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DOI: 10.22184/1993-7296.FRos.2023.17.8.632.636
The paper provides the optical channel description for digital multifunctional binoculars. The design of low-profile and lightweight television variable focus (zoom) lens and night vision and infrared lenses with internal focusing is given. The design options for the eyepiece assembly of binoculars are shown.
The paper provides the optical channel description for digital multifunctional binoculars. The design of low-profile and lightweight television variable focus (zoom) lens and night vision and infrared lenses with internal focusing is given. The design options for the eyepiece assembly of binoculars are shown.
Теги: internal focusing lens multifunctional binoculars pseudo-binocular. variable focus (zoom) lens многофункциональный бинокль объектив с внутренней фокусировкой объектив с переменным фокусным расстоянием псевдобинокуляр
Multifunctional Binoculars
I. P. Shishkin, A. P. Shkadarevich
LEMT Scientific and Technical Center of BelOMO,
Minsk, Republic of Belarus
The paper provides the optical channel description for digital multifunctional binoculars. The design of low-profile and lightweight television variable focus (zoom) lens and night vision and infrared lenses with internal focusing is given. The design options for the eyepiece assembly of binoculars are shown.
Keywords: multifunctional binoculars, variable focus (zoom) lens, internal focusing lens, pseudo-binocular.
Article received:19.09.2023
Article accepted:30.11.2023
Introduction
Digital technologies have changed the functionality of present-day observation tools. With the advent of miniaturized light sources, sensors, and displays, it has become possible to combine various channels operating in different spectral ranges. Many devices have a range tracking function and possibility to display information in the field of view. The range of magnification and operating temperatures have been increased. The devices have become more discreet and lighter.
When starting to develop multifunctional binoculars [1–2], it is necessary to determine the optimal design of the lens for each channel with due regard to a number of binocular parameters, such as magnification, field of view, resolution and observer-target range. Based on these parameters, the required lens focal length, aperture ratio and focusing range are determined. The type of the sensor and display is selected. All channels must be consistent with each other. It is well-known that the details of the observed object and its identification significantly depend on the spectral range and on the ambient light illumination. On the one part, application of one or another channel can significantly expand the capabilities of binoculars depending on the observing conditions: time of day, weather and range. On the other part, combination of 3–5 optical channels in one device leads to an increase in its dimensions and weight.
Television variable focus
(zoom) lens
The television channel of modern observation devices uses the lenses with variable focal lengths. The range of variation in the focal length between short focus (wide field of view) and long focus (narrow field of view) can reach 30–90 times. Such lenses have a comprehensive design with a large number of aspherical lenses. For the fixed instruments, where the permissible weight of the device is 5–10 kg, application of such lenses is completely justified. If the total weight of the device should not exceed 1–2 kg, it is necessary to reduce the lens dimensions, and therefore the range of focal lengths.
Figure 1 shows an example of a low-profile television lens with a variable focal length of 8–50 mm that has a fairly simple design for a zoom lens (in total 11 lenses) and is made without any aspherical surfaces. Any changes in the focal length and focusing at close distances are provided by moving two groups of lenses. The lens length is ~100mm, and its lens weight does not exceed 70 g. The lens has a large aperture ratio (F/1.25 – F/1.4) and a resolution of 80 lines/mm that allows it to be used for a sensor with a 1/2″ format (1 920 × 1 080).
Night vision lens
with internal focusing
The night vision lenses are widely used in the up-to-date observing devices. Conventionally, they are applied in combination with the electron-optical converters operating in the spectral range of 400–900 nm. This design of a night vision device has rather large dimensions, so it is difficult to use it in the multifunctional binoculars. If a digital sensor, namely a low light camera, is used as a sensing matrix, it is possible to significantly reduce the dimensions and weight of the binoculars.
The examples of lightweight and low-profile lenses that are used for low-light cameras are given in Fig. 2. Both lenses focus at close distances up to 5 m while maintaining the high image quality. In a lens with a focal length of 50 mm and a relative aperture of 1:1.4, focusing is provided by moving the last component; in a lens with a focal length of 25 mm and a relative aperture of 1:0.9, the last lens is moving. The lens resolution is 40 lines/mm, and such lenses are designed for a 1/2″ sensor (8 mm diagonal). The angular field of view of the lenses is 10° and 20°, and the their weight is no more than 70 g and 45 g.
