Some key professional skills in industrial lenses(2)

18. Depth of Field: The depth from the nearest to the farthest point where the sharpest focus is achieved when the CCD moves in and out from the optimal focus point. The depth range on the image side is referred to as the depth of field.

19. Back Focal Length (mm): The distance from the front end of the lens mounting flange to the image plane.

20. C-mount Specifications:

• Name: Standard Outer Diameter
• Thread Count: 32 Threads per inch (TPI) for a diameter of 25.4mm
• Back Focal Length: 17.526mm

21. Numerical Aperture NA, NA':

• NA is the product of the refractive index (n) and the sine of the half-angle (u) created by the object at the entrance pupil.
• NA' is the product of the refractive index (n') and the sine of the half-angle (u') on the image side at the exit pupil.

NA = n × sin(u)     NA' = n' × sin(u')

The higher the NA, the better the resolution and brightness of the lens. Numerical Aperture (NA) on the object side is related to the magnification rate.

For macro lenses:

• NA = (M/2) × F
• NA' = (1/2) × F
• NA = NA' × optical magnification
• NA' = NA × optical magnification

22. F-Number (F No): Indicates the brightness of the lens. It's derived from dividing the lens's focal length by the diameter of the entrance pupil (D mm). The smaller the F-Number, the brighter the lens. Formula: F-No = Focal Length / Entrance Pupil Diameter or Effective Aperture.

23. Effective F-Number: Refers to the actual brightness of the lens at finite distances, indicating the brightness during actual operation. Higher optical magnification results in darker images.

Effective F = (1 + Optical Magnification) × F#    Effective F = Optical Magnification / 2NA

24. Optical Magnification β: The ratio of the object's size to the image size.

β = y' / y    = b / a    = NA / NA'    = CCD Sensor Size / Actual Field of View

25. Optical Zoom Magnification: Refers to the magnification through optical lenses. It indicates the relationship between the focal length and the field of view of the object.

26. Electronic Zoom Magnification: The ratio of the displayed image magnification on a monitor compared to its size on the CCD.

27. Monitor Zoom Magnification: The magnification ratio on a monitor achieved through optical and electronic zoom.

Monitor Zoom Magnification = (Optical Magnification β) × (Electronic Magnification)

28. Field of View (FOV): The visible area on the object side when using a camera.

Vertical Field of View = Camera's Effective Vertical Length / Optical Magnification Horizontal Field of View = Camera's Effective Horizontal Length / Optical Magnification