Micrometry is the measurement of microscopic objects using a micrometer attached to microscopes. The micrometer was invented by William Gascoigne and improved by Robert Hooke. Microscopic measurements are performed in the range of 0.2μ to 25μ. A stage micrometer provides a standardized scale against which an ocular micrometer can be calibrated at different magnifications. The camera lucida is an optical device that projects the microscope image onto a surface, allowing accurate outline drawings to be made at the correct scale and proportions.

1. MICROMETRY
AND
CAMERA LUCIDA

2. •MICROMETRY
The field of science dealing with the measurement of microscopic
objects using micrometer is called micrometry or morphometrics .
•While studying microorganisms , it is often necessary to measure their
length,breadth,diameter etc . This can be done with the help of a device
called micrometer.
•MICROMETER Greek-micro(µ): small ,meter : a measure
Micrometer is an instrument attached to microscopes for measuring
dimensions of small objects.
•WILLIAM GASCOIGNE invented the micrometer. Robert Hooke
improved Gascoigne’s micrometer by substituting parallel hairs for the
parallel edges.
•Microscopic measurements were first performed in the late 1600s by
Anton Von Leeuwenhoek, who used fine grains of sand as a gauge to
determine the size of human erythrocytes.

3. • Microscopic measurements are in the range of the average field
diameter of wide field eyepieces i.e. 0.2µ -25µ.
• Measurements below 0.2µ are beyond the resolving power of the
microscope.
• Lengths larger than the field view of wide field eyepiece are usually
measured with stereomicroscopes.
• The measurements are expressed in mm, µm (light microscope) or
nm(EM).
• The parameters that can be measured are : length(linear),
thickness(volume), area and angles.

4. COMPONENTS OF MICROMETER
1)Stage micrometer
2)Ocular micrometer
Stage micrometer is a microscope glass slide at the centre of which has
a very finely graduated scale measuring 1mm.This line is divided into 10
equal divisions by small lines with longer lines marked as 0,1,2,3…and so
on. Each of these divisions is subdivided into10 equal divisions by small
lines. Thus 1mm is divided into 100 equal divisions and hence the
magnitude of each division is 0.01mm
Ocular micrometer/Eye-piece micrometer/Eye-piece reticle
Ocular micrometer is a transparent circular glass disc which is placed in
the body of ocular lens(eye piece) of the microscope. In the centre of the
OM a line is drawn. This line is subdivided into 100 equal divisions, as in
the case of the stage micrometer. Graduations of eyepiece scale are
referred to as reticle.
However ,the scale on ocular micrometer does not have any
standard value. When the OM is placed in the eyepiece, the ruled lines
superimpose the SM divisions

6. CALIBRATION OF OCULAR MICROMETER
Micrometric calibration involves finding out the absolute
magnitude of each division of the OM scale with respect to the
magnitude of the SM division. This value is called micrometer
value, or calibration factor. Calibration can be done only after super
imposing the graduations of both stage and ocular micrometers.

7. 1 division in ocular = number of divisions on stage micrometer
number of coinciding divisions on ocular
micrometer
One stage division=0.01 mm or 10µ
ADVANTAGES OF MICROMETRY
 Best method for measuring microorganisms.
 Best method for taxonomic measurements.

8. PROCEDURE OF MICROMETRY
1. Standardization of ocular micrometer using stage micrometer.
2. Find the value of 1 ocular division( eg:25µ).
3. Remove stage micrometer and place object slide.
4. Measure the object using ocular scale.
5. Calculate the actual size.
e.g. Suppose mean length and breadth of a cell is 4.2 and 2.5 ocular
divisions
Length =4.2×1 ocular value
=4.2×25
=105µ
Breadth=2.5×1 ocular value
=2.5×25
=62.5µ
Size of the cell=105µ×62. 5µ

9. Let the no. of division on the stage micrometer be y and the no. of
divisions on the ocular micrometer be x.
Since each stage micrometer divisions is 0.01 mm apart, the distance
between the starting point and point of coincidence on ocular and stage
micrometers can be calculated at that magnification.
In other words:
Distance covered by x no. of OM = Distance covered by y no. of SM
divisions divisions
Since1SM division is 0.01 mm,
the distance covered by x divisions of OM = y divisions × 0.01mm
Therefore, 1 OM division = y division × 0.01mm
x division

10. Suppose 10 OM division (x) overlaps 7 SM divisions (y) at 40x
magnification
1 OM division= stage × 0.01
ocular
= 7 × 0.01
10
= 0.007 mm
Therefore calibration is the process of determination of the
magnitude of one division of the ocular micrometer at a particular
magnification with the help of a stage micrometer. Here the
values of ocular micrometer division is calibrated as0.007 mm.

11. CAMERA LUCIDA
Camera Lucida was developed by Wollaston for making drawings of
microscopic objects used along with microscope.
This is an accessory instrument.
DEFINITION: It is a simple optical device which enable the
observer to make reasonably accurate outline drawings of correct
scale and proportions of objects seen under the microscope.
OR
It is an instrument ,mounted on the top of the body tube of a
compound microscope for making clear, simple and exactly
proportionate outline sketches of the objects under study.

12. CAMERA LUCIDA

13. CAMERA LUCIDA-PARTS
Mirror ,Reflecting prism
Mirror:Adjustable,inclined at 45º both to the desktop and the prism.
Prism: surface is silvered. The particular central area that coincides
with eyepiece is not silvered.
PRINCIPLE: deflection/reflection of light
a) The light rays passing through the ocular lens are deflected at 90 by
the prism.
b) These rays are further deflected at90 by the mirror.
c) This arrangements give a virtual image on the desktop beside the
microscope. If a piece of paper is kept there, the viewer can see and
draw that image.
d) Magnification is due to the angular deviation

15. ADVANTAGES
Gives accurate sketch of the microscopic objects.
The outline sketch is a magnified version of original
object on the slide.—Tracing of outline is an easy task.
HISTORY
The camera lucida was patented in 1807 by William
Hyde Wollaston.
The basic optics were described 200 years earlier by
Johannes Kepler in his Dioptrice (1611), but there is
no evidence he or his contemporaries constructed a
working camera lucida.
By the 19th century, Kepler’s description had totally
fallen into oblivion, so Wollaston’s claim was never
challenged.

16. CALCULATION OF MAGNIFICATION
It is computed by multiplying the power of the eyepiece
and the objective lens used.
1) Focus the stage micrometer at the center of the field of
observation.
2) Draw a few division with the help of the drawing prism
3) For more accurate result, take 2 more drawings at the left
and right side of the field of observation.(Because the
magnification varies according to the position of the stage
micrometer, greatest at the left and lowest at the right)
4) Measure the drawn divisions by a mm scale
Calculate magnification as follows :
e.g. 1 magnification stage division= 5 mm (1 mm=1000µ)
i.e.,10µ is magnified to 5x1000µ=5000µ
`.` 1µ is magnified5000 =500
10
So the magnification is 500 times.