Method of automatically tracking and photographing celestial objects and camera employing this method

• US 8,717,441 B2
• Filed: 05/17/2011
• Issued: 05/06/2014
• Est. Priority Date: 05/19/2010
• Status: Active Grant

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Pentax Ricoh Imaging Americas Corporation (Ricoh Company Limited)
• Inventors: Ohta, Makoto
• Primary Examiner(s): Patel, Jayanti K
• Assistant Examiner(s): Aghevli, Reza
• Application Number:
  US13/109,247
• Publication Number:
  US 20110285855A1
• Time in Patent Office: 1,085 Days
• Field of Search: 348/169, 348/208.6, 348/208.2, 348/216.1, 348/E05.024, 348/E5.034, 348/E5.046
• US Class Current: 348/169
• CPC Class Codes: G01S 3/782 Systems for determining direction or deviation from predetermined direction
• CPC Class Codes: G01S 3/7864 T.V. type tracking systems
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors

Abstract

A method of automatically tracking and photographing a celestial object so that the celestial object image, which is formed on an imaging surface of an image sensor via a photographing optical system, becomes stationary relative to a predetermined imaging area of the imaging surface of the image sensor during a tracking and photographing operation. The method includes performing a preliminary photographing operation at a predetermined preliminary-photographing exposure time with the photographic apparatus directed toward the celestial object and with a celestial-body auto tracking action suspended to obtain a preliminary image before automatically tracking and photographing the celestial object, calculating a moving direction and a moving speed of the celestial object image from the preliminary image that is obtained by the preliminary photographing operation, and automatically tracking and photographing the celestial object based on the moving direction and the moving speed of the celestial object image.

Claims

1. A method of automatically tracking and photographing a celestial object which moves relative to a photographic apparatus due to diurnal motion so that a celestial object image, which is formed on an imaging surface of an image sensor via a photographing optical system, becomes stationary relative to a predetermined imaging area of the imaging surface of the image sensor during a tracking and photographing operation, the method comprising:

performing a preliminary photographing operation for a predetermined preliminary-photographing exposure time with said photographic apparatus directed toward said celestial object and with a celestial-body auto tracking action suspended to obtain a preliminary image before automatically tracking and photographing said celestial object;

calculating a moving direction and a moving speed of the celestial object image from said preliminary image that is obtained by said preliminary photographing operation; and

automatically tracking and photographing said celestial object based on the calculated moving direction and the calculated moving speed of the celestial object image.

2. The method according to claim 1, wherein said automatically tracking and photographing comprises automatically tracking and photographing while moving at least one of said predetermined imaging area of said imaging surface of the image sensor and an image-forming position of the celestial object image relative to said photographic apparatus based on the calculated moving direction and the calculated moving speed of the celestial object image.

3. The method according to claim 1, wherein said calculating of said moving direction and said moving speed of the celestial object image from said preliminary image comprises calculating from positions of first images of at least two celestial objects which are formed on said imaging surface at a commencement of said preliminary photographing operation and positions of second images of said at least two celestial objects which are formed on said imaging surface after a lapse of a predetermined period of time from said commencement of said preliminary photographing operation.

4. The method according to claim 3, wherein points S1 and S2 designate said positions of said first images of said two celestial objects, points S1′

and S2′

designate said positions of said second images of said two celestial objects, point O designates an arbitrary point on said preliminary image at said commencement of said preliminary photographing operation that is different from said points S1 and S2, and Δ

t designates a period of time from said commencement of said preliminary photographing operation until a termination of the preliminary photographing operation, said calculating of said moving direction and said moving speed of the celestial object image from said preliminary image comprising;

calculating an angle Δ

θ

between a straight line passing through points S1 and S2 and a straight line passing through points S1′ and

S2′

, wherein said angle Δ

θ

defines an angle of rotation of the celestial object image; and

calculating a distance between said point O and a point O′

of three points forming a triangle Δ

S1′

S2′

O′

that is congruent to a triangle Δ

S1S2O defined by said points S1, S2 and O as an image shifting amount of the celestial object image.

