Origin of unexpected condenser-like rings observed in Fourier plane images obtained using immersion-oil objective lenses

I show that different setups for bright field optical microscopy which are usually used in biomedical laboratories behave like efficient microscope condenser that are responsible for the observed sub -wavelength resolution. We present a series of experiments that reveal how inclined illumination from such unexpected condensers occurs when the sample is being perpendicularly illuminated by microscope’s built-in white -light source. In addition, using low numerical aperture objective lenses in combination with the Fourier Plane Imaging Microscopy technique, we demonstrate the possibility of fabricating an inexpensive add-on optical module that can serve as an efficient and light -weight microscope condenser.