Definition of terms used in Lens Grapher and Previzion

  • Baking
    • The process of adding the row or column offsets into the main data. This is necessary before closing a file because Previzion does not recognize offsets and saving a file in LensGrapher does not automatically bake the offsets into the lens data
  • Column Offset
    • A value added to a complete focus distance set of data
    • When viewing “entry pupil,” adding 12 to the column offset for the nearest focus distance will add 12 units, to “entry pupil” for all focal length steps in just that column
  • Distortion
    • the dependent lens parameter that defines how much radial distortion the Previzion camera will render
  • “Deleted” Point
    • A lens point manually deleted by the user. A deleted point can be undeleted by assigning a new value or undo-ing the deletion. Once saved and the file is closed, the point will be permanently deleted from the file; this point will then load into Lens Grapher as a “missing” point.
  • Dependent Variable
    • This is the collection of lens parameters that the lens calibration process attempts to construct. These dependent variables are so called because they are the product of the zoom and focus of the lens. In other words, these dependent variables are changed when the zoom and or focus of the physical lens changes; the opposite is not true. These dependent variables are: distortion, focal length, entry pupil and viewable area
  • Focal Length
    • This is confusing because focal length can be understood as both a dependent and independent parameter
    • As an Independent Parameter: this marks the zoom of the physical lens and is recorded by the focal length fraction.
    • As a Dependent Parameter: this is the specific, measured focal length of the lens. This value is used in Previzion rendering and post rendering as the focal length of the CG or virtual camera
  • Focal Length Step
    • The unique zoom steps defined when setting up a lens calibration. Previzion samples the physical lens zooming into the number of Focal Length Steps as defined in Previzion.
    • More information can be found by clicking here. Look for the first bullet point.
  • Focus
    • Relates to the focus on the physical lens. Previzion tracks the focus by way of encoders and encodes the focusing into discrete focus steps as defined by the various focus distances
  • Focus Distance Step
    • The number of distances, that Previzion is from the calibration board, as defined in the initial calibration setup process. Find out more by clicking here.
  • Independent Variable
    • This relates to the two physical lens characteristics that define the two controllers: zoom and focus. This creates a 2D matrix of point data: zoom steps multiplied by
  • Lens Parameter
    • a characteristic of the lens recorded for each point in the 2D matrix of independent variables.
  • “Missing” Point
    • Any point defined as not present while opening a lens calibration file. These points cannot be edited in the Lens Grapher and can only be edited in Previzion or by hand in the text file.
  • Offsets
    • any value typed into the row or column offset. These values augment the graph to show what the parameters would look like once baked into the source data. There are unique offsets for entry pupil, distortion and focal length.
  • Rack Focus
    • Changing focus controller on the lens from one end of the focus to the other. As an example, changing the focus from completely near to completely far.
  • Rack Zoom
    • Changing zoom controller on the lens from one end of the zoom to the other. As an example, changing the focus from completely wide/long to completely tight/short.
  • Row Offsets
    • A value added to a complete focal length set of data.
    • When viewing “distortion,” adding 0.32 to the row offset for the tightest focal length step will add 0.32 units, to “distortion” for all focus distances in just that row.
  • Viewable Area
    • This is the combined effect of the two dependent lens parameters: entry pupil and focal length. In detail, this value describes the horizontal area that the virtual lens sees at the specific location of x focal length step and y focus distance.
    • Knowing the horizontal area viewed means you can more quickly see if there is, or will be, slipping in the Previzion render when rack zooming.
  • Zoom
    • Relates to the zoom of the physical lens. Previzion tracks the zoom by way of encoders and encodes the zooming into discrete focus steps as defined by the various focus distances. The standard amount of zoom steps is 21.

Last Modified: August 1, 2014