Question

What is the field of view of the 40x objective if the 4x objective has a field of view of 2mm?

A.) 0.2mm

B.) 0.5mm

C.) 0.3mm

D.) 0.1mm

E.) 0.4mm

Answer 1

Answer: option (A) is the correct answer. If the 4x objective has a field of view of 2 mm, then field of view of the 40x objective will be 0.2 mm.

The field of view is defined to be the visible circle of the slide seen while looking through microscope. The original diameters of field of view (FOV) were determined with a transparent mm ruler under low power.

As we continue to increase the magnification of microscope, FOV begins to decrease. The use of a ruler may no longer be possible because you cannot see the scales. If you know the diameter of the FOV at one magnification, you can determine the diameter of FOV at another magnification with the following formula:

FOV # 2 = FOV # 1 x magnification # 1 / magnification # 2

Before you can use this equation, however, you will need to determine the microscope magnification at different power. The magnification is how many times, the object has been enlarged. To calculate the magnification, you will need to multiply the magnification of the ocular lens with the magnification of the objective lens as written in formula below.

Total magnification = Objective magnification X ocular magnification

If Ocular of microscope was used: 10x

Objective 1: 4x

Objective 2: 40x

Total magnification of # 1 = 4x * 10x

                                                = 40x

Total magnification of # 2 = 40x * 10x

                                                = 400x

FOV # 2 = FOV # 1 x magnification # 1 divided by magnification # 2

               = 2 mm X 40x / 400x

              = 80 / 400 mm

            = 2 / 10 mm

            = 0.2 mm