rus
Issue #6/2021
P. S. Zavyalov, E. V. Vlasov, A. V. Soldatenko, M. A. Zavyalova, V. S. Bartosh
Development of Optical Schemes for Formation of a Comfortable Visual Simulation in The Field of Simulators Building
Development of Optical Schemes for Formation of a Comfortable Visual Simulation in The Field of Simulators Building
DOI: 10.22184/1993-7296.FRos.2021.15.6.526.539
The article discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation. The requirements for the quality of the generated image when working with an observer have been established. Two options for constructing projection optical systems are presented that provide a sufficiently wide field of view for a stationary observer.
The article discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation. The requirements for the quality of the generated image when working with an observer have been established. Two options for constructing projection optical systems are presented that provide a sufficiently wide field of view for a stationary observer.
Теги: distortion field of view projection systems virtual simulators visual simulation визуализация обстановки виртуальные тренажеры дисторсия проекционные системы угол поля зрения
Development of Optical Schemes for Formation of a Comfortable Visual Simulation in The Field of Simulators Building
P. S. Zavyalov , E. V. Vlasov, A. V. Soldatenko, M. A. Zavyalova, V. S. Bartosh
Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of Russian Academy of Sciences
Institute of Automation and Electrometry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia
The article discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation. The requirements for the quality of the generated image when working with an observer have been established. Two options for constructing projection optical systems are presented that provide a sufficiently wide field of view for a stationary observer.
Keywords: visual simulation, virtual simulators, projection systems, field of view, distortion
Received on: 12.08.2021
Accepted on: 08.09.2021
Introduction
The technical and scientific literature contains a large amount of information on visual simulation devices that are used in the field of entertainment, architectural and industrial design, simulators and other areas. In this paper, a narrower task of visualizing information in viewing windows or portholes is considered. Such devices are used, e. g., in simulators of spaceships, underwater vehicles, special vehicles, etc., where the position of the observer is very limited, on the other hand, it is impossible or prohibited to use visual simulation on the human head (special glasses, helmets, eyepieces, etc. etc.). These features limit the choice of designs and optical design of imaging devices. One of the critical parameters for an imaging device is the size of the field of view. The wider it is, the greater the «presence effect» will be formed in the simulator.
Basic principles of construction of imaging devices
According to the principle of constructing an optical scheme, the following two groups of methods can be distinguished: screen methods, where there is no optical scheme between the observer and the image source, and projection methods, in which elements with optical power (mirrors, lenses) are used in the formation of a visual simulation for the observer.
Screen methods can be classified according to the source of the image, which can be either a light-scattering or translucent screen illuminated by a projector, or one or more displays (monitors).
To simulate a visual simulation with a wide field of view (up to 360°), screens of various shapes (flat, spherical, toroidal) are used, which are illuminated by several LCD or DLP projectors. In this case, the fields of the projectors have to be sufficiently accurately calibrated [1] to minimize the effects observed in the area of overlapping zones.
When using displays, it is also possible to obtain sufficiently large fields of view by combining them with each other. However, due to the design features – the presence of a frame in most displays – joints will be visible in the formed picture.
All of the above screen methods have certain disadvantages. First, the visual simulation is created at a certain limited distance. This prevents the stimuli of the eye accommodation from being activated. The operator sees that the picture is somewhere close. Therefore, when synthesizing the far zone, they try to place the screens as far as possible from the operator (from 2 to 10 m), where this visual discomfort is no longer felt. Secondly, when the screen / display is located close, the parallax effect will not be observed, when, when the observer’s head is displaced, errors will occur in determining the spatial location of close and distant objects. In some cases, such a situation can be quite critical, since the trainees have a wrong idea of how to drive a vehicle. In some situations, this can lead to serious consequences. On-screen methods are widely used in flight simulators, where the entire synthesized environment is usually located in the far zone (at infinity), and the observer’s ability to move is severely limited by a cramped cockpit [2–8].
