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DOI: 10.22184/1993-7296.FRos.2025.19.3.224.231
The article describes the design of inner focusing lenses. Lenses can be used in surveillance devices, night vision devices, for application in machine vision systems, in photography and other fields. Wide-angle lens with a focal length of 16 mm and an aperture of F / 1.8, fast lens with a focal length of 26 mm and an aperture of F / 1.2, lens with a focal length of 50 mm and an aperture of F / 1.4, lens with a focal length of 100 mm and an aperture of F / 2.8, telephoto lens with a focal length of 200 mm and an aperture of F / 4, as well as for comparison a lens with a variable focal length of 10–300 mm and an aperture of F / 1.6–4.5.
The article describes the design of inner focusing lenses. Lenses can be used in surveillance devices, night vision devices, for application in machine vision systems, in photography and other fields. Wide-angle lens with a focal length of 16 mm and an aperture of F / 1.8, fast lens with a focal length of 26 mm and an aperture of F / 1.2, lens with a focal length of 50 mm and an aperture of F / 1.4, lens with a focal length of 100 mm and an aperture of F / 2.8, telephoto lens with a focal length of 200 mm and an aperture of F / 4, as well as for comparison a lens with a variable focal length of 10–300 mm and an aperture of F / 1.6–4.5.
Теги: inner focusing lens machine vision night vision devices photography surveillance devices television lens машинное зрение объективы c внутренней фокусировкой приборы наблюдения приборы ночного видения фотография
Inner Focusing Lens
I. P. Shishkin, A. P. Shkadarevich
NTC “LEMT” BeloMO, Minsk, Republic of Belarus
The article describes the design of inner focusing lenses. Lenses can be used in surveillance devices, night vision devices, for application in machine vision systems, in photography and other fields. Wide-angle lens with a focal length of 16 mm and an aperture of F / 1.8, fast lens with a focal length of 26 mm and an aperture of F / 1.2, lens with a focal length of 50 mm and an aperture of F / 1.4, lens with a focal length of 100 mm and an aperture of F / 2.8, telephoto lens with a focal length of 200 mm and an aperture of F / 4, as well as for comparison a lens with a variable focal length of 10–300 mm and an aperture of F / 1.6–4.5.
Keywords: inner focusing lens, television lens, surveillance devices, night vision devices, machine vision, photography
Article received: 01.04.2025
Article accepted: 21.04.2025
Introduction
Television lenses with variable focal length are actively used in modern surveillance devices. The range of focal lengths can vary widely (10–60 times) depending on device applications. The use of zoom lenses in observation devices is associated with the perform of two functions: viewing the observed space when using a wide field of view and maximizing the approach of the object when using a narrow field of view.
Since zoom lenses tend to have acceptable image quality over the entire range of focal lengths, it is not possible to obtain the maximum resolution of an object in a narrow field. An alternative solution for obtaining maximum image quality (close to theoretical limit) is fixed-focus lenses.
A distinctive feature of the presented lenses, which have acceptable image quality, is the simplicity of the design – the minimum number of lenses, and focusing is performed by using a single lens.
In [1–3, 5–9] the design of inner focusing lenses is described, in which aspherical lenses are used to achieve high image quality. In the lenses presented in this article, all lenses are spherical [4], which greatly simplifies their production and assembly.
Lenses with 16 mm and 50mm focal length are designed for cameras with a 2 / 3″ format (diagonal 11 mm), a lens with 26 mm focal length that designed for night vision devices with 18 mm optical intensifier, a lens with 100 mm a focal length for 4 / 3″ camera format (diagonal 21.6 mm), and a lens with 200 mm focal length for 1″ camera format (diagonal 16 mm).
All lenses are having at least 0.5 contrast value at 80 Lp / mm resolution, which allows you to get a detailed image of distant objects. The close focusing distance ranges from 2.5 m (for 16 mm and 26 mm lenses) to 25 m (for 100 mm and 200 mm lenses).
Moving the focusing single lens and changing the stop aperture is performed by using motorized drives: an autofocus mechanism and an iris diaphragm control.
Design
Figures 1–6 show the layouts of inner focusing lenses and modulation transfer function (MTF) plots. Fig. 1 shows layout and MTF plot of 16mm focal length lens with an aperture of F / 1.8. This is a retrofocus lens with an aperture stop is located between the 3rd and 4th lens. The field of view angle of the lens is 40 degree, the resolution is 80 lp / mm. The lens is focused at a distance up to 2.5 m by moving the 3rd lens by 0.3 mm. At the same time, the image quality remains quite acceptable.
