A
- Abbe
- Abbe number
- absorptance
- absorptive lens
- Active ophthalmic instrument
- addition power
- additive power trial case lens set
- Adjusting rail
- afocal lens
- aid microscope
- aid telescope
- alignment reference marking
- angular magnification
- antireflection coating
- apex
- apical angle
- arm
- as-worn power
- aspheric lens
- aspherical surface
- astigmatic difference
- astigmatic effect
- astigmatic lens power
- astigmatic power lens
- astronomical telescope
- atoric lens
- atoroidal surface
- auxiliary beam
- auxiliary lenses
Abbe number
Mathematical expression for determining the correction for chromatic aberration of an optical material of component expressed as either: "formular" where nd is the refractive index of the yellow helium d-line (wavelength: 587,56nm).