<P> The refractive indices of the oil and of the glass in the first lens element are nearly the same, which means that the refraction of light will be small upon entering the lens (the oil and glass are optically very similar). The correct immersion oil for an objective lens has to be used to ensure that the refractive indices are correctly matched . Use of an oil immersion lens with the incorrect immersion oil, or without immersion oil altogether, will suffer from spherical aberration . The strength of this effect depends on the size of the refractive index mismatch . </P> <P> Oil immersion can generally only be used on rigidly mounted specimens otherwise the surface tension of the oil can move the coverslip and so move the sample underneath . This can also happen on inverted microscopes because the coverslip is below the slide . </P> <Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (January 2008) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (January 2008) </Td> </Tr>

Function of the high power objective on a microscope