In projection methods, an optical system is installed between the image source (screen, display, slide, template, etc.), which creates, as a rule, a virtual image at a finite or infinite distance from the operator [9–11]. Moreover, in such systems, it is possible to change the apparent range to the synthesized pattern by changing the distance between the optical system and the image source. It is also possible to create several plans (near and far) by combining several image sources using prisms and semitransparent mirrors. Concave mirrors (usually of a spherical shape) are widely used as the main optical element for collimation of radiation in simulation equipment. In this case, the image source is placed in the focus of the spherical mirror: F = R / 2. The main problem when using this option is that the image source is in this case between the mirror and the observer (Fig. 1a). For wide-angle schemes (the field of view is more than 30°), this presents a significant problem; therefore, two ways are used here: either an intermediate image is projected into this area through a semitransparent mirror (Fig.1b), or an off-axis optical scheme is made (Fig.1c).
This option for constructing a projection optical system can provide a fairly wide field of view (within 30° – 60°). When a toroidal mirror is used instead of a spherical mirror, in the focus of which a toroidal transmission screen is also installed, a wide panoramic view of up to 180° can be achieved, but the same 30° – 60° will be at the other coordinate [9–11].
Instead of a mirror optical scheme, lens optical schemes are also used. In this case, if the screen is installed in the focal plane of some lens, the observer sees an object infinitely distant from him. In this case, the field of view can reach rather large values (up to 90–120°). But at the same time, the diameters of the optical elements also increase.
With high requirements for image quality to correct aberrations, it is necessary to use multilens optical circuits made of different types of glasses. Therefore, lens schemes are more often used for monocular observation. This circumstance explains the fact that the most widespread are mirror projection schemes, since large format mirrors are much easier to manufacture, and the mirrors themselves do not introduce chromatic aberrations. However, at the same time, off-axis wide-angle mirror schemes introduce significant distortions (astigmatism and coma). Therefore, when using them, it is required to analyze the quality of the formed image and find a balance between the magnitude of the field of view and the values of aberrations.
Requirements for the quality
of the generated image
Requirements for image quality are very diverse and depend on the problem being solved with the help of the optical system. A complete correction of all aberrations cannot be obtained even in an arbitrarily complex system. Therefore, residual aberrations are allowed, their values are determined by the purpose of the system and the image receiver.
In telescopic systems (distant object – distant image), working with the eye, good image quality should be in the center of the field, and deterioration of the image quality is allowed at the edge of the field, since the image in question can always be brought to the center of the field. Since the eye is the image receiver, the allowable aberration values should be less than or commensurate with the eye resolution. Table shows the allowable telescope aberration values.
The given values were obtained from long-term practical observations [12–15]. They are convenient to use when assessing the acceptable quality of systems working with an image receiver such as the eye.
When evaluating off-axis aberrations of telescopes and, consequently, eyepieces, the operating conditions must be taken into account. Thus, in binoculars and telescopes held in hands, a person, seeing the edges of the image field due to peripheral vision and noticing some movement there, turns his head along with the binoculars and transfers the «suspicious» area to the center. In such cases, the edges of the eyepiece image field are perceived by peripheral vision and may have large aberrations. In devices placed stationary, e. g., in tank panoramas, stereoscopic tubes, etc., transferring the extreme zones of the image field to the center takes a significant amount of time, so the observer is forced to consider the edges of the image field by turning his eye.
In photographic lenses (distant object – near image), the requirements for image quality are very diverse and largely depend on the operating spectral range, the image receiver and the purpose of the system. Image quality requirements may include: resolution in lines / mm in the center of the field and at the edge, frequency-contrast characteristic (FCC) with an indication of the frequency and the required contrast. In infrared systems, the diameter of the scattering circle with a given concentration of energy in it can be set.
In projection systems (near subject – near image), if they are calculated in the reverse path of the rays, the requirements for image quality are approximately the same as in photographic systems.
The image quality in the plane of the screen can be estimated by the angle at which the observer sees the scattering circle. If the angle is 1’ – 2’, then the image quality can be considered satisfactory.
Thus, from the above requirements for visual devices, it can be seen that the main criterion for the quality of an optical system that forms a visual simulation is the resolution over the entire field of view, which should reach the resolution limit of the human eye 1’ – 2’. In this case, for the imager, as a stationary system, it is impossible to impose different requirements for the resolution at the edge and in the center of the field of view. The resolution across the entire field should tend to 2’.
