(usually horizontal) extend of an object that’s visible on a sensor.
Sometimes the HFOV (horizontal field of view), sometimes the VFOV (Vertical Field of View) and sometimes the DFOV (Diagonal Field of View) matters. It’s of utmost importance to state clearly which matters.
is the study of perfect optical systems.
Any imperfections and aberrations, also wavelengths, diffraction, interference etc. are ignored.
Parts of first order optics are Gaussian optics ( = paraxial optics).
Results of this analysis are image location and magnification.
Compare third order optics