Ghost Image Analysis
Ghost image analysis is based on the built-in
inverse ray trace algorithm, which does not require to rebuild the optical system,
that is inserting and duplicating surfaces which represent the ghost path.
This allows instantaneous ghost analysis and a very fast way to identifying
the most disturbing surface combinations.
|Conventional Ray Trace
||Ghost Ray Trace
Ghost Images are due to the fact that optical systems can form unintended images due to reflections between pairs of surfaces.
All lens surfaces reflect light to an extent depending on the refractive index of the
glass itself respectively on the type of anti-reflection coating applied to these surfaces.
Light reflected from the inner surfaces of a lens will be reflected again and may form
reasonably well-defined images close to the image surface. Such spurious images are called
The number of possible surface combinations (pairs) which may contribute to ghost images
, where n
is the number of lens surfaces in the system. As the number of surfaces
grows, the probability of ghost problems also increases. For example, a zoom lens with 10 lenses
(20 surfaces) gives 190 possible ghost images.
Photorealistic Rendering of Ghosts:
OptaliX provides the most realistic and accurate ghost analysis. It offers a fully automatic search
of ghost effects by evaluating ALL possible surface pairs in a lens which may contribute to ghosts.
That includes wavelength dependent effects of multilayer coatings on optical surfaces, material absorption
The image below is the rendered ghost image on a 10-lens element objective including AR-coatings and
absorption in lenses.
||Unlike in other optical design programs, OpTaliX does not require a preselection of the most
disturbing ghost surface pairs on a paraxial basis (which can be extremely misleading, if not
totally wrong), nor does it require to rebuild a design for each individual ghost surface pair, writing macros,
storing massive ray data to files and/or display the data with the help of external programs,
as required in other software packages.
OptaliX entirely avoids such tedius and inefficient work! Note that the image to the left was rendered
from the scratch in about 20 minutes on a 1.7GHz Pentium machine, including all (184) surface
combinations, AR-coatings and absorption effects, whereas in other programs
you will need hours or days for creating and testing macros and program interfaces.
Ghost Raytrace in GRIN Elements:
This example shows the ghost raytrace in a radial GRIN element (SelfocTM
rod) where the
first reflection takes place on surface 3 and the second reflection takes place on
surface 2. The surface numbers indicate that additional dummy surfaces are NOT required to simulate
the ghost path. This way, ghost analysis is instantaneous.