User Guide

490 Series Microscope
AmScope Proprietary Page 62 of 64
Numerical Aperture (N.A.)
N.A. is a rating for the resolution of the objective lens. The N.A. rating ranks the
objective lens’ ability to capture light and show fine detail.
Lens with larger numerical apertures capture finer details than lenses with smaller
numerical apertures. Generally, lenses with larger numerical apertures create a brighter
image, but the depth of field will be shallower.
N.A. Rating
Objective
Lens
Average
Numerical
Aperture
4X 0.1
10X 0.25
40X 0.65
100X 1.25
Parcentered
When changing objectives, the image of the specimen stays centered. Most compound
microscopes are parcentered.
Parfocal
When changing objectives, the image of the specimen stays in focus without
needing to adjust the coarse focusing knob. Not all compound microscopes are
parfocal.
Phase Contrast
Many biological specimens are virtually transparent when viewed with a typical
compound microscope. Phase contrast microscopy is a method that collects light from
specific incidents (phases) of light only to allow better contrast in viewing transparent
specimens.
Phase Contrast improves visibility by manipulating direct and diffracted light to produce
greater contrast without losing resolution. The major benefit is the ability to study living cells
in their natural state instead of killing them with stain.
Brightfield Phase Contrast