Conjugate focal planes

The schlieren microscope is able to detect refractive index variations to six decimal places. Any small difference in optical path (index difference, film thickness, etc) is very precisely detected by the schlieren microscope, especially in the Dodd modification. It is, in effect, a darkfield method. The specimen is illuminated with light in a portion of the illuminating cone and that direct light is masked in the conjugate back focal plane of the objective (Fig. 3). The only light to pass through this plane is refracted, reflected, or diffracted by the specimen. 

Fig. 2 Schematic diagram of laser optical tweezers (LOT) system. (Top panel) An infrared laser beam was steered to trap and move pm-size particles in the focal plane. At a sufficiently large laser intensity, the gradient force dominates over the scattering force. (Lower panel) Membrane tethers are extracted from live cells. Dielectric beads (0.5 pm in diameter) were conjugated with antibodies against integiins and attached to the cell membrane. LOT traps one bead and pulls it away from the cell, as indicated by the arrow. Thin membrane tethers extending from the beads to the cell body appear. Using conventional brightfield microscopy, the tether length and its diameter are measured which, in turn, provide an estimate of the plasma membrane tension.

The complete diffraction diagram, which appears at the back focal plane of an electronic objective lens, is actually a mapping of the Fourier transform of the specimen [1, 2]. An object point usually is displaced from its true conjugate point by an amount due to defocus (Az) and the spherical aberration coefficient (Cs) giving rise to a total displacement on the TEM image of ... 

Conjugate focil n. In an image-forming system, two fields are said to be conjugate with each other when one or more object fields are simultaneously in focus in a single plane, e.g., in Kohler illumination the field diaphram, specimen and ocular front focal plane. 

The circular spot of light formed at that distance above the eyepiece where the chief image forming rays cross the back focal plane of the eyepiece. The objective back focal plane is in conjugate focus in this... 

Planes constructed at the focal points perpendicular to the optical axis are called focal planes. Parallel rays, even if not parallel to the axis, intersect in the focal plane. Corresponding points in the object and image space— points that satisfy an object-image relation—are called conjugate points. Planes within the points are conjugate planes. The distances between conjugate points and the surface are called conjugate distances [2]. 

Compared to conventional microscopy, confocal microscopy delivers superior optical sectioning by using a pinhole in a plane conjugate with the focal (xy) plane. It allows a crisp 3D image to be built from a stack of 2D images even for somewhat turbid samples, but each 2D image is acquired by scanning, which imposes limits on acquisition speed. The technique has been described in detail before [82]. 

Instrumentation. In a typical CLSM experiment, a narrow laser beam scans a surface horizontally, i.e. at constant height, in x- and y-directions using piezo-driven mirrors. A small pinhole is located in front of an optical detector at a position conjugate to the focal point in the sample plane. This way, the detector measures the intensity of light reflected from the surface at every scanned position. Light scattered from out-of-focus positions is focused outside the pinhole and thus does not reach the detector. An image of scattered and/or reflected laser light intensity is created... 

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