Why The Lens Grapher is Used

The importance of the .cam file is to accurately register the virtual and real world camera lenses. Occasionally the calibration process may produce bad values for one of the three lens parameters (entry pupil, distortion or focal length. Read more about them in the glossary). If the operator catches them during calibration they may be easily fixed by redoing the calibration step but occasionally the calibration process produces a bad result that needs to be either averaged out with its surrounding values or deleted and replace with a better solution. The best way to see these errors is to graph the points over the zoom or focus range as they will appear as a spikeĀ  or inconsistent value. Hence the graphical usefulness of the Lens Grapher.


Lens Grapher Introduction

The Lens Grapher is Lightcraft’s tool for visualizing and editing lens files (*.cam) created in Previzion. The Lightcraft Lens Grapher Utility is designed to give Previzion operators and lens calibrators the tools necessary to quickly and visually view and edit a Lightcraft Lens Calibration file. The graphing utility gives users the chance to view the important lens parameters through the extents of both rack zooming (defined by number of zoom steps per focus distance) and rack focusing (number of focus distances). Over both zoom and focus axes, the editor displays both table and chart data for these three important parameters (AKA dependent variables):

  • calculated focal length of lens
  • entry pupil of lens
  • distortion value of lens


The program’s icon is very similar to other Lightcraft Icons, with only a slight modification to signify it’s specific function.


Features

  • Reads the following types of lens (*.cam) files:
    • Incomplete Lens Files
    • Zoom Lenses
    • Prime Lenses
    • Zoom Lenses calibrated to a single Focus Distance
  • Missing Data Point signifier
  • Undo / Redo
  • Adding Row and Column Offsets
  • Baking Offset Data
  • Independent Graphs for: Entry Pupil, Distortion and Focal Length Lens Parameters
  • Graph for “Viewable Area” Lens Characteristic
  • Toggle Lens Parameter graphing over choice of Rack Zoom or Rack Focus
  • Data Point Editing in Spreadsheet style Table
  • Analogous Data Highlighting between Graph and Table
  • Hotkeys
  • Averaging Multiple Data Points together
  • Force inclusion of zero as min or max when graphing
  • Show or Hide non-Highlighted graphs with opacity slider and Hotkey
  • Help menu with information about program build, calibration file construction and illustrations of lens parameters
  • Pop-up information when mouse hovering over a point in the graph

The Lens Grapher is an easy to use graphing application that lets Previzion operators view the quality of the lens calibration graphically. Operators can view the lens file whether it’s completed or incomplete, as during the middle of a calibration. The Lens Grapher can be used to view the quality of the calibration for zoom lenses, prime lenses, or calibrations with one focus distance.

Here are examples of lens calibration files that are complete and incomplete:

 

Complete Lens File
Incomplete Lens File: Notice the “missing” vs. “deleted” points
Here are examples of a zoom lens, prime lens, single focus zoom lens file:
The rows represent zoom steps. The columns represent focus distances
Example of a Prime lens with only one (the default) focal length
A Zoom lens with a single focus distance
 

Last Modified: March 6, 2012