Why is important to gel all of the oil off the 100x before putting the microscop

Generally when you magnify something so great, the specimen you want to look at is in some water. So the light must go from the liquid the specimen is in, to plain air, then into the lens. Light bends when it leaves water, and since the magnification is so great the bending and distortion of the light ruins the image making it too blurry to see.

SO what the oil does is you put it on top of the cover-slip so the lens is touching the oil. Therefor the light never has to go into the air, it always stays in a liquid and the bending (distortion) is reduced to almost no distortion.

Immersion oil touches the objective lens and it forms another lens. The refractive index of the oil is equal to that of the glass from which the objective lens is made up of. So it just goes well with the objective lens. It further magnifies the object.

Without oil, the light would refract to such a degree that the resolving power would be extremely poor. The oil helps by directing the light into the objectives increasing resolution...