Hellooooooo world, how are you all? i hope you are doing great and good and i am too. I didn't get time to make post from last two weeks because i was sick. Today we will focus on microscopic specifications and what its role.
First of all i want to tell about what are the parts of a microscope. Microscope has ocular lens from where we will see and objective lens is where we will change for magnification like 4X, 10X and 40X. Total magnification is multiplication of eyepiece magnification and objective magnification. It means eye piece magnification will be 10X and objective magnification will differ and most of the times mitosis is counted at 40X objective magnification and so total magnification will be 400X magnification.
Here we have to know that when we see through microscope we will see field area as circular. So we need to calculate the area for that specific objective magnification.

Every microscope on its eye piece there will be labelling of eye piece magnification of 10X and field number 20, 22 etc. Field number differs for different microscope. Presently 20 and 22 are the field numbers most commonly we will see on the microscope.
Now we have to calculate field diameter and field area.
To get field diameter the formula is Field number/Objective magnification = Field diameter.
In our case Field number - 22
Objective magnification - 40
Field number/Objective magnification - 22/40=0.55mm
Now we got Field diameter which is 0.55. Now divide it by 2 we will get 0.55/2= 0.275.
Now lets calculate the field area, we know the field area looks in circular shape. So the formula for area of circle is πr². So 3.14x(0.275)²= 0.24 mm².
So Field area is 0.24 mm². So one field area with 22 field number is 0.24mm2. so for 1 mm² how many field are required? Then we have to divide 1/0.24= 4.16 so approximately 4 fields if we want to see in 2mm² area then it will be 8 to 9 fields.
So this is how we have to calculate. Suppose if we got 11 mitosis in 4 fields for the microscope having 22 field number, then we have to write 11/mm². So depending upon number fields the field area will changes. So basically what i want to convey is field area depends on field number. The more is the field number the more will be the cost of microscope too. So the price of the microscope depends on field number too.

Simplified manner

Field number - 22

Objective magnification - 40X

Field diameter - 0.55 mm

Field area is πr² = 3.14×0.275×0.275= 0.24 mm²
One Field area = 0.24 mm²
1 mm² = 4 fields
2 mm² = 8-9 fields
This is for the microscopes which are having field number 22.

your turn - Lets try this

This is the field number of this microscope. Calculate the field diameter and field area for this microscope at 40X objective magnification.
Hope you understand this one.

References

• Bancroft’s Theory and Practice of Histological Techniques (8th Edition)

Thanks for reading,
With regards,