Calibration of Microscope : Pharmaceutical Guidelines

# Calibration of Microscope

Learn how to calibrate the Microscope using low power objective, high power objective and oil immersion objective.
1  Calibration frequency quarterly.
2  Remove the plastic cover of Microscope, and clean with lint free duster
3  Remove the eyepiece (ocular) lens from microscope, unscrew it and insert the ocular micrometer disc on the circular shelf with the engraved side down into it.
4  Screw the eyepiece back and insert it in the microscope.
5  Switch “ON” the microscope and operate as per the Operation of Microscope.
6  Place the stage micrometer slide on the microscope stage and bring its scale in the microscope’s field center under a sharp focus first using the low power objectives, and thereafter with high power and oil immersion objectives.
7  Turn the ocular lens until the parallel lines of the ocular micrometer be parallel with those of the stage micrometer.
8  Make the lines coincide at the left end and find another line set which coincide.
9  Now count the number of distances (division), in both the ocular and stage micrometer, between the two coinciding lines.
10  Take at least six reading at random repeating the above steps.
11  Repeat steps with high power and oil immersion objectives.
12  Record your observation. Take the mean of six readings taken for the ocular micrometer coinciding with stage micrometer divisions each for low power, high power and oil immersion objectives.
13  Determine the value of calibration factor for different objective lenses as follows-
a)  Low power objective (10 X 10 i.e. 100 X magnification):
Suppose, 20 ocular micrometer division = 30 stage of micrometer division
1 division of ocular micrometer (1 O.D.) = 30/20 X 10
= 15 mm
b)  High power objective (10 X 40 i.e. 400 X magnification):
Suppose, 24 ocular micrometer division = 9 stage of micrometer division
1 division of ocular micrometer (1 O.D.) = 9/24 X 10
= 3.75 mm
c)  Oil immersion objective (10 X 100 i.e. 1000 X magnification):
Suppose, 20 ocular micrometer division = 3 stage of micrometer division
1 division of ocular micrometer (1 O.D.) = 3/20 X 10
= 1.5 mm
14  After calibration, immediately put the “CALIBRATION” tag duly filled with necessary information.
15  Calibration factor must be considered during routine analysis i.e. particle size determination.
Precaution
1  Observe the slide with both the eyes open to have less strain on your eyes.
2  Keep the microscope and its parts clean and handle all parts with care.
3  Glass parts should not be touched with finger.
4  Always keep the microscope covered when not in use.
5  Never use a slide without cover slip while examining an object under high power of the microscope; otherwise the chemicals will damage the objective.

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.

#### 1 comment:

1. Anonymous23/4/11 11:04

Calibration of Microscope is done at the initial stage only .There is no need to calibrate the Microscope if there is no change in the optical tube length,focal length of the objective and magnifying power of the eye piece.If any one of these is changed carry out the calibration.

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