Distortion for visual devices is usually limited to 2–5%, at which a person does not notice significant geometric distortions. For the above variants of optical schemes of systems for synthesizing a visual simulation, the distortion usually significantly exceeds the specified threshold. In this case, it is necessary to compensate for distortion distortions by forming an appropriate digital visual model.
Mirror projection system
As the first variant of image formation, an optical scheme with an off-axis screen arrangement was considered, shown in Fig. 1c. There, an inclined concave spherical mirror is used as the main element, in the focal region of which a transmissive spherical screen is installed. An LCD or DLP projector is used as the image source. In this case, it is necessary to use a lens for the projector, which allows you to build an image of a small size (~ 0.5 m).
When calculating such an optical scheme, dimensional restrictions on the location of all optical elements are of decisive importance. As a result, in the software package for calculating optical systems Zemax Optical Studio [16], a variant of the scheme was obtained, shown in Fig. 2.
The obtained main characteristics of the optical scheme: the diameter of the illuminator is 250 mm, the angle of the field of view: ± 26°, the overall size of the large spherical mirror ∅1100 mm, the radius of curvature of the spherical mirror R = 1400 mm, the overall size of the transmissive screen ∅480 mm, the distortion: 18.5% (asymmetric). The image quality in this optical scheme is determined exclusively by the spherical mirror. There are no chromatic aberrations. The decisive role for resolution is played by astigmatism, which increases with an increase in the angle of incidence of the rays on the surface of the mirror. Therefore, when calculating this option, it is necessary to reduce this angle. The scattering spots of the calculated mirror projection system are shown in Fig. 3.
It should be noted that in this variant there is no strong dependence on the displacement of the observer’s eye. When the observer is displaced to the side relative to the optical axis, the resolution deteriorates slightly (see Fig. 4).
It can be seen from Fig. 4 that this optical scheme has a rather low resolution (2’- 7’), which also strongly depends on the direction of view. The edge of the mirror farthest from the porthole will appear blurred. The type of distortion is shown in Fig. 5.
The main advantages of such an imaging device are the relative simplicity of the design and the possibility of synthesizing the visual simulation at a distance from 2 m to ∞. At the same time, the following disadvantages should be noted: limited field of view (up to ± 26°), general asymmetry of the picture in terms of quality, astigmatism at one of the edges leads to a drop in resolution (up to 6′ – 8′), large asymmetric distortion (18.5%).
Lens projection system
A lens optical scheme was considered as an implementation of the imaging device. In this case, a lens assembly is installed in front of the illuminator, in the focus of which is a light-scattering screen illuminated by one or more projectors.
When calculating this optical scheme, the characteristics of the lens objective are of decisive importance for the image quality. To minimize chromatism, at least two grades of glass should be used.
This version of the optical scheme was calculated using the Zemax Optical Studio software package [16]. As the main optimization criterion, the minimum of the geometric circle of scattering for the observer behind the window was used. Also, additional criteria were the maximum value of the field of view, the dimensions and mass of the optical elements, and the magnitude of the distortion.
As a result of the calculation, a variant of the optical scheme was obtained, shown in Fig. 6.
The following main characteristics of the optical scheme were obtained: field of view angle ± 50°, overall size of the projection screen ∅ 5 m, distance to the screen 2.7 m, radius of curvature of the projection screen ∅12 m, size of the largest lens 320 mm, number of lenses 2 pcs, brand glasses: LAK33, SF15 (Schott catalog), distortion no more than 22% (symmetrical). The image quality for the eye located on the optical axis can be considered almost ideal. Geometric distortion and chromatic aberration are much less than the diffraction limit (scattering point diagrams are shown in Fig. 7a). When the observer’s eye is displaced, some deterioration in image quality occurs due to the chromatism of magnification (see Fig. 7b).
Since this version of the optical scheme has a large margin of image quality, if necessary, you can abandon the use of a spherical screen, due to the complexity of manufacturing, and use a flat one. In this case, the resolution will decrease by only 17%. In addition, the image resolution can be improved by 22% by using an aspherical surface on the first lens.