A compact and lightweight 5‑element lens with 26 mm focal length has an aperture of F / 1.2 and length of 35 mm is shown in Fig. 2. This lens is designed for night vision devices operating with optical intensifier in the wavelength of 0.4–0.9 microns. The field of view of the lens is 40 degrees, resolution is 40 Lp / mm. The lens is focused at a distance up to 2.5 m by moving the 4th lens element by 0.15 mm.
The 5‑element Petzval lens with 50 mm focal length shown in Fig. 3 has an aperture of F / 1.4. The aperture diaphragm is located before the first lens element. The angular field of view of the lens is 12.5 degree, and the range movement of the 4th lens at a distance of 10 m is ~0.2 mm.
A 8‑element retrofocus lens with 100 mm focal length and an aperture of F / 2.8 is shown in Fig. 4. The field of view lens is 12 degree, the movement range of the 4th single lens at a distance of 10 m is ~0.2 mm.
Fig. 5a shows a 8‑element telephoto lens with a 200 mm focal length. Due to the use of a special glass combination, it has total length of 200 mm. The image quality of the lens practically does not change when refocusing from infinity to a distance of 25 m. The movement range of the 4th single lens is ~0.4 mm.
The lens is designed to work in a wide spectral range (visible and infrared). Fig. 5b shows a MTF plot of the lens for the visible spectral range of 0.4–0.7 µm.
Figure 6 shows MTF plots for the near infrared (0.4–0.9 µm) and the mid-infrared (0.4–1.6 µm) spectral ranges. Modification for the infrared range (NIR and SWIR) is performed by moving the last lens and applying the appropriate anti-reflection coating on the lenses.
To compare inner focusing lenses Fig. 7 shows a layout of 30x zoom lens. The lens consists of 4th groups, where the 1st and 3rd groups does not move. Three aspherical lenses are used to correct aberrations in the lens design. The focal length in the lens is changed by moving the 2nd and 4th groups of lenses, and focusing is done by moving the negative lens in the fixed group 3. The short-range focusing distance is ~200 focal lengths (2–60 m).
Fig. 8 shows MTF plots of zoom lens for two positions. The resolution of the lens at the f′ = 10 mm position is relatively high (contrast >0.5), at the f′ = 300 mm position the resolution drops significantly (contrast <0.3), which is lower than in a fixed-focal length lens. The main parameters of inner focusing lenses are shown in Table.
Conclusion
Lenses with inner focusing are relatively simple designed, have a high image quality and can be a good replacement for more complex and expensive zoom lens which are used in optical devices for varies applications.
AUTHORS
Shishkin Igor Petrovich, Cand. of Tech. Sciences; e-mail: shipoflens@mail.ru; RTC «LEMT» BelOMO, Minsk, Republic of Belarus.
ORCID ID: 0000-0002-4592-1060
Shkadarevich Alexey Petrovich, Dr. of Tech.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
NTC “LEMT” BeloMO, Minsk, Republic of Belarus
The article describes the design of inner focusing lenses. Lenses can be used in surveillance devices, night vision devices, for application in machine vision systems, in photography and other fields. Wide-angle lens with a focal length of 16 mm and an aperture of F / 1.8, fast lens with a focal length of 26 mm and an aperture of F / 1.2, lens with a focal length of 50 mm and an aperture of F / 1.4, lens with a focal length of 100 mm and an aperture of F / 2.8, telephoto lens with a focal length of 200 mm and an aperture of F / 4, as well as for comparison a lens with a variable focal length of 10–300 mm and an aperture of F / 1.6–4.5.
Keywords: inner focusing lens, television lens, surveillance devices, night vision devices, machine vision, photography
Article received: 01.04.2025
Article accepted: 21.04.2025
Introduction
Television lenses with variable focal length are actively used in modern surveillance devices. The range of focal lengths can vary widely (10–60 times) depending on device applications. The use of zoom lenses in observation devices is associated with the perform of two functions: viewing the observed space when using a wide field of view and maximizing the approach of the object when using a narrow field of view.
Since zoom lenses tend to have acceptable image quality over the entire range of focal lengths, it is not possible to obtain the maximum resolution of an object in a narrow field. An alternative solution for obtaining maximum image quality (close to theoretical limit) is fixed-focus lenses.
