Lens calibration is a crucial process in vfx compositing and proper camera tracking. This allows Previzion to correctly map and calculate the lens focal length, distortion and entry pupil.
This process is done on a per Serial Number basis as each lens may significantly vary from the next.

Depending on the number of lenses and your level of experience, this process can take longer.

  • Time: 3Hrs per lens
  • People Recommend: 2 people
  • Skill Type: Camera/li>

Hardware Required:

  • HD Camera
  • Tripod or Camera Support
  • Lense(s) to be Calibrated
  • Lens Controller
  • Corresponding batteries and accessories
  • Additional Work Light
  • Proper Camera Mounts and Rails
  • Metric Measuring Tape
  • Lens Calibration Motor and Stand
  • Lens Calibration Board(s)
  • Foot Switch
  • Power Extension Cord (Stinger)
  • Airtrack
  • Lens-Controller-to-Airtrack Cable
  • Video Breakout Box
  • Previzion Basebox (“DIAL” box)
  • Cable Tether

Software Required:

  • Previzion Application

Setting up Lens Calibration

  1. Verify that room being used is large enough for calibration process
  2. Mount Calibration Motor on Stand
  3. Mount Calibration Board on Motor
  4. Add Calibration Board extension wings (when applicable)
  5. Plug foot switch to motor and power
  6. Verify that Calibration Board clears its oscillating motion
  7. Add a work light to illuminate Calibration Board if necessary
  8. Build Camera with Airtrack
  9. Run cable tether between Previzion and Camera
  10. Connect cable tether to camera and Airtrack
  11. Setup Previzion System and Video Breakout Box
  12. Connect cable tether to Breakout Box

Lens Calibration Process

  1. Power Up Camera
  2. Set Camera to recommended settings
  3. Move Camera as close to target as possible before it hits the board and the lens is still able to focus on the board (this will be your practical minimum focus)
  4. Verify that Calibration Board clears its oscillating motion
  5. Measure practical minimum focus
  6. Startup Previzion Application
  7. Disable all trackers but Sync Source and Lens
  8. Load tracker File
  9. Start “New Calibration”
  10. Set Calibration Steps and Distances
  11. Verify Lens Controller is set to proper orientation
  12. Correct Lens Controller orientation is necessary
  13. Follow On Screen instructions
  14. Save data along the way

Checking Calibration

  1. Load Previzion Default scene with Video Enabled
  2. Enable Screen Text to view Focus Distance/Focal Length
  3. Set Keyer so that CG image can be seen along with live action image
  4. Go through the various focus distances that were calibrated on the lens controller
  5. Slowly zoom from wide to telephoto at each focus distance
  6. Verify that CG matches foreground
  7. Make note of distances that may require tweaking

Correcting Lens Calibration Data

  1. Launch Lightcraft Lens Grapher
  2. Load Calibration File
  3. Save as copy
  4. Locate problematic focus distances
  5. Normalize aberrations and correct faulty points
  6. Save changes
  7. Load corrected lens file in Previzion
  8. Re-Verify Calibration