5. The method according to claim 4, further comprising:

calculating and determining a movement amount and an angle of rotation of the celestial object image which occur during an actual-photographing exposure time, which exceeds said preliminary-photographing exposure time, by calculating an average of movement amounts and rotation angles of said two celestial object images that are obtained by performing said preliminary photographing operation a plurality of times.

6. The method according to claim 4, further comprising:

calculating and determining a movement amount and an angle of rotation of the celestial object image which occur during an actual-photographing exposure time, which exceeds said preliminary-photographing exposure time, from a rate of change in movement amounts and rotation angles of said two celestial object images that are obtained by performing said preliminary photographing operation a plurality of times.

7. The method according to claim 3, wherein, in an X-Y coordinate system in which horizontal and vertical axes of said imaging surface having a rectangular shape represent an X-axis and a Y-axis, respectively, points S1 and S2 designate said positions of said first images, points S1′

and S2′

designate said positions of said second images after a lapse of a time Δ

t from a commencement of a preliminary photographing operation, points S1″ and

S2″

designate positions of third images of said at least two celestial objects which are formed on said imaging surface after a lapse of a time (2×

Δ

t) from a commencement of the preliminary photographing operation, and point O designates an arbitrary point on said preliminary image at said commencement of said preliminary photographing operation that is different from said points S1 and S2,

said calculating of said moving direction and said moving speed of the celestial object image from said preliminary image further comprises determining coordinates Xt and Yt of predicted center points O′ and

O″

, . . . of said imaging surface after a lapse of an exposure time T from said point O from the following equations;

Xt=X0−

r×

sin(Θ

+Δ

φ

/Δ

t×

T)

Yt=Y0+r×

cos(Θ

+Δ

φ

/Δ

t×

T)

wherein X0 and Y0 designate x and y coordinates of a point of intersection G between a perpendicular bisector of a segment O-O′ and

a perpendicular bisector of a segment O′

-O″

, and Θ

designates an angle between a straight line which passes through said intersection point G and is parallel to said Y-axis and a straight line G-O which connects said point O and said intersection point G.

8. The method according to claim 1, wherein said performing of said preliminary photographing operation comprises one of performing a plurality of exposures at predetermined intervals, and photographing at least two images and synthesizing said two images into a single image.

9. The method according to claim 1, wherein said performing of said preliminary photographing operation comprises:

one of temporarily opening an aperture of an adjustable diaphragm of a photographing lens, in which said photographing optical system is provided, and temporarily increasing a photographic sensitivity to increase an amount of exposure at each of a commencement of said preliminary photographing operation and a termination of the preliminary photographing operation, during said preliminary photographing operation.

10. The method according to claim 1, wherein said performing of said preliminary photographing operation comprises:

one of temporarily repeatedly opening an aperture of an adjustable diaphragm of a photographing lens, in which said photographing optical system is provided, and temporarily repeatedly increasing a photographic sensitivity to increase an amount of exposure repeatedly at predetermined intervals.

11. A camera employing the method according to claim 1, comprising:

a photographing system which performs said preliminary photographing operation and automatically tracks and photographs said celestial object; and

a controller which performs said calculating of the moving direction and the moving speed.

12. The camera according to claim 11, wherein said photographing system comprises said photographing optical system which includes a photographing lens and an adjustable diaphragm, wherein said controller controls an aperture size of said adjustable diaphragm.

13. The camera according to claim 11, wherein said photographing system comprises an image-sensor mover which linearly moves said image sensor in directions orthogonal to an optical axis of said photographing optical system and rotates about an axis parallel to said optical axis based on said moving direction and said moving speed of said celestial object image.

14. The method according to claim 1, wherein the preliminary image obtained during the preliminary photographing operation is not used in the automatically tracking and photographing the celestial object.