Tilt Lens Research Articles

In situ size and motility measurement of aquatic invertebrates with an underwater stereoscopic camera system using tilted lenses

Abstract In situ observation of traits of aquatic organisms, including size and motility, requires three‐dimensional measurements that are commonly done with a stereoscopic imaging system. However, to observe traits of small aquatic invertebrates, the imaging system requires relatively high magnification, which results in a small overlapping volume between the two cameras of a conventional stereoscopic system. The provision of a larger shared volume would therefore be of great advantage, especially, when the organism abundance is low. We implement a stereoscopic system that utilizes a tilted lens approach, known as the Scheimpflug principle, to increase the common imaging volume of two cameras. The system was calibrated and tested in the laboratory and then deployed in a saltmarsh to observe water boatmen Trichocorixa californica. Processing of the image data from the field deployments resulted in the simultaneous estimation of the traits of body length and swimming speed of the aquatic insects. Our stereo setup with tilted lenses increased the sampling volume by 3.1 times compared to a traditional stereo setup with the same optical parameters. The in situ data and subsequent processing reveal that the instrument can capture stereoscopic images that resolve both body length and swimming speed of the aquatic insects. Results indicate that the relationship between the body length and the swimming speed of the water boatmen is linear in the log–log space with an exponent of . Furthermore, the insects experience Reynold's number in the range of –. Our results demonstrated that the system can be used to observe key traits of small aquatic organisms in an ecologically relevant context. This work expands the capability of underwater imaging systems to measure important traits of an individual aquatic invertebrate in its natural environment and aids in providing a trait‐based approach to zooplankton ecology.

A Comprehensive and Versatile Camera Model for Cameras with Tilt Lenses

We propose camera models for cameras that are equipped with lenses that can be tilted in an arbitrary direction (often called Scheimpflug optics). The proposed models are comprehensive: they can handle all tilt lens types that are in common use for machine vision and consumer cameras and correctly describe the imaging geometry of lenses for which the ray angles in object and image space differ, which is true for many lenses. Furthermore, they are versatile since they can also be used to describe the rectification geometry of a stereo image pair in which one camera is perspective and the other camera is telecentric. We also examine the degeneracies of the models and propose methods to handle the degeneracies. Furthermore, we examine the relation of the proposed camera models to different classes of projective camera matrices and show that all classes of projective cameras can be interpreted as cameras with tilt lenses in a natural manner. In addition, we propose an algorithm that can calibrate an arbitrary combination of perspective and telecentric cameras (no matter whether they are tilted or untilted). The calibration algorithm uses a planar calibration object with circular control points. It is well known that circular control points may lead to biased calibration results. We propose two efficient algorithms to remove the bias and thus obtain accurate calibration results. Finally, we perform an extensive evaluation of the proposed camera models and calibration algorithms that establishes the validity and accuracy of the proposed models.

Removal of ghost images by using tilted element optical systems with polynomial surfaces for aberration compensation

A novel solution to problematic ghost images is implemented by using tilted lens elements with polynomial surfaces. Tilting the lens surfaces sends reflections out of the imaging path. The nonrotationally symmetric polynomial surfaces correct aberrations caused by tilts. The complex lens surfaces are fabricated by using gray-scale lithographic patterning of hybrid solgel glass.

Simulation of A Wedge Plate Interferometer Using Holo Optical Elements

A wedge plate interferometer has been constructed using holo optical elements (HOEs). It comprises of two HOEs namely a Holo Shear Lens (HSL) and a Holo Shear Tilt Lens (HSTL). The combined effect of the two is to introduce a lateral shear and a tilt between the sheared wavefronts, the tilt beign orthogonal to the shear direction. This is equivalent to the conventional shear itnerferometer using a wedge plate for collimation testing. Theory and experimental results are presented.

Gravity Survey and Geological Interpretation, Northern New York1

About 2000 gravity stations were established 3-5 miles apart in the Adirondack Mountains and surrounding area. The data show an excellent correlation with geology: the anorthosite bodies are conspicuously outlined by gravity lows; the Northwest Adirondacks, a belt of Grenville rocks along the St. Lawrence River, is associated with a gravity high; and centered over Tug Hill is a small gravity low. A few of the 23 residual anomalies in the area have no apparent correlation with geology. The residual anomaly limits the possible three dimensional shapes of the anorthosite massif; it cannot be a batholith or a large tilted lens. It is essentially a slab having two roots that extend downward about 10 km. Because the residual anomaly is a gravity low, the anorthosite is less dense than the surrounding rocks. The density of the anorthosite is 2.72 gm/cm 3 , and the density contrast is −0.10, implying that the average density of the surrounding Precambrian rocks is 2.82. Variations in the regional anomaly are attributable to small warps of the M discontinuity. A north-trending ridge with 2 degree dip 36 km beneath the mountains satisfies the gravity data and conforms with previous seismic work. The regional isostatic anomaly, near zero in the immediate vicinity of the mountains, suggests that the region is near isostatic balance.