To illustrate the quality of the formed picture, a series of graphs were calculated, shown in Fig. 8 and showing the dependence of the resolution on the displacement of the observer’s eye (R hl) for different angles of view (α). The graphs of field curvature and distortion are shown in Fig. 9. Figure 8 shows that this optical scheme has good resolution characteristics (from 1’ to 4’) with a large field of view (up to 100°). For optimal use of the capabilities of the optical system with this ratio of resolution and field of view, it is necessary to use at least a projector with a resolution of 8K UltraHD (7680 × 4320), which will allow synthesizing a visual simulation with a resolution of 0.8′ – 1.4′. When using two projectors with 4K UltraHD (3840 × 2160) resolution, the resolution will be in the order of 1.4’- 1.6’.
When implementing this scheme, it is possible to form a visual simulation at a distance from 2 m to ∞; provide the maximum viewing angle (100°), close to human vision (130° – 160°); have a high resolution over the entire field of view (1′ – 3′), close to the resolution of the human eye. There is also a lower sensitivity to displacement of the observer’s head compared to the first scheme. The disadvantages include large symmetric distortion (22%), which can be minimized by software, and large overall dimensions of the stand.
Conclusion
The paper discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation in viewing windows or portholes. The basic requirements for the quality of the generated image when working with an observer are presented. Two options for the construction of projection optical systems providing a sufficiently wide field of view are presented. In the first version, a concave spherical mirror is used in the focus of which a translucent spherical screen is installed. This option is quite simple to implement, but it has been shown that there are certain disadvantages: a limited field of view (up to ± 26°) and a general asymmetry of the picture in terms of image quality. In the second lens variant, significantly better image quality characteristics are achieved with a larger field of view (up to ± 50°).
The results obtained can be used in modern simulation equipment, since they make it possible to create devices for the synthesis of a visual simulation that forms an environment for human eyes that is close enough to natural, which undoubtedly increases the visual comfort during the work of operators.
AUTHORS
Petr Sergeevich Zavyalov, Cand. Of Technical Sciences, Director of the Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; zavyalov@tdisie.nsc.ru; Novosibirsk, Russia.
Evgeny Vladimirovich Vlasov, Researcher, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; vlasov@tdisie.nsc.ru; Novosibirsk, Russia.
Alexey Vladimirovich Soldatenko, Designer, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; tok9_11@mail.ru; Novosibirsk, Russia.
Marina Andreevna Zavyalova, Cand. Of Technical Sciences, Researcher, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; mzav@tdisie.nsc.ru; Novosibirsk, Russia.
Vasily Stanislavovich Bartosh, Lead Engineer, Institute of Automation and Electrometry, Siberian Branch of RAS, vas@sl.iae.nsk.su; Novosibirsk, Russia.
P. S. Zavyalov , E. V. Vlasov, A. V. Soldatenko, M. A. Zavyalova, V. S. Bartosh
Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of Russian Academy of Sciences
Institute of Automation and Electrometry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia
The article discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation. The requirements for the quality of the generated image when working with an observer have been established. Two options for constructing projection optical systems are presented that provide a sufficiently wide field of view for a stationary observer.
Keywords: visual simulation, virtual simulators, projection systems, field of view, distortion
Received on: 12.08.2021
Accepted on: 08.09.2021
Introduction
The technical and scientific literature contains a large amount of information on visual simulation devices that are used in the field of entertainment, architectural and industrial design, simulators and other areas. In this paper, a narrower task of visualizing information in viewing windows or portholes is considered. Such devices are used, e. g., in simulators of spaceships, underwater vehicles, special vehicles, etc., where the position of the observer is very limited, on the other hand, it is impossible or prohibited to use visual simulation on the human head (special glasses, helmets, eyepieces, etc. etc.). These features limit the choice of designs and optical design of imaging devices. One of the critical parameters for an imaging device is the size of the field of view. The wider it is, the greater the «presence effect» will be formed in the simulator.
Basic principles of construction of imaging devices
According to the principle of constructing an optical scheme, the following two groups of methods can be distinguished: screen methods, where there is no optical scheme between the observer and the image source, and projection methods, in which elements with optical power (mirrors, lenses) are used in the formation of a visual simulation for the observer.
Screen methods can be classified according to the source of the image, which can be either a light-scattering or translucent screen illuminated by a projector, or one or more displays (monitors).