A distinctive feature of the presented lenses, which have acceptable image quality, is the simplicity of the design – the minimum number of lenses, and focusing is performed by using a single lens.
In [1–3, 5–9] the design of inner focusing lenses is described, in which aspherical lenses are used to achieve high image quality. In the lenses presented in this article, all lenses are spherical [4], which greatly simplifies their production and assembly.
Lenses with 16 mm and 50mm focal length are designed for cameras with a 2 / 3″ format (diagonal 11 mm), a lens with 26 mm focal length that designed for night vision devices with 18 mm optical intensifier, a lens with 100 mm a focal length for 4 / 3″ camera format (diagonal 21.6 mm), and a lens with 200 mm focal length for 1″ camera format (diagonal 16 mm).
All lenses are having at least 0.5 contrast value at 80 Lp / mm resolution, which allows you to get a detailed image of distant objects. The close focusing distance ranges from 2.5 m (for 16 mm and 26 mm lenses) to 25 m (for 100 mm and 200 mm lenses).
Moving the focusing single lens and changing the stop aperture is performed by using motorized drives: an autofocus mechanism and an iris diaphragm control.
Design
Figures 1–6 show the layouts of inner focusing lenses and modulation transfer function (MTF) plots. Fig. 1 shows layout and MTF plot of 16mm focal length lens with an aperture of F / 1.8. This is a retrofocus lens with an aperture stop is located between the 3rd and 4th lens. The field of view angle of the lens is 40 degree, the resolution is 80 lp / mm. The lens is focused at a distance up to 2.5 m by moving the 3rd lens by 0.3 mm. At the same time, the image quality remains quite acceptable.
A compact and lightweight 5‑element lens with 26 mm focal length has an aperture of F / 1.2 and length of 35 mm is shown in Fig. 2. This lens is designed for night vision devices operating with optical intensifier in the wavelength of 0.4–0.9 microns. The field of view of the lens is 40 degrees, resolution is 40 Lp / mm. The lens is focused at a distance up to 2.5 m by moving the 4th lens element by 0.15 mm.
The 5‑element Petzval lens with 50 mm focal length shown in Fig. 3 has an aperture of F / 1.4. The aperture diaphragm is located before the first lens element. The angular field of view of the lens is 12.5 degree, and the range movement of the 4th lens at a distance of 10 m is ~0.2 mm.
A 8‑element retrofocus lens with 100 mm focal length and an aperture of F / 2.8 is shown in Fig. 4. The field of view lens is 12 degree, the movement range of the 4th single lens at a distance of 10 m is ~0.2 mm.
Fig. 5a shows a 8‑element telephoto lens with a 200 mm focal length. Due to the use of a special glass combination, it has total length of 200 mm. The image quality of the lens practically does not change when refocusing from infinity to a distance of 25 m. The movement range of the 4th single lens is ~0.4 mm.
The lens is designed to work in a wide spectral range (visible and infrared). Fig. 5b shows a MTF plot of the lens for the visible spectral range of 0.4–0.7 µm.
Figure 6 shows MTF plots for the near infrared (0.4–0.9 µm) and the mid-infrared (0.4–1.6 µm) spectral ranges. Modification for the infrared range (NIR and SWIR) is performed by moving the last lens and applying the appropriate anti-reflection coating on the lenses.
To compare inner focusing lenses Fig. 7 shows a layout of 30x zoom lens. The lens consists of 4th groups, where the 1st and 3rd groups does not move. Three aspherical lenses are used to correct aberrations in the lens design. The focal length in the lens is changed by moving the 2nd and 4th groups of lenses, and focusing is done by moving the negative lens in the fixed group 3. The short-range focusing distance is ~200 focal lengths (2–60 m).
Fig. 8 shows MTF plots of zoom lens for two positions. The resolution of the lens at the f′ = 10 mm position is relatively high (contrast >0.5), at the f′ = 300 mm position the resolution drops significantly (contrast <0.3), which is lower than in a fixed-focal length lens. The main parameters of inner focusing lenses are shown in Table.
Conclusion
Lenses with inner focusing are relatively simple designed, have a high image quality and can be a good replacement for more complex and expensive zoom lens which are used in optical devices for varies applications.
AUTHORS
Shishkin Igor Petrovich, Cand. of Tech. Sciences; e-mail: shipoflens@mail.ru; RTC «LEMT» BelOMO, Minsk, Republic of Belarus.
ORCID ID: 0000-0002-4592-1060
Shkadarevich Alexey Petrovich, Dr. of Tech.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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