfaces S5and S6which are both aspheric.

In wide angle, Example 6 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 35.87°; and a semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens element26has a focal length of 40.000 mm, and the second lens element28has a focal length of 65.496 mm.

In telephoto, Example 6 has a cylindrically curved image plane with a radius=−120.0; a semi-field of 24.70°; and a. semi-diagonal of 21.63 (Illum.), 20.58 (Image). The first lens clement26has a focal length of 40.000 mm, and the second lens element32has a focal length of −1060.655 mm.

Referring toFIGS. 12A-12B, MTF performance plots are measured at best focus using weighted wavelengths (440 nanometers at 15%, 546.1 nanometers at 50%, and 650 nanometers at 35%) at a frequency of 4.45 cycles per millimeter with full field (100%) being 20.58 mm.FIG. 12Ashows MTF plots for Example 6 in wide angle formatFIG. 12Bshows MTF plots for Example 6 in telephoto format. MTF plots are centered along the diagonal of the film cylinder (long dimension of 24×36 mm image format is measured along cylinder radius of curvature in all examples).

FIGS. 14A-14Bdescribe additional performance characteristics of the variable focal length lens20of Example 6.FIG. 14Ashows lateral color correction for Example 6 in wide angle format.FIG. 14Bshows lateral color correction for Example 6 in telephoto format.

The common lens element26of the two position variable focal length lens20has an image side surface S2that preferably satisfies the condition (1/−20.8)≦c≦(1/5), where c is the curvature of the image side surface. More preferably, the common lens element26satisfies the condition (1/−76)≦c≦(1/18.7), where c is the curvature of the image side surface S2. Still more preferably, the common lens element26satisfies the condition: (1/−100)≦c≦(1/25.5), where c is the curvature of the image side surface S2, and more preferably, the common lens element26satisfies the condition: c=0, where c is the curvature of the image side surface S2of the common lens element26.