To simulate a visual simulation with a wide field of view (up to 360°), screens of various shapes (flat, spherical, toroidal) are used, which are illuminated by several LCD or DLP projectors. In this case, the fields of the projectors have to be sufficiently accurately calibrated [1] to minimize the effects observed in the area of overlapping zones.
When using displays, it is also possible to obtain sufficiently large fields of view by combining them with each other. However, due to the design features – the presence of a frame in most displays – joints will be visible in the formed picture.
All of the above screen methods have certain disadvantages. First, the visual simulation is created at a certain limited distance. This prevents the stimuli of the eye accommodation from being activated. The operator sees that the picture is somewhere close. Therefore, when synthesizing the far zone, they try to place the screens as far as possible from the operator (from 2 to 10 m), where this visual discomfort is no longer felt. Secondly, when the screen / display is located close, the parallax effect will not be observed, when, when the observer’s head is displaced, errors will occur in determining the spatial location of close and distant objects. In some cases, such a situation can be quite critical, since the trainees have a wrong idea of how to drive a vehicle. In some situations, this can lead to serious consequences. On-screen methods are widely used in flight simulators, where the entire synthesized environment is usually located in the far zone (at infinity), and the observer’s ability to move is severely limited by a cramped cockpit [2–8].
In projection methods, an optical system is installed between the image source (screen, display, slide, template, etc.), which creates, as a rule, a virtual image at a finite or infinite distance from the operator [9–11]. Moreover, in such systems, it is possible to change the apparent range to the synthesized pattern by changing the distance between the optical system and the image source. It is also possible to create several plans (near and far) by combining several image sources using prisms and semitransparent mirrors. Concave mirrors (usually of a spherical shape) are widely used as the main optical element for collimation of radiation in simulation equipment. In this case, the image source is placed in the focus of the spherical mirror: F = R / 2. The main problem when using this option is that the image source is in this case between the mirror and the observer (Fig. 1a). For wide-angle schemes (the field of view is more than 30°), this presents a significant problem; therefore, two ways are used here: either an intermediate image is projected into this area through a semitransparent mirror (Fig.1b), or an off-axis optical scheme is made (Fig.1c).
This option for constructing a projection optical system can provide a fairly wide field of view (within 30° – 60°). When a toroidal mirror is used instead of a spherical mirror, in the focus of which a toroidal transmission screen is also installed, a wide panoramic view of up to 180° can be achieved, but the same 30° – 60° will be at the other coordinate [9–11].
Instead of a mirror optical scheme, lens optical schemes are also used. In this case, if the screen is installed in the focal plane of some lens, the observer sees an object infinitely distant from him. In this case, the field of view can reach rather large values (up to 90–120°). But at the same time, the diameters of the optical elements also increase.
With high requirements for image quality to correct aberrations, it is necessary to use multilens optical circuits made of different types of glasses. Therefore, lens schemes are more often used for monocular observation. This circumstance explains the fact that the most widespread are mirror projection schemes, since large format mirrors are much easier to manufacture, and the mirrors themselves do not introduce chromatic aberrations. However, at the same time, off-axis wide-angle mirror schemes introduce significant distortions (astigmatism and coma). Therefore, when using them, it is required to analyze the quality of the formed image and find a balance between the magnitude of the field of view and the values of aberrations.
Requirements for the quality
of the generated image
Requirements for image quality are very diverse and depend on the problem being solved with the help of the optical system. A complete correction of all aberrations cannot be obtained even in an arbitrarily complex system. Therefore, residual aberrations are allowed, their values are determined by the purpose of the system and the image receiver.
In telescopic systems (distant object – distant image), working with the eye, good image quality should be in the center of the field, and deterioration of the image quality is allowed at the edge of the field, since the image in question can always be brought to the center of the field. Since the eye is the image receiver, the allowable aberration values should be less than or commensurate with the eye resolution. Table shows the allowable telescope aberration values.
The given values were obtained from long-term practical observations [12–15]. They are convenient to use when assessing the acceptable quality of systems working with an image receiver such as the eye.
