What iscondenser lensin microscope

The maximum possible depth of field is obtained when the lens is focused one focal length f farther than the hyperfocal distance H: everything between Dn and infinity will be sharp. The value "Infinity" can be entered for Df, but since it's case sensitive it has to be typed as shown.

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Of course, all distances are measured from the lens front and rear principal points respectively. Too often, unfortunately, these points are not specified by the lens manufacturer: it's hard to guess their position, since they can be anywhere inside or outside the lens. Anyway, the rear principal point is always one focal length ahead the sensor * when the lens is focused at infinity. The location of the front principal point cannot be neglected when using macro lenses.

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Condenser lensfunction

With this tool you can calculate the required focal length to take a picture of an object at a given distance in order to generate an image fitting on your sensor size.

Please note: All calculations are based on theoretical formulas only, assuming the principal planes are identical. Actual results will differ! Our sales team will be happy to assist you!

Condenser lensin electron microscope

The hyperfocal distance H is the minimum distance from the front principal plane that will appear sharp when the lens is focuses at infinity (xo = infinity).

The condenser lens is a lens that controls the probe current and probe-diameter by a combined use with the objective aperture. As shown in Figures below, when the lens excitation is strong, the number of electrons passing through the objective aperture is small, whereas when the excitation is weak, the number of electrons passing through the aperture is large. Furthermore, when the lens is strongly excited, the focal length of the lens becomes short, and thus the electron probe size becomes small. Therefore, the probe current and probe diameter are controlled by the condenser-lens excitation. Normally, the condenser lens is strongly excited for high-resolution image observation to obtain a small probe size, and weakly excited for analysis such as EDS to obtain a large probe current. An SEM equipped with a thermionic-emission gun uses the multi-stage condenser lens system to control the probe diameter in a wide range. Since the crossover (electron source) of this gun is as large as 20 µm, the crossover needs to be demagnified to about 1/1000 with a high reduction rate. An SEM equipped with a Schottky-emission gun has an electron source as small as 15 to 20 nm, and thus the lens with a low reduction rate is allowed. An SEM equipped with a field-emission gun has a sufficiently small source size. Thus, the condenser lens is mainly used to control the probe current with a one-stage condenser lens because the control range is small.

The circle of confusion c is the diameter of a circle on the image plane that can be considered a single point when the image is observed (the size of the film/imager is different that the size of the print/screen. For 35 mm photography c is usually 0.025 mm, but this value depends of course on the size of the final prints.