Thermal imaging lens
with internal focusing
A view of a thermal imaging lens with internal focusing operating in the 812 µ m range is shown in Fig. 3. The achromatized thermal imaging lens [3, 4] has a triple-lens design. In this structure, the outer lenses are made of germanium, and the middle lens is made of zinc selenide. Internal focusing is achieved by moving the middle lens. The weight of lenses does not exceed 30 g, and its length is 65 mm. The main specifications of the lenses are shown in the table.
Pseudo-binocular
Observation of distant objects with two eyes is more comfortable and natural for a person. For this reason, many manufacturers of telescopic devices use a binocular or pseudo-binocular design in their work. The pseudobinocular circuit is more discreet and lightweight, therefore it is preferred when developing the up-to-date digital devices. Figure 4a shows a well-known layout of a pseudo-binocular for a night vision device. Due to the use of aspherics, the number of lenses is reduced as much as possible and thus the design is significantly simplified. Figure 4b shows a more discreet option of a pseudobinocular with an original arrangement of prisms and a beam splitter (splitter). Both options can be applied with an apparent magnification of 10–15x and an exit pupil of 5–6 mm, its distortion does not exceed 1–2% with a field of view of 40° behind the eyepiece.
The interpupillary distance can vary within 58–72 mm due to the movement of components located within a parallel path of the rays (in the 1st option, this is the space between the lenses and the prism, in the 2nd option, this is achieved due to the right channel movement of relative to the splitter).
Conclusion
The solutions given in the article can be used not only for the development of multifunctional binoculars, but also for the creation of a wide range of optical devices when the light weight and compactness are priorities.
About authors
Shishkin Igor Petrovich, Candidate of Technical Sciences, shipoflens@mail.ru, RTC “LEMT” BelOMO, Minsk, Republic of Belarus.
ORCID ID: 0000-0002-4592-1060
Shkadarevich Alexey Petrovich, Doctor of Technical Sciences, RTC “LEMT” BelOMO, Minsk, Republic of Belarus.
Contribution by the members
of the team of authors
The article was prepared on the basis of many years of work by all members of the team of authors. Development and research are carried out at the expense of RTC “LEMT” BELOMO.
Conflict of interest
The authors claim that they have no conflict of interest.
I. P. Shishkin, A. P. Shkadarevich
LEMT Scientific and Technical Center of BelOMO,
Minsk, Republic of Belarus
The paper provides the optical channel description for digital multifunctional binoculars. The design of low-profile and lightweight television variable focus (zoom) lens and night vision and infrared lenses with internal focusing is given. The design options for the eyepiece assembly of binoculars are shown.
Keywords: multifunctional binoculars, variable focus (zoom) lens, internal focusing lens, pseudo-binocular.
Article received:19.09.2023
Article accepted:30.11.2023
Introduction
Digital technologies have changed the functionality of present-day observation tools. With the advent of miniaturized light sources, sensors, and displays, it has become possible to combine various channels operating in different spectral ranges. Many devices have a range tracking function and possibility to display information in the field of view. The range of magnification and operating temperatures have been increased. The devices have become more discreet and lighter.
When starting to develop multifunctional binoculars [1–2], it is necessary to determine the optimal design of the lens for each channel with due regard to a number of binocular parameters, such as magnification, field of view, resolution and observer-target range. Based on these parameters, the required lens focal length, aperture ratio and focusing range are determined. The type of the sensor and display is selected. All channels must be consistent with each other. It is well-known that the details of the observed object and its identification significantly depend on the spectral range and on the ambient light illumination. On the one part, application of one or another channel can significantly expand the capabilities of binoculars depending on the observing conditions: time of day, weather and range. On the other part, combination of 3–5 optical channels in one device leads to an increase in its dimensions and weight.
