DEVICE FOR CAPTURING A LONG EXPOSURE IMAGE

Abstract

The invention relates to a field of capturing images requiring a long exposure, e.g., when photographing faint objects. The device comprises an image formation unit, an image capture unit, a primary shutter and a secondary shutter connected to at least one disturbance detector via a control unit.

Claims

1-10. (canceled)

11. A device for capturing long-exposure images comprising: an image capture unit; an image formation unit in front of the image capture unit; a primary shutter in front of the image capture unit; a secondary shutter in front of the image capture unit; a control unit connected to the secondary shutter and configured to close and open the secondary shutter depending on a signal received from a disturbance detector.

12. The device of claim 11, wherein the secondary shutter is in front of the image formation unit.

13. The device of claim 11, wherein the secondary shutter is between the image formation unit and the image capture unit.

14. The device of claim 11, wherein the secondary shutter is integrated with the image formation unit.

15. The device of claim 11, wherein the secondary shutter is faster than the primary shutter.

16. The device of claim 11, wherein the disturbance detector is a part of the device.

17. The device of claim 11, wherein the disturbance detector detects vibration.

18. The device of claim 11, wherein the disturbance detector detects pulsed light sources.

19. The device of claim 11, wherein the disturbance detector tracks satellites.

20. The device of claim 11, wherein the disturbance detector monitors objects capable of distorting the image.

21. The device of claim 11, wherein the control unit is further connected to the primary shutter and configured to control both the primary shutter and the secondary shutter.

22. The device of claim 11, wherein the disturbance detector is physically separate from the image capture unit, the image formation unit, the primary shutter, the secondary shutter and the control unit.

Description

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0021] In the drawings:

[0022] FIG. 1 represents a schematic diagram of a device for capturing long-exposure images having a secondary shutter.

[0023] FIG. 2 represents a drawing illustrating operation of a secondary shutter mounted on a telescope.

[0024] FIG. 3 represents a schematic diagram of controlling a secondary shutter using disturbance detectors, illustrated in example of a telescope.

[0025] FIG. 4 represents a schematic diagram of a device for capturing long-exposure images, wherein a control unit controls a primary shutter, a secondary shutter and an image capture unit.

[0026] FIG. 5 represents an operation time diagram for the device with a secondary shutter.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0027] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0028] A device for capturing long-exposure images (FIG. 1) includes an image formation unit (1), e.g., a lens; an image capture unit (2), e.g., a detector; and a shutter (3) such as a primary shutter providing start and end of integration mode in the image capture unit (2). The image capture unit (2) may be implemented, based on photosensitive arrays, in particular, based on CCD matrix technology.

[0029] Usually, devices for capturing long-exposure images use primary shutters (3) implemented as electronic, mechanical, electromechanical or electronic-optical shutters, which are typically low-speed shutters (e.g., curtain shutters) able to exclude impact of vibrations, electromagnetic radiation, heat and other negative factors related to high-speed devices on operation of the image capture unit. Alternatively, they may be electronic shutters embedded into the device for capturing long-exposure images, where a transition to closed state means not only an interruption of input flow of electromagnetic energy that a photosensitive array is exposed to, but also cancelling integration of that energy and further losing the integrated energy.

[0030] The device for capturing long-exposure images according to the invention also comprises a secondary shutter (4) that is connected to disturbance detectors (6) via a control unit (5). The secondary shutter (4) may be located anywhere upstream of the image capture unit (2). For example, it may be located in front of the image formation unit (1) (i.e., the lens) or embedded into the image formation unit (1) or located behind the image formation unit (1). In particular, it can be located at a distance from the image capture unit (2) so as mechanical oscillations of the secondary shutter (4), as well as thermal and electromagnetic energy radiated by it would not cause any substantial negative effect on the image capture unit (2).

[0031] Devices for capturing long-exposure images are mainly used in fields, where electromagnetic radiation has to be captured, in particular, in the range of light radiation of faint objects. These fields relate to astronomy and to microscopic photography (microscopy), in particular, to fluorescence microscopy.

[0032] FIG. 3 shows an example of the control unit (5) having the secondary shutter (4) and the disturbance detectors (6) for a telescope (12). A drawing illustrating this implementation example is provided in FIG. 2. Sometimes it happens that disturbance for capturing an image by a camera mounted in the telescope (12) is caused by artificial earth satellites (14) caught in the frame or by light pulses of outdoor pulse illumination systems (15), e.g., such as a system mentioned in RU patent 2662907, or when a seismic wave (13) generated by earthquake disturbs the telescope (12) and the image capture unit (2) (the detector) and thus causes shift of projected image of space objects in the image capture unit of the telescope.

