Figure 3
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a) The test object is a stainless steel screw turned upside down, with a diameter of 3.9 mm and a depth of L = 10 mm (not including the screw head). b) Digital-holographic hypercentric reconstruction of the object. The insert shows an image of the centered aperture with diameter d = 0.8 mm. The featured visible object depth is approx. 8 mm. Concerning the amount of hypercentricity we get a measured perspective spread of
, which is in very good accordance with the expected theoretical spread of
. c) From the same holographic data can also be calculated the conventional numerical reconstruction of the hologram. This yields a sharp image of the bottom surface of the screw. Because of the high-NA setup, the first screw threads are visible. (d, e) By shifting the lateral position of the virtual aperture, a sideways observation direction for the hypercentric imaging is selected. The insert shows an image of the laterally shifted aperture with d = 1.5 mm.
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