Lecture on ND Filters and Their Numbers

Introduction

• Previous video showcased sample photos using ND filter.
• This video addresses questions about ND filter numbers and their meanings.
• Note: If you dislike math, you might find parts of this video boring, but it's beneficial for understanding filter packaging.

Basics of Light Stops

• One stop of light: Amount of light doubled or halved.
• Camera exposure triangle: Shutter speed, ISO, Aperture.
  • Shutter speed: Example from 1/100 to 1/200 (halving light).
  • ISO: Example from 200 to 100 (halving light).
  • Aperture: More complex (refer to a table of f-stops).
    • Sequence: 1, 1.4, 2.8, 4, 5.6 (each represents one stop).

Importance of Understanding ND Filter Numbers

• Helps in deciding how many stops you need when buying an ND filter.
• Multiple Expression Methods:
  1. Stops: 2-5 stop or 6-9 stop.
  2. Decimal: 0.3, 0.6, 0.9
  3. ND Numbers: ND2, ND4, ND8, ND16
     • ND2 = 1 stop (2^1)
     • ND4 = 2 stops (2^2)
     • ND8 = 3 stops (2^3)
     • ND16 = 4 stops (2^4)

Example

• ND2000 filter equals 11 stops (2^11 ≈ 2048).
• Rounded to 2000 by manufacturers.

Practical Application

1. Set your desired exposure (ISO, shutter speed) without a filter.
2. Example: Shutter speed at 1/200, f4, ISO 200, image too bright.
3. Calculation for stops needed:
   • 1/200 to 1/400 = 1 stop
   • 1/400 to 1/800 = 2 stops
   • 1/800 to 1/1600 = 3 stops
   • Metering shows correct exposure at 1/1600.

Quiz Example

• Desired shutter speed change: 0.4s to 30s.
• Calculation:
  • 30 / 0.4 = 75.
  • 2^6 ≈ 64, 2^7 ≈ 128.
  • 75 lies between 6 and 7 stops.

Conclusion

• When unsure, a variable ND filter is useful.
• Reduces the need for exact calculations and frequent filter changes.
• Despite some criticisms (e.g., potential vignettes), it offers practical advantages.
• Creative uses extend beyond just darkening images.

Closing

• Encouragement to view previous ND filter video.
• Reminder to subscribe and like the video.