Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
1999-02-05
2001-05-22
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C359S660000, C359S661000, C359S781000, C359S782000
Reexamination Certificate
active
06236521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an objective lens and an image pickup device using the same and is appropriate in particular to a camera system in a device using an image pickup element such as digital still camera, a video camera, a broadcasting camera or a photograph camera with an exit pupil kept far apart from the image field while widening an angle of field devised by employing the retro-focus type.
2. Related Background Art
Recent years, a digital still camera has been spreading out as the image input device. In this digital still camera there is generally carried out a process comprising AD-converting an output signal from a solid image pickup element such as CCD into image data, subjecting them to an image compression such as JPEG and storing the compressed data in a storage medium such as flash memory. After being developed on a computer, the compressed data thus stored are displayed on a monitor or the like.
In such a digital still camera, a higher precision of photographed images and a smaller size of image pickup devices has recently become a task and the compatibility of a high resolution and a smaller size is required therewith. Especially, to attain a thin model camera with stress laid on the portability, shortening the total lens length is required in a photographing lens (objective lens). For shortening the total lens length, it is advantageous to use an objective lens having as small a number of constituent lenses as possible.
Besides, as objective lenses for implementing a wide angle of field, many retro-focus type ones composed of a front lens unit having a negative refractive power and a rear lens unit having a positive refractive power are known. Especially as retro-focus type objective lenses having a small number of constituent lenses, those of the above front lens unit comprising one negative lens are proposed.
As such retro-focus type objective lenses with a front lens unit comprising one negative lens, for example, a 3 group 3 piece configuration comprising a negative lens, a positive lens and a positive lens in sequence from the object side is disclosed in U.S. Pat. No. 5,418,649 and a 3 group 4 piece configuration comprising a negative lens, a positive lens and a positive composite lens in sequence from the object side is disclosed in another embodiment of the same U.S. Pat. No. 5,418,649. As other examples, Japanese Patent Publication No. 7-122692 (corresponding to U.S. Pat. No. 4,984,878), Japanese Patent Publication No. 5-37288, Japanese Patent Publication No. 5-20724, Japanese Patent Publication No. 61-46807, Japanese Patent Publication No. 58-7 and Japanese Patent Application Laid-Open No. 9-189856 (corresponding to U.S. Pat. No. 5,706,141), U.S. Pat. No. 4,146,304, U.S. Pat. No. 4,674,844 and Japanese Patent Publication No. 60-32165 (corresponding to U.S. Pat. No. 4,130,349) disclose a 4 group 4 piece configuration comprising: a negative lens, a positive lens, a positive lens and a positive lens in sequence from the object side; a 4 group 4 piece configuration comprising:
a negative lens, a positive lens, a negative lens and a positive lens in sequence from the object side;
a 4 group 4 piece configuration comprising:
a negative lens, a positive lens, a positive lens and a negative lens in sequence from the object side;
a 4 group 5 piece configuration comprising: a negative lens, a positive lens, a positive lens and a positive composite lens in sequence from the object side;
a 4 group 5 piece configuration comprising:
a negative lens, a positive lens, a negative composite lens and a positive lens in sequence from the object side;
a 4 group 5 piece configuration comprising:
a negative lens, a positive lens, a positive composite lens and a negative lens in sequence from the object side; and
a 5 group 5 piece configuration comprising:
a negative lens, a positive lens, a negative lens, a positive lens, and a positive lens in sequence from the object side, respectively. All of them are of retro-focus model and consist of a negative front lens unit and a positive rear lens unit.
Besides, the focusing approach is divided into the pan focus approach with the pint fixed at an ultrafocal length and a method for focusing by driving the focusing lens for each release. Generally, in a digital still camera of much consumed power, it is desired to lengthen the service life of a battery and the pan focus is effective for saving the power consumption. To obtain an image of high resolution, however, focusing is preferably made so as to make the pint best according to the object distance. Especially, in the case of a macro photographing with an objective lens small in shortest object distance, those of focusing mechanism is better than those of pan focus.
As regards a retro-focus type objective lens, the total thrust method by moving the whole lens system is well known. Besides, as a method of making a partial thrust while making a total thrust and a rear focus method by thrusting a lens on the image side, Japanese Patent Publication No. 45-39875 and Japanese Patent Application Laid-Open No. 55-143517 are referred to.
Besides, as a method for the thinnest possible image pickup device in optical axis, a collapsible mount method comprising moving the objective lens toward the imaging surface side and collapsing it into the front cover of a camera when not using is well known. To minimize the drive mechanism including the actuator of lenses in the collapsible mount method, it is effective to make the focus mechanism and the collapsible mount mechanism into common use by collapsing the focusing lens in a single focus lens.
In the photographing system using a solid image pickup element, the incident angle to the receiving surface of an off-axis ray increases with a smaller distance from the image field to the exit pupil, so that a problem of shading or the like takes place. Thus, the objective lens of a image pickup system using such an image pickup element must be chosen to a telecentric optical system with an exit pupil kept sufficiently apart from the image field. To be specific, the objective lens is so arranged preferably that the off-axis chief ray incident to the optical axis at an angle corresponding to the photographing face angle reaches the image pickup element forming an imaging surface nearly in parallel with the optical axis. The wider the photographing face angle is, the stronger the refractive power required for such a refraction of an off-axis chief ray as to become in parallel with the optical axis is.
Generally, affording a negative refractive power to a group of lenses on the object side from the stop and a positive refractive power to a group of lenses on the image field side from the stop is advantageous to the reduction of an angle of an off-axis chief ray with the optical axis, i.e., to make it nearly parallel to the optical axis. Namely, in a retro-focus type objective lens, the front group of a negative refractive power is generally disposed on the object side with respect to the stop and accordingly the angle of an off-axis chief ray with the optical axis can be reduced in presence of this front group. In the positive rear group, the angle of an off-axis chief ray with the optical axis can be reduced under action of positive lenses on the image field side with respect to the stop. Since both the front lens unit and the rear lens unit have an effect of making the exit pupil apart from the image field side, the retro-focus type optical system is very effective in the case of a wide photographing face angle.
Furthermore, for making the exit pupil sufficiently apart from the image field by shortening the total lens length, it is preferable to set at least the final lens of the rear group to a positive lens. More preferably, the surface on the image field side of the lens directly in front of the final lens is set to a convex surface. In such a manner, since the action of refracting an off-axis chief ray can be shared between the surfaces of three lenses including the final lens, the refrac
Canon Kabushiki Kaisha
Epps Georgia
Fitzpatrick ,Cella, Harper & Scinto
Thompson Tim
LandOfFree
Objective lens and image pickup device using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Objective lens and image pickup device using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Objective lens and image pickup device using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2437157