Refurbished Microscope Objectives for reflected light microscopy
The objective lens
This is the most important single optical component in the system for it fulfils the following criteria
Controls the resolution of the image
Controls the magnification of the image.
Forms the primary image
The objective lens requires a large numerical aperture at the same time as having a small field of view.
The Numerical Aperture (NA) of a lens is a function of the maximum angle of light a lens can accept from the object plane that defines the light collection capability of the lens.
The NA can range from 0.05 for low power lenses at 1.4 x up to 0.95 ( the maximum NA for air lenses) for dry lenses at 60X Oil immersion lenses can have an NA of 1.4 for magnifications between 40 and 100X.
A nosepiece of a typical metallurgical microscope has four objective lenses that are parfocal – ie. all have an equivalent focal plane on rotation of the nosepiece.