I began to learn Fu ye optics,When you see the concept, don't you know what it means?
That's right upstairs,In paraxial optical calculations, it is usually assumed that theta =sin theta simplifies some calculations
COS 0 = 1, of course this is set as the basic easy calculation, which brings calculation imprecision, produces spherical aberration, astigmatism and distortion of the so-called aberration, 1 degrees angle obviously extreme, generally less than 10 degrees are considered to be near axis or off-axis.
Paraxial optics is set all optical conditions of basic formula, SIN = theta theta meet,
