About Cinematography

Selection of camera lenses

1. Introduction

There are many types of camera lenses: classified in terms of focal length, they can be divided into short focal length, medium focal length and long focal length. and zoom lenses; from the size of the field of view, they can be divided into wide-angle, standard, narrow or telephoto lenses; from the structure, they can be divided into fixed aperture fixed focus, manual aperture fixed focus, automatic aperture fixed focus, manual zoom , automatic aperture, electric zoom, electric three-variable, pinhole and other lens types. In TV surveillance systems, except for single-board computers or ultra-small all-in-one computers, the cameras generally referred to refer to CCD bare metal. Therefore, whether the lens selection is appropriate or not is directly related to the quality of the camera. Therefore, in the design of a TV monitoring system, lens selection is one of the most critical and important aspects. The following is an introduction to several specific issues in lens selection.

2. Lens Selection Ruler and Cheat Sheet

After years of development, there are now many practical tables and tools to greatly simplify the workload of lens selection.

(1) Lens Selection Cheat Sheet

Tables 1, 2 and 3 are American Herman lenses. A cheat sheet recommended by Kruger in The Complete CCTV Handbook, which lists the scene sizes that 1/2, 2/3 and 1/3-inch sensors can see at specific object distances and focal lengths, and vice versa. Choose the focal length of the lens based on object distance, scene size, etc. The feet and inches in the table only need to be converted to the metric system (1 foot = 30.48 centimeters; 1 inch = 2.54 centimeters). To calculate the scene dimensions (width and height) that a 1-inch sensor can see, simply multiply all scene dimensions in the 1/2-inch sensor data table (Table 1) by 2. For 1/3-inch sensors, you can look it up in Table 2, or you can divide the scene size by 2 in the data table for 2/3-inch sensors (Table 2).

A proper understanding of Tables 1, 2, and 3 will make the job of selecting a lens for a specific field of view easier. For example, we want to use a 1/2-inch camera to observe the entire scene with a width of 20 feet and a height of 15 feet from a distance of 40 feet. Look up Table 1 and find 20.6×15.5 from the distance 40 down to achieve the required scene. Its corresponding focal length is 12, so it is just right to choose a lens with a focal length of 12 mm.

If you use a 2/3-inch camera according to the same distance and scene requirements, and look up Table 2 in the same way, you can choose to capture a scene with a width of 22.5 feet and a height of 16.7 feet. A lens with a focal length of 16 mm;

If you use a 1/3-inch camera according to the same distance and scene requirements, you can also choose a shooting width of 22.0 feet by looking up Table 3 in the same way and a 16.4-foot-tall scene with a focal length of 8 mm.

Table 1: Relationship between scene size, lens focal length and scene object distance (1/2-inch camera)

1/2-inch sensor lens selection table

< p> Focal length mm Distance D between camera and scene (in feet)

Field of view: width H and height V (in feet)

5 10 20 30 40 50 75

H×V H×V H×V H×V H×V H×V H×V

2.6

3.5

4.0

4.8

6.0

7.5

8.0

12.0

16.0

p>

25.0

50.0

75.0

150

12.1×9.3

9.0×6.9

7.8×6.0

6.5×4.8

5.1×3.9

4.1×3.1

3.9×3.0

2.6×1.9

1.9×1.5

1.3×1.0

.62×.46

. 41×.31

.21×.16 24.9×18.8

18.5×14.0

15.6×11.6

12.9×9.7< /p>

10.3×7.8

8.3×6.2

7.8×5.8

5.2×3.9

3.9×2.9< /p>

2.3×2.0

1.2×.93

.82×.62

.41×.31 48.5×37.7

36.0×28.0

31.0×23.2

25.9×119.5

20.7×15.5

16.5×12.4

15.5×11.6

10.3×7.8

7.8×5.9

5.2×3.0

2.5×1.9

1.7×1.2

.85×.60

72.6×55.8

54.0×41.4

46.8×36.0< /p>

39.0×28.8

30.6×23.4

24.6×18.6

23.4×18.0

15.6×11.4< /p>

11.4×9.0

7.8×6.0

3.7×2.8

2.5×1.9

1.3×1.0 98.3 ×74.0

73.0×55.0

62.0×46.4

51.7×38.8

41.3×31.0

33.0 ×24.8

31.0×23.2

20.6×15.5

15.5×11.6

10.0×7.8

4.9 ×3.7

3.3×2.5

1.7×1.3

123.8×94.2

92.0×70.0

77.6 ×58.2

64.6×48.8

51.6×38.8

41.3×31.0

38.8×29.1

25.8 ×19.4

19.4×14.5

13.0×9.7

6.2×4.7

4.1×3.1

2.1 ×1.6

185.8×141.0

138.0×105.0

116.4×87.4

96.9×72.6

77.4 ×58.2

62.0×46.5

58.2×43.7

38.7×29.1

29.1×21.8

19.5 ×10.1

9.3×7.1

6.2×4.7

3.1×1.9

Note: 1/2-inch lens cannot be used with 2/ For use with 3 or 1 inch sensors (the lens is too small).

