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incorrect positioning of the film in the camera, physical distortion of the film media in the development process, and (if digitally scanned) the nonlinearity of the image scanner. These errors may be visually imperceptible but limit the precision of measurements. Because the position of the marks is very precisely known, the image can easily be corrected to account for these effects. When used for
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the fiducial markers will be evenly spaced on the positive image. Uneven spacing reveals that the image has been distorted. Identical spacing on adjacent images (e.g. from a series of aerial photos) ensures that printing magnification is consistent. Irregularities in the grid can also result from
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The Réseau plate was engraved with a 5 × 5 grid of crosses. The intersections of the crosses were 10 mm apart and accurately calibrated to a tolerance of 0.002 mm. Except for the double-sized central cross, each of the four arms on a cross was 1 mm long and 0.02 mm wide. The
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When the
Hasselblad lunar surface data camera was fitted with a 60 mm lens, the images of the Réseau crosses on the film have an apparent separation of 10.3 degrees. With a 500 mm lens fitted, the apparent separation is 1.24 degrees.
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was fitted with a Réseau plate made of glass and fitted to the back of the camera body, extremely close to the film plane. The plate was 5.4 × 5.4 cm in the film plane, which was the useful exposure area on the 70 mm film.
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Fiducial markers are generally unnecessary for digital cameras because the physical pixel structure of the sensor itself inherently provides a source of geometric reference.
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of the camera just in front of the film. When the frame is exposed the fiducial markers scatter incoming light, creating a permanent shadow on the negative.
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The fiducial markers on a Réseau plate are sometimes called reticles. The Latin root of fiducial means
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An accidental exposure from the
Hasselblad lunar surface data camera showing the Réseau crosses.
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is a transparent sheet of glass or plastic engraved with a grid of crosshatches called
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54:; fiducial markers are trustworthy reference points. The Latin root of reticle means
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Transparent camera lens attachment used to aid in scientific measurements
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43:) for scientific and technical photography. The plate is placed at the
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Markus
Mehring; Phill Parker; David Woods & Eric Jones.
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129:"The Réseau Measurement in ELCOVISION 10"
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107:between objects in the field-of-view.
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88:Hasselblad lunar surface data camera
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66:If the film negative is properly
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56:small meshwork bag, small net
162:Apollo Lunar Surface Journal
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35:. It was commonly used in
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182:Photography equipment
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145:. Moon Base Clavius.
92:Apollo Moon missions
82:Use on lunar cameras
62:Purpose and function
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105:angular distances
52:trust, confidence
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158:"Réseau Plate"
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37:film cameras
29:Réseau plate
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45:focal plane
176:Categories
115:References
101:fiducials
164:. NASA.
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