FIG. 4.

Brightfield and confocal microscopy. (A) The optical path of a bright field microscope includes uniform illumination of a sample. Light from the focal plane as well as from the out-of-focus planes of the objective reaches the detector. (B) The optical path of a confocal microscope relies on focused illumination of a point on the sample, which is then imaged onto a pinhole in front of the detector. Most of the light emanating from the out-of-focus planes does not reach the detector because of the pinhole. (C) Transmission image of a silk scaffold including signal emanating from various planes along the specimen. (D) Corresponding confocal fluorescence image of a silk scaffold, illustrating optical sectioning (bar = 75 μm, magnification: 63× water immersion objective).