|
'Optical centre' has two other meanings, altogether.
In optometry it refers to the spot on a lens where the front and back surfaces are plane parallel. When the lens is trimmed to fit a frame, the lens is arranged so that this point coincides with the wearers line of vision when looking straight ahead.
In optical manufacturing it also refers to the same spot on a lens where the surfaces are plane parallel. 'Optical centring' refers to a process where a lens is mounted on a spindle using soft pitch, and as it rotates slowly, the lens is shifted laterally to place the optical centre on the axis of rotation. The lens is then 'edged', ie the edge ground off, the result being a lens that has no wedge. This is used in the manufacture of objective, eyepiece and camera lenses. Optical centring is also used to align the elements before the are cemented.
The optical centre of a lens can be seen while it is rotating on a spindle by shining a light at it, looking down from above. If it is off the axis of the spindle, the spot will wobble from side to side visibly.
Hence as I indicated earlier the term has different meanings according to the context; if you really mean the focus or centre of curvature, better to refer to them as such.
|