Page 92 - Practical Technology 2025

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Clinical Pharmacy-Pharm D Level Three 2 Semester 2024/2025 Pharmaceutical Technology (PT 607)

✓ The microscope eyepiece is fitted with a micrometer by which the size of
the particles can be estimated.
✓ The ordinary microscope used for measurement the particle-size in the

range of 0.2 to about 100 µm.

Resolving Power (limit of resolution) of optical microscope:

The minimum distance existing between two objects when these objects can still

be observed as separate objects.

d= (0.61 x λ)/ NA

d= resolving power

λ = light wavelength that used to illuminate the specimen

NA= numerical aperture

Factors affecting Resolving Power (limit of resolution):

1. Numerical aperture

2. λ

Numerical Aperture

The arithmetic product of the refractive index of the medium in which the
objective lens is situated and half the angle of cone of light entering an objective
NA= n Sin ϴ

How can I increase NA?
Decreasing working distance will increase the value of ϴ, and on turn NA will
increase.

Increasing n by using oil as a medium for objective lens n of oil is higher than
water and air.

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