Microscope Objective Parameters

What do the Numbers on the Objective Mean ?

PLAN

This means that the focal plane of the objective is flat

Apochromat

If there is no indication, the lens is either Achromat (corrected at two wavelengths) or has no correction.

An apochromat objective has its focal length corrected at three wavelengths across the visible spectrum.

Magnification

Light loss is proportional to Magnification2

How many times is the image bigger than the object being viewed ?

Colour ringThe coloured rings on an

objective indicate its magnification

Black = 1x Grey = 2x Red = 4x Yellow = 10x Green = 16x, 20x Light Blue = 40x, 50x Cobalt Blue = 60x, 63x White = 100x

Half angle of View

is the half angle from the focus point to the edge of view for the lens

It determines how much light the lens needs to “see” an object.

Numerical Aperture (NA)

The light gathering capacity of the lens is proportional to NA2

NA = n.sin(is the half angle of view

for the lensn is the refractive index of

the immersion medium.

Tube Length

Typical values are 160 mm and infinity It is a microscope parameter.

This is the distance from the rear focal plane of the lens to its image plane.

Cover Glass Thickness

This is the recommended thickness of the cover glass to use with the objective.

A very popular value is 0.17 mm.This size is also known as size 1.5

Working Distance

This is the distance from the lens tip to the top of the cover glass

Immersion MediumThis is the recommended

immersion medium for the lens

Typical substances are oil, water and glycerol

No indication means the immersion medium is air

Application Markings

This indicates the application for the lens.

Examples are DIC for differential interference contrast, DL, DLL and DM for various phase contrast applications.

Collared Lenses

Some objectives have adjustable collar rings.

These can correct for a variety of cover glass thickness and immersion media.