# Microscope Objective Parameters. What do the Numbers on the Objective Mean ?

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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 Magnification 2 §How many times is the image bigger than the object being viewed ?

Colour ring §The 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 NA 2  NA = n.sin(    is the half angle of view for the lens §n 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 Medium §This 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.

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