[0033] The secondary shutter (4) is preferably a high-speed shutter (operating time 50 ms or less, preferably less than 30 ms) in order to reduce loss in exposure during switching and should provide a fast response to emerging sudden and short disturbances, i.e., it shall be able to repeatedly switch between open and closed states in a few milliseconds or faster (typically about 50 ms operation time, generally in the 30-100 ms range, but as a rule, the shorter the better). It may be provided as a mechanical or electromechanical device (like a curtain shutter, a lamellar shutter, a rotary shutter, etc.) or as an electronic-optical device (like a liquid crystal-based optical screen, etc.) or as another suitable device.

[0034] A disturbance detector (8) for seismic oscillations as well as for other oscillations of a base of any device, e.g., a microscope, may be provided as a vibration detector. A wind load detector (11) may also be provided as a vibration detector.

[0035] A disturbance detector (9) for glow of moving satellites may be provided as an object tracking detector. For instance, it may be provided as a device for surveying satellite orbits. Also, satellite orbits are known and available from public databases, e.g., from NORAD, and, thus, the timing of the satellite being in the field of view can be predicted accurately, for purposes of control unit (7) operation.

[0036] A disturbance detector (10) for light pollution by pulsed light sources may be provided as a detector for synchronizing with the pulsed light sources.

[0037] A control unit (7), i.e., a unit for control of the shutters and the image capture units (FIG. 4) may be configured to control the primary shutter, the secondary shutter and the detector of the image capture unit. In this case, it controls every switching the image capture unit (2) on and off.

[0038] The primary shutter (3) may also be an electronic switch embedded into the photosensitive array, so switching the array on and off means simultaneously switching the primary shutter on and off.

[0039] The device for capturing long-exposure images according to the diagram represented in FIG. 1 operates as follows.

[0040] Initially, the secondary shutter (4) is in an open state. It remains so until an instruction comes from any of the disturbance detectors (8, 9, 10, 11).

[0041] Further, the photosensitive array of the image capture unit (2) is activated (FIG. 2, FIG. 4, FIG. 5). The photosensitive array remains active while the image capturing device operates, even when the device is exposed to external disturbances. As it was mentioned, deactivation of the array causes loss of the integrated light energy and the process shall be started from the very beginning. Thus, the process of capturing image begins by opening the primary shutter (3) for time T (FIG. 5 (A)). Usually, the primary shutter (3) is not a fast shutter in such devices. If a disturbance occurs, a corresponding detector triggers. For example, it may be the seismic oscillations detector (8) (FIG. 5 (B)), the satellite tracking detector (9) (FIG. 5 (C)) or the outdoor illumination system detector (10) (FIG. 5 (D)). Triggering any of these detectors causes a closing of the secondary shutter (4) (FIG. 5 (E)), so integration of a polluted or shifted image is blocked. The photosensitive array of the image capture unit (2) remains active. The primary shutter (3) remains open. Further, when the disturbance is over, the corresponding disturbance detector (unit 8, 9 or 10) sends a signal to the control unit (5) that generates an instruction to open the secondary shutter (4). The secondary shutter (4) opens and exposure resumes until a next disturbance occurs, i.e., until a next closing instruction comes from the control unit (5). The primary shutter (3) remains open until the end of exposure, independently on occurrence of the disturbances.

[0042] FIG. 5 (F) shows a long process of integration of charge by the photosensitive array in the image capture unit (2) for a faint object. Curve (16) indicates a process of integration of charge by the photosensitive array, when glow of the object to be photographed is constant and when occurred disturbances are suppressed. Curve (17) indicates a case of absence of disturbances, so integration is not interrupted. Comparison of curves (16) and (17) shows that upon occurrence of disturbances, the process of integration of charge by the photosensitive array for a constant glow of the object to be photographed requires more time.

[0043] Implementation of the device according to the diagram in FIG. 4 provides possibility of compensation a time lost for switching off the secondary shutter (4) upon occurrence of any disturbances to assure a required exposure and to obtain an image of desired quality. In this case, the disturbance detector unit (6) is connected to the control unit (7) of the image capture unit (2), which is also a shutter control unit. The disturbance detector unit (6) sends a signal comprising interruption time of the secondary shutter (4) to the control unit (7). Thus, the control unit (7) allows increasing exposure time of the image capture unit (2) and compensating the time lost while the secondary shutter (4) is closed.

[0044] In order to prevent decreasing quality of capturing a certain frame, exposure time shall be extended by T.sub.comp=(T1+T2+T3+ . . . ), where T1, T2 and T3 are time periods when the secondary shutter (4) is closed upon occurrence of disturbances.

[0045] The control unit (7) according to the diagram represented in FIG. 4 extends time T (open time of the primary shutter (3)) by length of T.sub.comp. When implemented in such a way, the control unit (7) is able to control the image capture unit (2).

[0046] Additionally to the vibration disturbance detector of the device, a disturbance detector for inadvertently switched illumination may be used, which is per se an illumination synchronization detector.

INDUSTRIAL APPLICABILITY

[0047] The invention may be implemented in various commercially applicable devices, as well in newly developed devices.

[0048] Having thus described a preferred embodiment, it should be apparent to those skilled in the art that certain advantages of the described method and apparatus have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention.