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Rakich A.,Binocular
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The Optical Plate Diagram of C. R. Burch has been generalized to allow the calculation of third-order perturbation aberrations for nominally axially symmetrical optical systems. The plate method has the advantage of simplifying the third-order analysis of optical systems by removing the first-order considerations that complicate traditional approaches. This development is shown to be directly analogous to the original derivation of Shack and Thompson. © 2010 Copyright SPIE - The International Society for Optical Engineering. Source

Schmid T.,University of Central Florida | Rolland J.P.,University of Central Florida | Rolland J.P.,University of Rochester | Rakich A.,Binocular | Thompson K.P.,Optical Research Associates
Optics Express | Year: 2010

We present the nodal aberration field response of Ritchey-Chrétien telescopes to a combination of optical component misalignments and astigmatic figure error on the primary mirror. It is shown that both astigmatic figure error and secondary mirror misalignments lead to binodal astigmatism, but that each type has unique, characteristic locations for the astigmatic nodes. Specifically, the characteristic node locations in the presence of astigmatic figure error (at the pupil) in an otherwise aligned telescope exhibit symmetry with respect to the field center, i.e. the midpoint between the astigmatic nodes remains at the field center. For the case of secondary mirror misalignments, one of the astigmatic nodes remains nearly at the field center (in a coma compensated state) as presented in Optics Express 18, 5282-5288 (2010), while the second astigmatic node moves away from the field center. This distinction leads directly to alignment methods that preserve the dynamic range of the active wavefront compensation component. © 2010 Optical Society of America. Source

Rakich A.,Binocular | Rakich A.,European Southern Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The Large Binocular Telescope (LBT) currently achieves collimation using a combination of collimation models and closed-loop active correction schemes. Shack Hartmann wavefront sensors with off-axis guide stars are used for Gregorian modes, and a closed-loop correction scheme is used for the prime-focus cameras. While in general this combination serves to produce alignment residuals well below a good seeing limit within a few minutes of obtaining a given target field, the uniquely asymmetrical structure of the LBT is prone to producing large deflections of the telescope optics when the ambient temperature is changing unusually rapidly. These deflections are difficult to model satisfactorily, and are an ongoing source of inefficiency in telescope operations. Furthermore, none of the current approaches to telescope collimation are particularly "piston aware"; a situation that needs to be improved on now that the LBT is commencing operations with the first of its beam combining instruments, LBTI. The laser tracker is a metrologyinstrument capable of automatically measuring optical element positions with better than 100 micron precision within a spherical volume of 30 m radius centered on the tracker head. With the ability to directly measure optics into position to this accuracy built into the Telescope Control System (TCS), the LBT would always be starting observations from a point of near-collimation, the component telescopes would be co-pointed, and the OPD would be well within the capture range of the beam combining instrument's internal phasing systems. This paper describes first results from engineering investigations into using the laser tracker to automatically align the optics on the LBT. © 2012 SPIE. Source

Rakich A.,Binocular
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The laser tracker allows the precise determination of positions of surfaces in three dimensions over volumes exceeding 30 m radius from the tracker head. At the Large Binocular Telescope a laser tracker has recently been employed for the initial alignment of all telescope optics in the right hand side (DX) bent Gregorian optical train. In this paper the particular approach to alignment of optical elements employed during this campaign is discussed in detail, together with results and expected accuracies. Subsequent to this "mechanical alignment" the telescope was taken "on-sky" and a subsequent "optical alignment" using a Shack-Hartman wavefront sensor with stellar sources took place. Ongoing activities include using the laser tracker to measure elevation and thermally induced displacements of individual optical elements. © 2010 SPIE. Source

Kapoula Z.,Binocular | Lang A.,Binocular | Vernet M.,Binocular | Locher P.,Montclair State University
Frontiers in Human Neuroscience | Year: 2015

Op Art generates illusory visual motion. It has been proposed that eye movements participate in such illusion. This study examined the effect of eye movement instructions (fixation vs. free exploration) on the sensation of motion as well as the body sway of subjects viewing Op Art paintings. Twenty-eight healthy adults in orthostatic stance were successively exposed to three visual stimuli consisting of one figure representing a cross (baseline condition) and two Op Art paintings providing sense of motion in depth–Bridget Riley’s Movements in Squares and Akiyoshi Kitaoka’s Rollers. Before their exposure to the Op Art images, participants were instructed either to fixate at the center of the image (fixation condition) or to explore the artwork (free viewing condition). Posture was measured for 30 s per condition using a body fixed sensor (accelerometer). The major finding of this study is that the two Op Art paintings induced a larger anteroposterior body sway both in terms of speed and displacement and an increased motion illusion in the free viewing condition as compared to the fixation condition. For body sway, this effect was significant for the Riley painting, while for motion illusion this effect was significant for Kitaoka’s image. These results are attributed to macro-saccades presumably occurring under free viewing instructions, and most likely to the small vergence drifts during fixations following the saccades; such movements in interaction with visual properties of each image would increase either the illusory motion sensation or the antero-posterior body sway. © 2015 2015Soh,Skocic,Nash,Stevens,TurnerandRovet. Source

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