Notation according to DIN 1335 and DIN 4522:

Focal length f ', F'
Front focal length SF
Back focal length S'F'
Principal point / Nodal point separation HH ' (+) Front nodal point is to the left of the rear nodal point
(-) Front nodal point is to the right of the rear nodal point
Pupil magnification 'P Diameter of exit pupil / Diameter of entrance pupil
Entrance pupil Position Sep Distance from Front Glass Vertex to Entrance Pupil
Exit pupil position S'ap Distance from Rear Glass Vertex to Exit Pupil
Overall optical length Σd Distance from front vertex of first lens to rear vertex of last lens
Image to Object distance OO' Total length from image plane to object plane
Magnification ratio ' u'/u
Object Height u 1/2 actual object height
Image Height u' 1/2 actual image height

*All distances are measured from left to right.