In: Biology
Explain in your own words why you need to turn the brightness of the lamp up when you use an x100 objective compared to an x10 objective
Describe in your own words what depth of field is
Q. Explain in your own words why you need to turn the brightness of the lamp up when you use an x100 objective compared to an x10 objective
Ans. The relationship between Image brighness and magnification is given by:
Image Brightness (Numerical aperture of the objective/ Magnification) 2
As we can see from the above relation, Image brightness decreases by square of magnification. When an objective is changed from 10x to 100x there is a 10 fold increase in magnification which proportionately decreases the image brightness(the image becomes 100 times dimmer)
In other words, The area we are looking under 100x objective is smaller when compared to 10x which obviously means that there are lesser light rays passing through the field and image becomes dimmer
Thus, by increasing the brightness of the lamp helps in better visualization when objective is changed from 10x to 100x.
Q. Describe in your own words what depth of field is?
Ans. The thickness of plane of focus is called as Depth of field. It is also inversely related to magnification i.e., when magnification increases, the depth of field also increases. For example while observing the specimen at lower objective, the entire volume or thickness of the sample is visualized, but when the magnification is increased, only a part of the surface of the specimen is visualized. This is described as Depth of field.
Magnification | Depth of field in micrometers |
10x | 8.5 |
100x | 0.19 |
As we can see from the above table depth of field is greatly decimated to fractions when magnification is increased to 100x.
The relation between depth of field, Numerical aperture, light and magnification is given by:
Depth of field =
Where = wavelength of the illuminating source, n is the refractive index, M is the magnification and e is the smallest distance that can be resolved by the detector