How to use the Lens Grapher Application

1. Launch Lens Grapher

  • Lens Grapher can be found on your Previzion system
    • It is in the following directory:
      • C:\Program Files\Lightcraft\LensGrapher
    • It is accompanied by 3 .dll files. These files are Mandatory and MUST be in the same directory as the main program file
      • QtCore4.dll
      • QtGui4.dll
      • QtXml4.dll
  • If you don’t have a Previzion machine, or _Lens Grapher_ isn’t installed on your system, you can download it from here:
  • You can also run this on any Win7 x64 system with the latest updates

2. Open a file

You can open a file one of there separate ways:

  • Hotkey
    • CTRL+O
  • Button
  • Menu

3. Make sure the same lens file is loaded into Previzion

Instructions on how to load a lens file into Previzion can be here: http://lightcrafttech.com/support/documentation/lens-interface/lens-calibration-panel/

4. Use Previzion to look for errors in rendering

Now that the lens file is loaded, step through all focus and zoom steps with your lens controller. Make sure to step through the full range of focus for each zoom step, and vice versa. Look for pops in zoom (as in, when the video is zooming in but the CG elements do not zoom in at all, or at the same rate); these are errors in either focal length or entry pupil. Also look for pops in when stepping through your focus controller (when the CG elements do not bow or bend the same way as the live video); this indicates an error in the distortion values for the lens.

  • Write down the focus distance fraction and the focal length fraction from Previzion when you see an error.

These fractions will help you pinpoint where to locate your errors in the Lens Grapher application. If you can’t find these two fractions, then Enable Screen Text and view the Focal Length and Focus Distance values.


5. When an error is found, Use Lens Grapher to fix the data

When searching for errors in a lens file, there are two properties that need to be checked and corrected: distortion and viewable area.

  • Distortion
  • Viewable Area


The distortion parameter defined how much radial distortion the virtual lens renders. Remember, the virtual lens and physical lens characteristics are supposed to match. So if the physical lens is adding barrel distortion to the video feed, but the virtual lens is adding pincushion distortion to the CG rendering, then an error exists in the lens calibration file.

An error in the file may also exist if the virtual lens does not distort the CG elements to the same degree as the video feed from the physical lens, even if both are rendering barrel – or pincushion – distortion.

Viewable Area

Viewable Area is the combination of two lens parameters: focal length and entry pupil. If you notice any sliding between the CG and live video elements, in Previzion, chances are there’s an error in either an entry pupil or focal length value.

NOTE: Please adjust entry pupil and focal length when looking at the “Viewable Area” graph (CTRL + F). What you see below is an example of a lens file, while viewing it’s “viewable area.” Notice that at Focal Length 10 there is a spike in entry pupil which is causing the drop in viewable area.

Because viewable area isn’t a parameter in the lens file, entry pupil must be changed in order to fix the rendering problems that will arise if this is left uncorrected.

How to Correct

Make all adjustments to data in the chart on the right by typing in corrected values.

If you need to average multiple cells together, select all cells that will be used to generate the average value, then select the cell that will receive the average and Average the Selected Cells (SHIFT + A).

6. Save the file and reload in Previzion

  • Use the hotkey for saving (CTRL + S) to save this to a new file.
  • Reload the file into Previzion

7. Check the results

  • Check the results of your lens fixes in Previzion by walking through the complete zoom range, and the complete focus range at each zoom step.

8. Repeat Steps 4 – 7 as necessary