VOB Virtual Optical Bench Program Series
Fig. 6-1 shows a system with a double lens (f =94 mm). The aperture stop (30 mm) is located at the lens. Object width and image width are both 2 * 94 mm, resulting in an 1 : 1 projection.
Fig. 6-1: Simple system with double lens
Fig. 6-2 shows a the same system converted to a basic telecentric system as it is used in metrology. The aperture stop (3 mm) is now located at the focus F` (94 mm), being the exit pupil. The entrance pupil is in infinity (to the left). Principal rays are parallel to the optical axis at the object and go through the focus. A displacement of the object does (more or less) not affect the image height of the projection on the screen (most right), magnification is constant. The object heights are 0, 5, and 10 mm for the yellow, green and red ray bundles, respectively.
Fig. 6-2: Telecentric system with aperture stop of 1 mm
Constant magnification with changing object distance is demonstrated by animation of object distance (Fig 6-3). The object width varies between 300 and 20 mm in step of 10 mm. By VOB++ an animation sequence was produced and recorded as avi file. In order to minimize file size the avi file was converted to an animated gif.
Fig. 6-3: Animated telecentric system with aperture stop of 1 mm
Fig. 6-2 shows a record of the corresponding spot size for three object heights. Note the increasing chromatic aberration (false colors) with increasing object height.
Fig. 6-4: Variation of spot sizes for telecentric system with aperture stop of 1 mm
Fig. 6-5 and 6-6 show results for aperture stop of 3 mm. For more information about telecentric systems see
Gottfried Schröder, Technische Optik, 1990, Vogel Buchverlag, Würzburg
Warren J. Smith, Modern Optical Engineering, 2nd Ed., McGraw-Hill, NY
Fig. 6-5: Animated telecentric system with aperture stop of 3 mm
Fig. 6-6: Variation of spot sizes for telecentric system with aperture stop of 3 mm
Webmaster`s note: Soon (ehem, in the next weeks ;-) we will add synthesized images for this telecentric system. Suggestions for example systems are welcomed. Please come in again.
