Assume that light of wavelength `6000Å` is coming from a star. What is the limit of resolution of a telescope whose objective has a diameter of 100 inch

Light of wavelength 589 nm is used to view an object under a microscope. The aperture of the objective has a diameter of 0.900cm. What is the limiting of resolution of the above microscope?

Light of wavelength 589 nm is used to view an object under a microscope. The aperture of the objective has a diameter of 0.900cm. What happens to the limit of resolution if the objective is immersed in oil? Explain.