Distance between the object side principal point and the object.
For larger distances, this is about the working distance
The symmetry axis of a lens or a lens system.
Optical density is a measure used for filters to describe how much light of a blocked wavelength still passes the filter
the optical density is given by the formula:
ODn = 10^-n = 1/10^n
OD0 = 10^-0 = 1/10^0 = 1 = 100% light
OD1 = 10^-1 = 1/10^1 = 0.1 = 10% light
OD2 = 10^-2 = 1/10^2 = 0.01 = 1% light
OD3 = 10^-3 = 1/10^3 = 0.001 = 0.1% light
OD4 = 10^-4 = 1/10^4 = 0.0001 = 0.01% light
The optical density is an input value, demanded by the Application.
OD2 equals 1 percent.
For a camera of 256 intensity levels this equals 2.6 intesity values. This is not much stronger than the sensor noise.
OD3 entspricht 0.1 Prozent.
For a camera of 256 intensity levels this equals 0.26 intesity values. This is less than the sensor noise.
The higher the number the better the blocking.
The higher the number the more expensive the filter.
Typical values for comemrcial filters are OD2,
higher quality filters have OD3
Filters ilters for outdoor use might need OD4 or higher to block too intensive sunlight.
For a + b = c we get ODa + ODb = ODc
so you can generater an OD6 filter by two OD3 filters. However, the optics should be prepared for the thicker glass then.
May the width of an object be 1.6mm and the sensor width = 4.8mm
May the width of an object be 36mm and the sensor width = 3.6mm
The optical path length is proportional to the time light needs to travel between two points
In a homogenous medium with refractuion index n and physical point distance d this formula simplifies to
In glass with the index of refraction
of 1.5 for some wavelength for a physical point distance of d=10mm the optical path length
As glass has a different index of refraction
for different wavelengths, the OPL
is different for each wavelength
Some OPLs for glass type BK7 and a physical point distance of d=10mm
[table caption=”sample OPLs for BK7″ width=”400″ colwidth=”100|100|100|100″ colalign=”left|left|left”]
wavelength,index of refraction
,phys. distance, OPL
In paraxial imaging system all of the light
rays connecting a source point a to it’s image point have equal OLPs
F# with the largest possible DOF.
Larger F# reduces the DOF due to diffraction
orthographic lenses are a type of fisheye lenses
orthographic lenses are also called” hemispherical“or “orthographisch”
lenses use an image mapping function of type
maintains planar illuminance
[table caption=”orthographic angles” width=”500″ colwidth=”50|50|50|50″ colalign=”center|center|center|center”]
An orthographic / hemispherical fisheye, uses a parallel projection of a hemisphere onto a plane. The resulting image will obviously be circular. The widest view angle is 180 degrees. At +/-90 degrees extreme distortion will occur. Due to this heavy distortion it’s less often used than f-Theta / angular fisheye.