<P> Before the development of synthetic immersion oils in the 1940s , cedar tree oil was widely used . Cedar oil has an index of refraction of approximately 1.516 . The numerical aperture of cedar tree oil objectives is generally around 1.3 . Cedar oil has a number of disadvantages however : it absorbs blue and ultraviolet light , yellows with age , has sufficient acidity to potentially damage objectives with repeated use ( by attacking the cement used to join lenses ) , and diluting it with solvent changes its viscosity ( and refraction index and dispersion ) . Cedar oil must be removed from the objective immediately after use before it can harden , since removing hardened cedar oil can damage the lens . In modern microscopy synthetic immersion oils are more commonly used , as they eliminate most of these problems . NA values of 1.6 can be achieved with different oils . Unlike natural oils synthetic ones do not harden on the lens and can typically be left on the objective for months at a time . </P>
different types of oils that can be used with an oio lens
cedar tree oil synthetic immersion oils