Patent Grant
12085706
The technical field of the invention is a viewfinder, designed to equip image-forming devices, for example an image-recording apparatus, or devices such as binoculars or spotting scopes. The viewfinder may be applied to specific devices, for example a medical imaging device or a weapon.
Cameras generally comprise viewfinders, allowing a user to view the field of observation of the camera.
It may be a question of an optical viewfinder, which forms an image from light rays coming from the observed scene, and having propagated through the objective of the camera. The light rays directed into the viewfinder originate directly from the observed scene. They may be reflected by a splitter placed between the objective and the image sensor of the camera. It is an optical viewfinder, because it is designed using optical elements (reflectors, dioptric interfaces). Certain optical viewfinders use a dedicated objective, different from the objective associated with the sensor of the camera. The image of the scene, produced by this type of viewfinder, is affected by a parallax with respect to the image formed on the image sensor. However this parallax is generally negligible, except when the observed scene is very close.
Another type of viewfinder is the electronic viewfinder, in which the viewfinder uses a display, displaying an image representative of the image formed on the image sensor of the camera. Whereas optical viewfinders allow the observed scene to be viewed, electronic viewfinders allow the image that will potentially be recorded by the image sensor to be seen. This may allow the user to adjust the camera and to view the effect of the adjustments directly in the image produced by the viewfinder. The adjustments may for example relate to management of image composition, depth of field, or white balance.
Generally, a camera comprising an optical viewfinder comprises a display, integrated into the body of the camera. The user must then alternate between viewing through the optical viewfinder and viewing the display. He must therefore memorize one of the two images in order to make the comparison with the other image.
When the camera comprises only an electronic viewfinder, the user must remove his eye from the viewfinder to observe the scene that he desires to photograph.
Certain cameras allow, in a given viewfinder, the image of the optical viewfinder, representative of the observed scene, and the image of the electronic viewfinder, representative of the image formed on the image sensor of the camera, to be switched between. Such switching does not allow images produced by both types of viewfinder to be displayed simultaneously. Thus, comparison of the two images remains tedious.
Certain viewfinders have been designed, combining an optical viewfinder and an electronic viewfinder. In this type of viewfinder, the image produced by the electronic viewfinder appears in a frame, taking the form of a thumbnail superposed on one portion of the direct image, produced by the optical viewfinder. The superposition masks one portion of the direct image. Moreover, the image of the electronic viewfinder is displayed in the form of a thumbnail, the dimensions of which are small with respect to the image of the optical viewfinder. This does not allow a good comparison to be made between the two images.
The invention described below improves the possibilities of comparison of two images, corresponding to a given scene, while involving a minimal movement of the eye, the latter never being removed from the viewfinder. One particular application regards photography, the invention improving the possibilities of comparison between the image of the observed scene and the image perceived by the image sensor. Other possible applications are described at the end of the description, the aim being to facilitate comparison of two different images.
A first subject of the invention is a viewfinder, intended to be placed facing an eye of a user of an observing device, the observing device comprising an observation objective intended to form an image of an observed scene, the viewfinder comprising:
Preferably, the first optical axis and the second optical axis are coplanar. Preferably, the first optical axis and the second optical axis lie in a vertical or horizontal plane.
According to one embodiment:
Preferably, the first optical axis and the second optical axis are inclined with respect to each other by an angle of inclination smaller than 40°.
According to one embodiment:
According to one embodiment, referred to as the image-capturing embodiment:
According to one possibility:
According to one possibility:
The auxiliary objective may have an optical axis parallel to the optical axis of observation.
According to one possibility:
According to one possibility, the image-capturing apparatus comprises a unit for controlling the image sensor. The viewfinder comprises:
The first optical system may extend to a first exit dioptric interface, the first exit dioptric interface being positioned at a distance larger than or equal to 15 mm from the first exit pupil. The second optical system may extend to a second exit dioptric interface, the second exit dioptric interface being positioned at a distance larger than or equal to 15 mm from the second exit pupil.
