I am using a Renishaw inVia confocal microscope to study emission spectrum of molecules. The excitation wavelength of laser that I use is 532nm. However, I met with a very basic problem. When I use the same material (say plain silicon), and use different objectives (20X, 50X, 100X), then I will get totally different emission spectra. The spectra from each objective are consistent. My understanding is that the emission spectrum should definitely not change when I use different objective. This is driving me crazy. Any possible explanations?