In conventional fluorescence microscopy the inside structure of a thick specimen cannot be observed clearly because of the significant contribution of out of focus light from above and below the focal plane. The disc scan unit (DSU) makes it possible to reject this out of focus light by placing a rotating slit disc in a confocal plane of the microscope. The result is a clear, continous, optically cross-sectioned image, that can captured at up to 30fps with a cooled CCD camera. Every image acquired by the camera has the DSU confocal effect alleviating the need for post image processing, thus improving data reliability for 3D images.