In an observing embodiment, which is modular,
A second subject of the invention is an observing device, comprising an observation objective, intended to form an image of an observed scene, about an optical axis of observation, the observing device comprising a viewfinder according to the first subject of the invention.
The observing device may be a camera comprising an image sensor. The image sensor is configured to acquire the image of the observed scene, formed by the observation objective. The observing device comprises a viewfinder according to the image-capturing embodiment described with reference to the first subject of the invention.
The observing device may be magnifying, the first optical system and the observation objective being one and the same, the observing device comprising a viewfinder according to the modular embodiment described with reference to the first subject of the invention.
The invention will be better understood on reading the text describing examples of embodiment that are given, in the rest of the description, with reference to the figures listed below.
The invention is based on the fact that under the effect of a simple rotation, the eye is able to successively view a plurality of juxtaposed images, the user remaining immobile facing the viewfinder. Thus, the viewfinder is configured to simultaneously project:
Such a viewfinder is dual, because it allows two juxtaposed images to be observed simultaneously.
The viewfinder is configured to define a first exit pupil PS1 and a second exit pupil PS2, extending about the first optical axis A1 and the second optical axis A2, respectively.
Each exit pupil defines a region in which the image is complete and not thumbnailed when the eye is placed there.
The first exit pupil and the second exit pupil are tangent to the same spherical surface S that may be likened to the external surface of an eye. The diameter of the spherical surface S corresponds to the diameter of the eye, i.e. to about 25 mm, and more generally is comprised between 15 mm and 30 mm. In
The first optical axis A1 and the second optical axis A2 are secant. They converge at a point of convergence C forming the centre of the spherical surface S. Thus, when the user occupies the position of use of the viewfinder, the point of convergence C is located inside the eye. Advantageously, the point of convergence C corresponds to the centre of rotation of the eye, or lies in a central region of the eye of the user. By central region, what is meant is a region extending to within 5 mm from the centre of rotation of the eye. Use of two secant optical axes allows two different images to be displayed, without superposition on each other. The images I1 and I2 are preferably close enough together to facilitate their comparison. The invention makes it possible to prevent the two images from superposing in order to avoid an effect of masking of one image by the other image.
The position of use of the viewfinder is thus defined by the point of convergence of the two optical axes. It corresponds to the position in which the eye E is able to sequentially observe the two images, via a simple rotation.
Thus, when it occupies the position of use, via a simple rotation of his eye, the user views the first image I1, or the second image I2, by placing it facing the first exit pupil PS1 or facing the second exit pupil PS2, respectively. On account of the arrangement of the exit pupils, the user is able to successively observe the first image and the second image without moving his eye E with respect to the viewfinder, with the exception of a simple rotation. In
The first optical axis A1 and the second optical axis A2 are inclined with respect to each other by an angle of inclination θ. In this example, the first optical axis and the second optical axis are coplanar and belong to the same vertical plane. The angle of inclination θ corresponds to the angular offset of the first exit pupil and of the second exit pupil.
More generally, each image projected by the viewfinder, onto the eye, defines, parallel to a longitudinal axis X, a width, and, parallel to a lateral axis Y, a height. The first image I1 defines a width l1 and a height h1. The second image I2 defines a width l2 and a height h2. It is preferable for the first and second images to be aligned either along the lateral axis Y, as shown in
The configuration shown in
The central axis Δ corresponds to the orientation of the eye when the user is looking straight ahead. In the configuration of
The term optical system designates a set of refractive and/or reflective optical elements allowing the path of light rays to be modified. The first and second optical systems each define one optical channel.
In
One quantity to be considered is eye relief ER. In each optical system, the eye relief corresponds to the distance between the exit dioptric interface and the eye in the optimal position of use. Conventionally, allowance is made for an eye relief larger than or equal to 15 mm. Thus, the first exit dioptric interface 15 and the second exit dioptric interface 25 are centred on the first axis and on the second axis and are placed, respectively, at distances ER1 and ER2 larger than 15 mm from the spherical surface S to which the exit pupils PS1 and PS2 are tangent. Preferably ER1=ER2=ER.
