The principle how SAF Microscopy works is as follows: A fluorescent specimen does not emit fluorescence isotropically when it comes close to a surface, but approximately 70% of the fluorescence emitted is directed into the solid phase. Here, the main part enters the solid body above the critical angle. When the emitter is located just 200 nm above the surface, fluorescent light entering the solid body above the critical angle is decreased dramatically. Hence, SAF Microscopy is ideally suited to discriminate between molecules and particles at or close to surfaces and all other specimen present in the bulk.