Television variable focus
(zoom) lens
The television channel of modern observation devices uses the lenses with variable focal lengths. The range of variation in the focal length between short focus (wide field of view) and long focus (narrow field of view) can reach 30–90 times. Such lenses have a comprehensive design with a large number of aspherical lenses. For the fixed instruments, where the permissible weight of the device is 5–10 kg, application of such lenses is completely justified. If the total weight of the device should not exceed 1–2 kg, it is necessary to reduce the lens dimensions, and therefore the range of focal lengths.
Figure 1 shows an example of a low-profile television lens with a variable focal length of 8–50 mm that has a fairly simple design for a zoom lens (in total 11 lenses) and is made without any aspherical surfaces. Any changes in the focal length and focusing at close distances are provided by moving two groups of lenses. The lens length is ~100mm, and its lens weight does not exceed 70 g. The lens has a large aperture ratio (F/1.25 – F/1.4) and a resolution of 80 lines/mm that allows it to be used for a sensor with a 1/2″ format (1 920 × 1 080).
Night vision lens
with internal focusing
The night vision lenses are widely used in the up-to-date observing devices. Conventionally, they are applied in combination with the electron-optical converters operating in the spectral range of 400–900 nm. This design of a night vision device has rather large dimensions, so it is difficult to use it in the multifunctional binoculars. If a digital sensor, namely a low light camera, is used as a sensing matrix, it is possible to significantly reduce the dimensions and weight of the binoculars.
The examples of lightweight and low-profile lenses that are used for low-light cameras are given in Fig. 2. Both lenses focus at close distances up to 5 m while maintaining the high image quality. In a lens with a focal length of 50 mm and a relative aperture of 1:1.4, focusing is provided by moving the last component; in a lens with a focal length of 25 mm and a relative aperture of 1:0.9, the last lens is moving. The lens resolution is 40 lines/mm, and such lenses are designed for a 1/2″ sensor (8 mm diagonal). The angular field of view of the lenses is 10° and 20°, and the their weight is no more than 70 g and 45 g.
Thermal imaging lens
with internal focusing
A view of a thermal imaging lens with internal focusing operating in the 812 µ m range is shown in Fig. 3. The achromatized thermal imaging lens [3, 4] has a triple-lens design. In this structure, the outer lenses are made of germanium, and the middle lens is made of zinc selenide. Internal focusing is achieved by moving the middle lens. The weight of lenses does not exceed 30 g, and its length is 65 mm. The main specifications of the lenses are shown in the table.
Pseudo-binocular
Observation of distant objects with two eyes is more comfortable and natural for a person. For this reason, many manufacturers of telescopic devices use a binocular or pseudo-binocular design in their work. The pseudobinocular circuit is more discreet and lightweight, therefore it is preferred when developing the up-to-date digital devices. Figure 4a shows a well-known layout of a pseudo-binocular for a night vision device. Due to the use of aspherics, the number of lenses is reduced as much as possible and thus the design is significantly simplified. Figure 4b shows a more discreet option of a pseudobinocular with an original arrangement of prisms and a beam splitter (splitter). Both options can be applied with an apparent magnification of 10–15x and an exit pupil of 5–6 mm, its distortion does not exceed 1–2% with a field of view of 40° behind the eyepiece.
The interpupillary distance can vary within 58–72 mm due to the movement of components located within a parallel path of the rays (in the 1st option, this is the space between the lenses and the prism, in the 2nd option, this is achieved due to the right channel movement of relative to the splitter).
Conclusion
The solutions given in the article can be used not only for the development of multifunctional binoculars, but also for the creation of a wide range of optical devices when the light weight and compactness are priorities.
About authors
Shishkin Igor Petrovich, Candidate of Technical Sciences, shipoflens@mail.ru, RTC “LEMT” BelOMO, Minsk, Republic of Belarus.
ORCID ID: 0000-0002-4592-1060
Shkadarevich Alexey Petrovich, Doctor of Technical Sciences, RTC “LEMT” BelOMO, Minsk, Republic of Belarus.
Contribution by the members
of the team of authors
The article was prepared on the basis of many years of work by all members of the team of authors. Development and research are carried out at the expense of RTC “LEMT” BELOMO.
Conflict of interest
The authors claim that they have no conflict of interest.
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