In
The diameter Φ2 of the second exit dioptric interface 25 is obtained according to the expression:
ΦPS1 and ΦPS2 are the diameter of the exit pupils PS1 and PS2, respectively.
Typical values of Φ1 and of Φ2 may for example be comprised between 5 mm (setting ΦPS1=ΦPS2=4 mm; ER1=ER2=15 mm, and α=10°) and 25 mm (setting ΦPS1=ΦPS2=12 mm; ER1=ER2=22 mm, and α=41°).
Preferably, ΦPS1=ΦPS2, the values of ΦPS1 and ΦPS1 typically being comprised between 2 mm and 18 mm.
The angle of rotation of the eye θ corresponds to the angle described by the eye to pass from a position centred on the first optical axis A1 to a position centred on the second optical axis A2 and vice versa. The angle of rotation θ may be calculated using the expression:
where r is the ocular radius and Φ=Φ1=Φ2
The ocular radius r is considered to be equal to 12.5 mm, this corresponding to an ocular diameter of 25 mm.
The angle of rotation θ is preferably smaller than 40°, the value of 40° being a biological limit of the human eye. If the upper limit of 25 mm is used for ¢ (obtained by setting ER=22 mm and ΦPS1=ΦPS2=12 mm, and α=41°) then θ=72°. Such a rotation-angle value is too great. In order to limit the angle of rotation to 40°, the device must be dimensioned taking into account the following conditions:
Generally, the first optical system 10 is configured to project a first image I1, formed by an image-forming means, towards the eye. The light rays forming the first image reach the eye by propagating about the first axis A1. The first image I1 is representative of the observed scene. It may be formed from light rays incident on the image sensor 9. Thus, the first image I1 is independent of settings of the image sensor.
In the embodiment shown in
The first optical system 10 comprises a prism 12, typically a pentaprism, configured to orient the propagation of the light rays, forming the first image, parallel to the optical axis of observation AO, so that said rays reach the eye by propagating along the axis A1 parallel to the optical axis of observation AO. The optical system 10 may comprise one or more shaping dioptric interfaces 13 and the exit dioptric interface 15 described above.
In this embodiment, the viewfinder 1 acts as a passive viewfinder, or direct viewfinder: the rays propagating through the first optical system originate from the observed scene (the viewfinder has a “reflex” configuration). In this embodiment, the means for forming the first image I1 is the splitter 8 placed transversely to the optical axis of observation AO.
The first embodiment is suitable for applications in which the first image, resulting from the splitter 8, is an image acquired in a spectral band different from the image acquired by the image sensor 9. For example, the first image is formed in a fluorescence spectral band whereas the image acquired by the image sensor is an image, in all the visible spectrum, of the observed scene. In this case, the splitter 8 may be a dichroic plate.
The first embodiment is suitable for applications in which the first image and the image acquired by the image sensor are formed in the same spectral band, but with different magnifications. In this case, the splitter is a half-silvered mirror. A auxiliary optical system 7′ may be placed between the splitter 8 and the image sensor 9. The image sensor 9 acquires an image the magnification of which is higher than the magnification of the first image. Alternatively, the first optical system 10 applies an additional magnification to the image reflected by the splitter. Such an embodiment is suitable for microscopy applications as it allows two images of the same scene to be observed with different magnifications.