When evaluating off-axis aberrations of telescopes and, consequently, eyepieces, the operating conditions must be taken into account. Thus, in binoculars and telescopes held in hands, a person, seeing the edges of the image field due to peripheral vision and noticing some movement there, turns his head along with the binoculars and transfers the «suspicious» area to the center. In such cases, the edges of the eyepiece image field are perceived by peripheral vision and may have large aberrations. In devices placed stationary, e. g., in tank panoramas, stereoscopic tubes, etc., transferring the extreme zones of the image field to the center takes a significant amount of time, so the observer is forced to consider the edges of the image field by turning his eye.
In photographic lenses (distant object – near image), the requirements for image quality are very diverse and largely depend on the operating spectral range, the image receiver and the purpose of the system. Image quality requirements may include: resolution in lines / mm in the center of the field and at the edge, frequency-contrast characteristic (FCC) with an indication of the frequency and the required contrast. In infrared systems, the diameter of the scattering circle with a given concentration of energy in it can be set.
In projection systems (near subject – near image), if they are calculated in the reverse path of the rays, the requirements for image quality are approximately the same as in photographic systems.
The image quality in the plane of the screen can be estimated by the angle at which the observer sees the scattering circle. If the angle is 1’ – 2’, then the image quality can be considered satisfactory.
Thus, from the above requirements for visual devices, it can be seen that the main criterion for the quality of an optical system that forms a visual simulation is the resolution over the entire field of view, which should reach the resolution limit of the human eye 1’ – 2’. In this case, for the imager, as a stationary system, it is impossible to impose different requirements for the resolution at the edge and in the center of the field of view. The resolution across the entire field should tend to 2’.
Distortion for visual devices is usually limited to 2–5%, at which a person does not notice significant geometric distortions. For the above variants of optical schemes of systems for synthesizing a visual simulation, the distortion usually significantly exceeds the specified threshold. In this case, it is necessary to compensate for distortion distortions by forming an appropriate digital visual model.
Mirror projection system
As the first variant of image formation, an optical scheme with an off-axis screen arrangement was considered, shown in Fig. 1c. There, an inclined concave spherical mirror is used as the main element, in the focal region of which a transmissive spherical screen is installed. An LCD or DLP projector is used as the image source. In this case, it is necessary to use a lens for the projector, which allows you to build an image of a small size (~ 0.5 m).
When calculating such an optical scheme, dimensional restrictions on the location of all optical elements are of decisive importance. As a result, in the software package for calculating optical systems Zemax Optical Studio [16], a variant of the scheme was obtained, shown in Fig. 2.
The obtained main characteristics of the optical scheme: the diameter of the illuminator is 250 mm, the angle of the field of view: ± 26°, the overall size of the large spherical mirror ∅1100 mm, the radius of curvature of the spherical mirror R = 1400 mm, the overall size of the transmissive screen ∅480 mm, the distortion: 18.5% (asymmetric). The image quality in this optical scheme is determined exclusively by the spherical mirror. There are no chromatic aberrations. The decisive role for resolution is played by astigmatism, which increases with an increase in the angle of incidence of the rays on the surface of the mirror. Therefore, when calculating this option, it is necessary to reduce this angle. The scattering spots of the calculated mirror projection system are shown in Fig. 3.
It should be noted that in this variant there is no strong dependence on the displacement of the observer’s eye. When the observer is displaced to the side relative to the optical axis, the resolution deteriorates slightly (see Fig. 4).
It can be seen from Fig. 4 that this optical scheme has a rather low resolution (2’- 7’), which also strongly depends on the direction of view. The edge of the mirror farthest from the porthole will appear blurred. The type of distortion is shown in Fig. 5.
The main advantages of such an imaging device are the relative simplicity of the design and the possibility of synthesizing the visual simulation at a distance from 2 m to ∞. At the same time, the following disadvantages should be noted: limited field of view (up to ± 26°), general asymmetry of the picture in terms of quality, astigmatism at one of the edges leads to a drop in resolution (up to 6′ – 8′), large asymmetric distortion (18.5%).
Lens projection system
A lens optical scheme was considered as an implementation of the imaging device. In this case, a lens assembly is installed in front of the illuminator, in the focus of which is a light-scattering screen illuminated by one or more projectors.
When calculating this optical scheme, the characteristics of the lens objective are of decisive importance for the image quality. To minimize chromatism, at least two grades of glass should be used.
