System4f.frontFocalLength

raytracing.System4f.frontFocalLength(self)

The focal lengths measured from the front vertex. This is the distance between the surface and the focal point. When the principal plane is not at the surface (which is usually the case in anything except a thin lens), the back and front focal lengths will be different from effective focal lengths. The effective focal lengths is always measured from the principal planes, but the BFL and FFL are measured from the vertices.

Returns:: frontFocalLength – Returns the FFL
Return type:: float

Examples

In the following example, we have defined an object(f=5) with physical length of 4. And the front vertex is placed one unit before the front principal plane. There for the front focal length will be 4.

>>> from raytracing import *
>>> # M1 is an ABCD matrix of a lens (f=5)
>>> M1= Matrix(A=1,B=0,C=-1/5,D=1,physicalLength=4,frontVertex=-1,label='Lens')
>>> FFL=M1.frontFocalLength()
>>> print('the front focal distance:' , FFL)
the front focal distance: 4.0