How choose camera?

1. Resolution: High vs. Low

  • High-resolution cameras (e.g., 8K, 12MP, 20MP):
    • When to choose:
      • When you need to inspect very small details or cover a large area with high accuracy.
      • For applications like PCB inspection, fine defect detection, or multi-part analysis in one image.
    • Considerations:
      • Higher price, larger image files, more processing power required.
      • May require higher-quality lenses/objectives.
  • Low-resolution cameras (e.g., VGA, 1MP, 2MP):
    • When to choose:
      • For simple presence/absence checks, large object detection, or when high detail is not required.
      • When cost, speed, or network bandwidth are more important than fine detail.
    • Considerations:
      • Lower price, faster processing, smaller data size.
      • Suitable for basic sorting, counting, or position detection.

2. Choosing the Objective (Lens)

  • Focal length:
    • Determines the field of view (FOV) and working distance.
    • Short focal length (e.g., 8mm, 12mm):
      • Wide FOV, suitable for close-up or large area coverage.
    • Long focal length (e.g., 25mm, 50mm):
      • Narrow FOV, suitable for distant or detailed inspection.
  • Aperture (f-number):
    • Lower f-number = more light, shallower depth of field.
    • Higher f-number = less light, greater depth of field.

Resolution compatibility:

Use high-quality (megapixel-rated) lenses for high-resolution cameras to avoid image blur or distortion.

3. When is Camera Speed Important?

  • High-speed cameras (high frame rate):
    • Needed when inspecting fast-moving objects (conveyor belts, robotic arms).
    • Important for real-time or inline inspection, tracking, or counting.
    • Example: 100+ fps for high-speed pick-and-place, 30+ fps for general automation.
  • Low-speed cameras:
    • Suitable for static or slow-moving objects.
    • Example: Manual inspection stations, slow conveyors.

4. Calculating Focal Length and Pixel Size

A. Field of View (FOV) Calculation

  • FOV = (Sensor size × Working distance) / Focal length
    • Sensor size: Width or height of the camera sensor (in mm)
    • Working distance: Distance from lens to object (in mm)
    • Focal length: Lens focal length (in mm)

B. Pixel Size and Resolution

  • Object size per pixel = FOV / Number of pixels (sensor width or height)
    • Example: If FOV is 100mm and camera resolution is 4000 pixels wide:
      • 100mm / 4000 pixels = 0.025mm (25μm) per pixel
  • To resolve a feature of X mm, you need at least 2 pixels per feature (Nyquist):
    • Required pixel size = Feature size / 2

C. Choosing the Right Combination

  • For fine detail:
    • Use high-resolution camera + appropriate lens for small FOV and small pixel size.
  • For large objects:
    • Use lower resolution or wide-angle lens for larger FOV, larger pixel size.

5. Summary Checklist

  • Define the smallest feature you need to detect.
  • Calculate the required FOV and working distance.
  • Choose a camera resolution that gives at least 2 pixels per feature.
  • Select a lens with the correct focal length for your FOV and working distance.
  • Ensure lens quality matches camera resolution.
  • Consider frame rate for moving objects.

Camera examples

1) 2MP 1080P USB Camera 

Camera Parameters

  • Sensor size: 1/2.8" (approx. 5.6mm × 3.1mm, width × height)
  • Resolution: 1920 × 1080 pixels
  • Focal length: Example: 16mm (adjust if you want a different value)
  • Working distances examples: 100mm, 250mm, 400mm

1. Field of View (FOV) Calculation

Formula:
FOV (width) = (Sensor width × Working distance) / Focal length
FOV (height) = (Sensor height × Working distance) / Focal length

A) Working distance: 100mm (10 cm)

  • FOV width = (5.6mm × 100mm) / 16mm = 35mm
  • FOV height = (3.1mm × 100mm) / 16mm = 19.4mm

B) Working distance: 250mm (25 cm)

  • FOV width = (5.6mm × 250mm) / 16mm = 87.5mm
  • FOV height = (3.1mm × 250mm) / 16mm = 48.4mm

C) Working distance: 400mm (40 cm)

  • FOV width = (5.6mm × 400mm) / 16mm = 140mm
  • FOV height = (3.1mm × 400mm) / 16mm = 77.5mm

2. Pixel Size in Object Space

Formula:
Pixel size (object) = FOV width / number of pixels (width)

A) 100mm distance

  • Pixel size = 35mm / 1920 = 0.0182mm (18.2μm)

B) 250mm distance

  • Pixel size = 87.5mm / 1920 = 0.0456mm (45.6μm)

C) 400mm distance

  • Pixel size = 140mm / 1920 = 0.0729mm (72.9μm)

3. Position Accuracy (Theoretical)

Rule of thumb:

  • Theoretical best accuracy ≈ 1 pixel (if subpixel interpolation, can be 0.1–0.2 pixel in ideal conditions)
  • Practical accuracy: 2–5× pixel size (depends on optics, lighting, calibration, etc.)