This version of the optical scheme was calculated using the Zemax Optical Studio software package [16]. As the main optimization criterion, the minimum of the geometric circle of scattering for the observer behind the window was used. Also, additional criteria were the maximum value of the field of view, the dimensions and mass of the optical elements, and the magnitude of the distortion.
As a result of the calculation, a variant of the optical scheme was obtained, shown in Fig. 6.
The following main characteristics of the optical scheme were obtained: field of view angle ± 50°, overall size of the projection screen ∅ 5 m, distance to the screen 2.7 m, radius of curvature of the projection screen ∅12 m, size of the largest lens 320 mm, number of lenses 2 pcs, brand glasses: LAK33, SF15 (Schott catalog), distortion no more than 22% (symmetrical). The image quality for the eye located on the optical axis can be considered almost ideal. Geometric distortion and chromatic aberration are much less than the diffraction limit (scattering point diagrams are shown in Fig. 7a). When the observer’s eye is displaced, some deterioration in image quality occurs due to the chromatism of magnification (see Fig. 7b).
Since this version of the optical scheme has a large margin of image quality, if necessary, you can abandon the use of a spherical screen, due to the complexity of manufacturing, and use a flat one. In this case, the resolution will decrease by only 17%. In addition, the image resolution can be improved by 22% by using an aspherical surface on the first lens.
To illustrate the quality of the formed picture, a series of graphs were calculated, shown in Fig. 8 and showing the dependence of the resolution on the displacement of the observer’s eye (R hl) for different angles of view (α). The graphs of field curvature and distortion are shown in Fig. 9. Figure 8 shows that this optical scheme has good resolution characteristics (from 1’ to 4’) with a large field of view (up to 100°). For optimal use of the capabilities of the optical system with this ratio of resolution and field of view, it is necessary to use at least a projector with a resolution of 8K UltraHD (7680 × 4320), which will allow synthesizing a visual simulation with a resolution of 0.8′ – 1.4′. When using two projectors with 4K UltraHD (3840 × 2160) resolution, the resolution will be in the order of 1.4’- 1.6’.
When implementing this scheme, it is possible to form a visual simulation at a distance from 2 m to ∞; provide the maximum viewing angle (100°), close to human vision (130° – 160°); have a high resolution over the entire field of view (1′ – 3′), close to the resolution of the human eye. There is also a lower sensitivity to displacement of the observer’s head compared to the first scheme. The disadvantages include large symmetric distortion (22%), which can be minimized by software, and large overall dimensions of the stand.
Conclusion
The paper discusses the basic principles, advantages and disadvantages of imaging devices for visual simulation in viewing windows or portholes. The basic requirements for the quality of the generated image when working with an observer are presented. Two options for the construction of projection optical systems providing a sufficiently wide field of view are presented. In the first version, a concave spherical mirror is used in the focus of which a translucent spherical screen is installed. This option is quite simple to implement, but it has been shown that there are certain disadvantages: a limited field of view (up to ± 26°) and a general asymmetry of the picture in terms of image quality. In the second lens variant, significantly better image quality characteristics are achieved with a larger field of view (up to ± 50°).
The results obtained can be used in modern simulation equipment, since they make it possible to create devices for the synthesis of a visual simulation that forms an environment for human eyes that is close enough to natural, which undoubtedly increases the visual comfort during the work of operators.
AUTHORS
Petr Sergeevich Zavyalov, Cand. Of Technical Sciences, Director of the Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; zavyalov@tdisie.nsc.ru; Novosibirsk, Russia.
Evgeny Vladimirovich Vlasov, Researcher, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; vlasov@tdisie.nsc.ru; Novosibirsk, Russia.
Alexey Vladimirovich Soldatenko, Designer, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; tok9_11@mail.ru; Novosibirsk, Russia.
Marina Andreevna Zavyalova, Cand. Of Technical Sciences, Researcher, Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of RAS; mzav@tdisie.nsc.ru; Novosibirsk, Russia.
Vasily Stanislavovich Bartosh, Lead Engineer, Institute of Automation and Electrometry, Siberian Branch of RAS, vas@sl.iae.nsk.su; Novosibirsk, Russia.
Readers feedback