In a second embodiment, shown in
In a third embodiment, shown in
When the first image I1 is formed such as described with reference to one of
According to one variant, shown in
The third image is superposed on the first image I1, according to the principles of augmented reality. The viewfinder comprises a parameter-displaying display 31, configured to display the third image I3. The third image I3 is propagated by a third optical system 30 to a combiner 35, which is arranged to propagate the third image, to the eye, parallel to the first axis A1. The third image I3 is thus projected into the eye superposed on the first image I1. See
The third optical channel, which has been shown schematically in
One aspect to be taken into account is the focus of the projected images. In order for the user not to have to accommodate his vision, the first image I1 and the second image I2, and optionally the third image I3, must be displayed in the depth of field of the eye. By depth of field, what is meant is the variation in distance able to be tolerated without leading to a significant lack of sharpness. This is expressed by the following constraint on the optical systems: the distances d1, d2 and d3, defined between the pupils PS1, PS2 and PS3 (which is equal to PS1 by construction in the configuration of
The viewfinder is intended to be integrated into an observing device 2, a camera or a telescope for example. The bulk of the viewfinder must be such as to allow such an integration. It is assumed that the eye-relief parameters ER and the diameter of each exit pupil are identical for each optical channel. The volume of the viewfinder is limited by the exit dioptric interfaces 15 and 25, the diameter Φ of which is defined in (1).
e1=e2 cos(θ) (4)
The total thickness e is such that e=e1+ϕ sin(θ).
The viewfinder may be dimensioned taking into account the following parameters, the first optical system being such as described with reference to
For each optical system:
Given these values, the inventors deem that the thickness e1 may be comprised between 4 mm and 55 mm, the thickness e2 may be comprised between 4 and 70 mm, and that the total thickness e may be comprised between 7 and 85 mm, a viewfinder with these dimensions being integrable into a device such as a camera.
The tables below collate the main characteristics of the dioptric interfaces, according to the nomenclature described in Herbert Gross, Handbook of Optical Systems, Volume 4 “Survey of optical instruments”, Chapter 37.15 Eyepiece Design Data. For each surface, the material and the thickness correspond to the space between said surface and the surface of following rank.
In Table 1, S1 corresponds to the first exit pupil. The mirror is inclined to 45°.
In Table 3, S18 corresponds to the display forming the second image.
The observing device 2 may be other than a camera. It may for example be a spotting scope as shown in
According to one possibility, the peripheral device 2′ is able to move with respect to the observing device 2. It is for example located on board a vehicle, a drone for example. The observing device allows the drone to be monitored remotely, while viewing the image acquired by the peripheral image sensor located on board the drone. Thus, the first image I1 corresponds to an image showing the drone, the latter forming the scene observed by the observing device 2. The second image I2 corresponds to the image seen by the image sensor located on board the drone. Using the viewfinder 1, the user may, while looking through the viewfinder, view the two images via a simple rotation of the eye. He may thus control the drone, depending on the second image, and monitor the position of the drone in the first image.
The first image or the second image may contain information regarding the viewfinder or the device, adjustable parameters for example.
The viewfinder described above allows two images to be observed simultaneously. It may be a question of two images representative of the same observed scene, for example:
The viewfinder may be integrated into observing devices such as still cameras, video cameras, microscopes, telescopes, spotting scopes, microscopes, weapons, periscopes, and medical imaging devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21 14531 | Dec 2021 | FR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5099265 | Lee | Mar 1992 | A |
| 6650837 | Richiuso | Nov 2003 | B1 |
| 20030112355 | Bittner | Jun 2003 | A1 |
| 20030123114 | Kasai | Jul 2003 | A1 |
| 20150301334 | Getin et al. | Oct 2015 | A1 |
| 20160316147 | Bernstein | Oct 2016 | A1 |
| 20170214866 | Zhu | Jul 2017 | A1 |
| 20200259985 | Takahashi | Aug 2020 | A1 |
| Number | Date | Country |
|---|---|---|
| 2 989 791 | Oct 2013 | FR |
| Entry |
|---|
| French Preliminary Search Report and Written Opinion Issued Jul. 28, 2022 in French Application 21 14531 filed on Dec. 26, 2021 (with English Translation of Categories of Cited Documents), 9 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20230204937 A1 | Jun 2023 | US |
