B-500Dk Darkfield Microscope; Principles Of Immersion Microscopy - OPTIKA MICROSCOPES B-500DK Manual De Instrucciones

1.0 B-500DK DARKFIELD MICROSCOPE

B-500DK is a darkfield system specific for blood analysis with a 1.36 - 1.25 N.A. special extra effi-
cient darkfield condenser and a 100X plan-achromatic objective with adjustable iris diaphragm.
The X-LED illumination ensures the high level of light intensity typically needed in high magnification
darkfield techniques.
In order to correctly use this microscope, one has to gain some familiarity with a) oil immersion te-
chnique and b) darkfield technique.
In the following manual we present the basics of these methods (chapters 2 and 3) and then we give
a step-by-step guide to configuration of B-500DK (chapter 4). General tips for immersion microscopy
are also given (chapter 5).

2.0 PRINCIPLES OF IMMERSION MICROSCOPY

The ability of a microscope objective to capture deviated light rays from a specimen is dependent
upon both the numerical aperture and the medium through which the light travels.
An objective's numerical aperture is directly proportional to the refractive index of the imaging me-
dium between the coverslip and the front lens, and also to the sin of one-half the angular aperture
of the objective. Because sin cannot be greater than 90 degrees, the maximum possible numerical
aperture is determined by the refractive index of the immersion medium. Most microscope objectives
use air as the medium through which light rays must pass between the coverslip protecting the sam-
ple and front lens of the objective. Objectives of this type are referred to as dry objectives because
they are used without liquid imaging media. Air has a refractive index of 1.0003, very close to that of
a vacuum and considerably lower than most liquids, including water (n = 1.33), glycerin (n = 1.470)
and common microscope immersion oils (average n = 1.515). In practice,
the maximum numerical aperture of a dry objective system is limited to 0.95, and greater values can
only be achieved using optics designed for immersion media.
Page 3