L6 Thick Lens Flashcards
define lens system
optical systems that consist of more than one lens/refracting system
define thick lens
a lens that may not be considered thin because of centre thickness
state and explain two methods to solve optical systems with thick lens or multiple lens system
- element by element: each surface/lens is imaged separately, for simple systems (uses same relationships in single refracting surfaces)
- cardinal points: COMBINE surfaces/lenses into one system, redefine planes and powers, more calculations required
explain front focal length
distance from front surface of a lens or first element of an optical system to the primary focal point of the system
explain back focal length
distance from back surface of a lens or last element of an optical system to the secondary focal point of the system
explain how primary and secondary focal lengths work in thick lens & lens system
not measured from surface, but measured from principal planes. principal planes are conjugate planes.
- primary focal length (H) measured from first principal plane (formed by parallel emergent ray)
- secondary focal length (H’) measured from second principal plane (formed by parallel incident ray)
explain back vertex power
The emergent vergence from the back surface of a lens or the last element of an optical system for an object placed at infinity (Fv = n3/bfl)
The effective power of the front surface at the back surface plus the power of the back surface gives the back vertex power
explain neutralising power (Fn)
the effective power of the back surface at the front surface plus the power of the front surface gives the neutralising power
explain principal points
- the intersection of the first principal plane and optical axis: first principal point
- the intersection of the second principal plane and the optical axis: second principal point
explain nodal points and a scenario
nodal points are 2 points where undeviated ray will pass through and there will be lateral displacement
when an incident ray is aimed at the first nodal point, it refracts at the front surface then passes through the optical centre and then leave the back surface as if it is coming from the second nodal point
explain relationship between oc and nodal points
there is no deviation between the incident ray and the emergent ray but there is lateral displacement
the nodal points are actually the position of the optical centre when viewed from the front and back of the lens
explain further on optical centre
independent of the refractive index of the material
it is the only point in an optical system that is independent of the wavelength
