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Ob Op Or

Object distance

Distance between the object side principal point and the object.
For larger distances, this is about the working distance

Optical Path Length

The optical path length is proportional to the time light needs to travel between two points

    \[ OPL  = \int_{a}^{b} n(s) ds \]

OPL

In a homogenous medium with refractuion index n and physical point distance d this formula simplifies to

    \[ OPL  = n d \]

Optimal Aperture

F# with the largest possible DOF.
Larger F# reduces the DOF due to diffraction

critical and optimal aperture

orthographic

orthographic lenses are a type of fisheye lenses

orthographic lenses are also called” hemispherical“or “orthographisch
orthographic lenses use an image mapping function of type
r = f sin \theta

maintains planar illuminance

orthographic angles
weak medium strong max
66 90 120 180

hemi180[1]

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.

see:
fisheye types