A) 100mm distance

  • Best-case accuracy: 0.018mm (18μm)
  • Practical: 0.04–0.09mm (40–90μm)

B) 250mm distance

  • Best-case accuracy: 0.046mm (46μm)
  • Practical: 0.09–0.23mm (90–230μm)

C) 400mm distance

  • Best-case accuracy: 0.073mm (73μm)
  • Practical: 0.15–0.36mm (150–360μm)


2) 5MP Mini USB Camera 

Camera Parameters

  • Model: ELP 5MP Mini USB Camera
  • Sensor: 1/2.5" Aptina MI5100 (sensor size approx. 5.7mm × 4.28mm)
  • Resolution: 2592 × 1944 pixels
  • Lens: M12, 3mm focal length, HFOV ≈ 85–90°
  • Working distances: 20mm, 100mm, 200mm

For calculations, we'll use the sensor width (5.7mm) and the specified focal length (3mm).

1. Field of View (FOV) Calculation

Formula:
FOV (width) = (Sensor width × Working distance) / Focal length
FOV (height) = (Sensor height × Working distance) / Focal length

A) Working distance: 20mm

  • FOV width = (5.7mm × 20mm) / 3mm = 38.0mm
  • FOV height = (4.28mm × 20mm) / 3mm = 28.5mm

B) Working distance: 100mm

  • FOV width = (5.7mm × 100mm) / 3mm = 190.0mm
  • FOV height = (4.28mm × 100mm) / 3mm = 142.7mm

C) Working distance: 200mm

  • FOV width = (5.7mm × 200mm) / 3mm = 380.0mm
  • FOV height = (4.28mm × 200mm) / 3mm = 285.3mm

2. Pixel Size in Object Space

Formula:
Pixel size (object) = FOV width / number of pixels (width)

A) 20mm distance

  • Pixel size = 38.0mm / 2592 = 0.0147mm (14.7μm)

B) 100mm distance

  • Pixel size = 190.0mm / 2592 = 0.0733mm (73.3μm)

C) 200mm distance

  • Pixel size = 380.0mm / 2592 = 0.1466mm (146.6μm)

3. Position Accuracy (Theoretical)

Best-case (1 pixel):
Practical (2–5 pixels):

A) 20mm distance

  • Best-case: 0.015mm (15μm)
  • Practical: 0.03–0.07mm (30–70μm)

B) 100mm distance

  • Best-case: 0.073mm (73μm)
  • Practical: 0.15–0.37mm (150–370μm)

C) 200mm distance

  • Best-case: 0.147mm (147μm)
  • Practical: 0.29–0.73mm (290–730μm)

3) 48MP camera, 5-50mm Lens, support 10X optical zoom

1. Field of View (FOV) Calculation

Formula:
FOV (width) = (Sensor width × Working distance) / Focal length
FOV (height) = (Sensor height × Working distance) / Focal length

A) Working distance: 100mm

  • FOV width = (6.4mm × 100mm) / 16mm = 40.0mm
  • FOV height = (4.8mm × 100mm) / 16mm = 30.0mm

B) Working distance: 300mm

  • FOV width = (6.4mm × 300mm) / 16mm = 120.0mm
  • FOV height = (4.8mm × 300mm) / 16mm = 90.0mm

C) Working distance: 500mm

  • FOV width = (6.4mm × 500mm) / 16mm = 200.0mm
  • FOV height = (4.8mm × 500mm) / 16mm = 150.0mm

2. Pixel Size in Object Space

Formula:
Pixel size (object) = FOV width / number of pixels (width)

A) 100mm distance

  • Pixel size = 40.0mm / 8000 = 0.005mm (5μm)

B) 300mm distance

  • Pixel size = 120.0mm / 8000 = 0.015mm (15μm)

C) 500mm distance

  • Pixel size = 200.0mm / 8000 = 0.025mm (25μm)

3. Position Accuracy (Theoretical)

Best-case (1 pixel):
Practical (2–5 pixels):

A) 100mm distance

  • Best-case: 0.005mm (5μm)
  • Practical: 0.01–0.025mm (10–25μm)

B) 300mm distance

  • Best-case: 0.015mm (15μm)
  • Practical: 0.03–0.075mm (30–75μm)

C) 500mm distance

  • Best-case: 0.025mm (25μm)
  • Practical: 0.05–0.125mm (50–125μm)

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