Resolution

Resolution, also referred to as resolving power, describes the ability of an imaging system to resolve detail in the object that is being imaged. The smaller the object that an imaging system can resolve, the higher its resolving power. The resolution can be calculated by dividing the wavelength by the 2*numerical aperture, which is a constant determined by the lens. Resolution can be increased by increasing the numerical aperture number or decreasing the wavelength. For example, using purple light (~400nm) will result in a higher resolution than using red light (~800nm).

Light Microscope
The light microscope can have a maximum magnification of 2000x with a 20x ocular and a 100x objective, but the microscopes in our lab have the 10x ocular. The reasoning behind the 10x ocular is the limiting factor of the resolving power. Even if the specimen can be magnified to 2000x, the image would be blurry and undesirable.

The 100x oil immersion lens requires use of oil to decrease light refraction and increase resolution. If there is no oil, the resolution decreases, and the size of the smallest thing you can see increases. Under the best conditions, the smallest object the light microscope can resolve is 200nm, which is 1000 times better than the human eye.