Magnification and calibration - 2.2 (3) Flashcards
Module 2, Chapter 2, 2.2, Page 16 & 17
To measure the size of a sample under a microscope, what do you use?
an eyepiece graticule
What can the true magnification of the different lenses of a microscope vary slightly from?
the magnification stated
Every microscope and every lens has to be…
calibrated individually using an eyepiece graticule and slide micrometer
What is an eyepiece graticule?
a glass disc marked with a fine scale of 1 to 100
What has no units and remains unchanged whichever objective lens is in place?
the scale
The relative / proportionate size of the division increases with each…
increase in magnification
What do you need to know in order to measure specimens?
what the divisions represent at the different magnifications
What is calibrated using a stage micrometer?
the scale on the graticule at each magnification
What is a stage micrometer?
a microscope slide with a very accurate scale in micrometres engraved on it
The scale marked on the micrometer slide is usually…
100 divisions = 1mm
1 division = …
1 micrometre
What do you calibrate for each objective lens and how?
the eyepiece graticule scale seperaretly
What happens once all three lenses are calibrated?
if you measure the same cell using the three different lenses you should get the same actual measurement each time
Example: What happens first in calibrating a x4 objective lens?
put the stage micrometer in place and the eyepiece graticule in the eyepiece
Example: What occurs after you put the stage micrometer and eyepiece graticule in place?
get the scale on the micrometer slide in clear focus
Example: What happens after you get the scale on the micrometer slide in clear focus?
align the micrometer scale with the scale in the eyepiece
Example: 30 divisions on the eyepiece graticule = …
10 divisions on the stage micrometer
Example: 100 micrometer divisions =…
1mm
Example: How much is each small division?
0.01mm
Example: 30 graticule divisions = how many micrometre divisions?
10
Example: 10 micrometre divisions = how many micrometres?
10 x 10 = 100 micrometres
Example: 1 graticule division = …
number of eyepiece divisions / number of micrometres
Example: 30 graticule divisions =…
100 micrometres so 1 graticule division = 100/30 = 3.33 micrometres –> the magnification factor
Example: What do you have to do in order to use the magnification factor?
remove the stage micrometer and place a prepared slide on the stage
Example: Measure the size of an object in…
graticule units
Example: To find the actual size multiply the number of graticule…
units measured by the magnification factor to give you the length in micrometres
Example: graticule divisions x…
magnification factor = measurement (micrometres)
e.g., the diameter of a cell seen using the x4 objective lens measures 10 graticule divisions. Each graticule division = 3.33µm so the cell diameter…
= 10 x 3.33 = 33.3 µm