Table 2: Relationship between scene size, lens focal length and scene object distance (2/3-inch camera)

2/3-inch sensor lens selection table

< p> Focal length mm Distance D between camera and scene (in feet)

Field of view: width H and height V (in feet)

5 10 20 30 40 50 75

H×V H×V H×V H×V H×V H×V H×V

4.0

4.8

6.5

8.0

12.5

16.0

25.0

50.0

75.0

p>

100

150

11.0×8.2

10.0×7.5

6.8×5.0

5.5×4.1

3.5×2.6

2.8×2.1

1.7×1.3

.84×.63

.58×.43

.42×.32

.29×.22

22.0×16.4

20.0 ×15.0

13.6×10.1

11.0×8.2

7.0×5.3

5.6×4.2

3.6 ×2.7

1.7×1.3

1.1×.98

.85×.65

.55×.49

44.0×33.0

40.0×30.0

27.0×20.3

22.0×16.5

14.0×10.5

11.1×8.3

7.0×5.3

3.3×2.4

2.2×1.6

1.7×1.2

1.1×.80

66.0×49.2

60.0×45.0

40.8×30.3

33.0×24.6

21.0×15.6

16.8×12.6

10.5×8.0

5.0×3.8

3.5×2.6

2.5×1.9

1.8×1.3

88.0×64.0

80.0×60.0

54.2×39.4

44.0×32.0

28.0×21.0

22.5×16.7

14.0×10.7

6.5×4.9

4.3×3.2

3.3×2.5

2.2×1.6

112.0×84.0

100.0×75.0

68.9×51.7

56.0×42.0

35.0×26.2

28.0×21.0

22.5×16.7

14.0×10.7

6.5×4.9

4.2×3.2

2.8×2.1

168×126

150×125

103.4×77.6

84.0×63.0

52.0×39.3

42.0×31.5

27.0×20.0

12.5×9.4

8.3×6.2

6.3×4.2

4.2×3.1

p>

Note: 2/3-inch lens cannot be used with 1-inch sensor (lens is too small)

Table 3: Relationship between scene size, lens focal length and scene object distance (1 /3-inch camera)

1/3-inch sensor lens selection table

Focal length mm Distance D between camera and scene (in feet)

Field of view: Width H and Height V (in feet)

5 10 20 30 40 50 75

H×V H×V H×V H×V H×V H×V H× V

2.8

3.3

3.8

4.0

4.5

6.7< /p>

8.0

9.0

7.9×5.6

6.7×5.0

5.8×4.3

< p> 5.5×4.1

5.0×3.8

3.3×2.5

2.8×2.1

2.5×1.9

< p> 15.8×11.2

13.4×10.0

11.6×8.6

11.0×8.2

10.0×7.6

< p> 6.6×5.0

5.5×4.1

5.0×3.8

31.6×22.4

26.8×20.0

< p> 23.2×17.2

22.0×16.4

20.0×15.2

13.2×10.0

11.0×8.2

< p> 10.0×7.6

47.4×33.6

40.2×30.0

34.8×25.8

33.0×24.6

< p> 30.0×22.8

19.8×15.0

16.5×13.7

15.0×11.4

63.2×44.8

< p> 53.6×40.0

46.4×14.4

44.0×33.0

40.0×30.4

26.4×20.0

< p> 22.0×16.4

20.0×15.2

79.0×56.0

67.0×50.0

58.0×43.0

< p> 55.0×41

50.0×38

33.0×25

27.5×20.5

25.0×19.0

< p>118.5×84.0

100.5×75.0

87.0×64.5

82.5×61.5

75.0×57.0

< p> 49.5×37.5

41.0×30.8.

37.5×28.5

Note: 1/3-inch lens cannot be used with 1/2, 2/3 and For use with a 1-inch sensor (the lens is too small)

(2) Lens selection ruler

From the relevant formulas of the previous lens, it can be seen that due to the imaging size, focal length, and field of view of the lens Parameters such as angle have a one-to-one correspondence. Therefore, some professional lens manufacturers (such as Computar and Seiko, etc.) have also specially produced lens selection slide rules as shown in Figure 1. The slide rule consists of two upper and lower discs and a transparent sector piece. There are scales on the disc and sector sheet, which are respectively marked with the field of view, the horizontal and vertical dimensions of the object, the focal length of the lens, and the photosensitive surface of the CCD chip. Parameters such as size and distance of the subject from the CCD camera.