The receptive fields of Daphnia ommatidia

1976 ◽  
Vol 64 (1) ◽  
pp. 185-202
Author(s):  
S. Young ◽  
A. C. Downing
Keyword(s):  
Refractive Index ◽  
Direct Observation ◽  
Focal Length ◽  
Receptive Fields ◽  
Ray Optics

1. The focal length and positions of the principal planes of an isolated Daphnia lens were determined, and the refractive index of the rhabdom was measured. 2. The lens can form an image, but this always lies well behind the rhabdom. This was confirmed by direct observation of images inside a clear-eye mutant Daphnia eye. 3. The rhabdom was shown to be unlikely to function as a waveguide, and a ray optics model is proposed to enable the prediction of ommatidial receptive fields from the lens data. 4. The predicted receptive fields have wide plateaus and steep sides, and there are virtually no totally blind gaps between neighbouring ommatidia.

scholarly journals The scattering of light by turbid media.–Part II

1931 ◽  
Vol 131 (817) ◽  
pp. 464-475 ◽  
Keyword(s):  
Refractive Index ◽  
Absorption Coefficient ◽  
Spherical Shell ◽  
Direct Observation ◽  
Single Particle ◽  
Unit Volume ◽  
Incident Light ◽  
Parallel Beam ◽  
Photometric Observations ◽  
Transmission And Reflection

In Part I it was shown how the values of the transmission and reflection of a sheet of a medium containing particles in suspension can he calculated. First the amounts of light scattered in the forward and forward directions from a single particle were determined; from these results the transmission 1 and rejection R for diffuse incident light were found for a layer of the disusing medium, when the effects of boundary reflections are negligible. At this stage, the expressions developed apply to a mist or fog consisting of particles suspended in air. Finally it was shown how, if the particles are suspended in some other medium, having a different refractive index from that of air, the transmission and reflection ז and p can be expressed in terms of T and R and the surface rejection coefficients. The more general expressions, for the case when the incident light is a parallel beam, were also developed. We shall now show how the absorption coefficient μ can be determined from photometric observations. As a check on the theory, we shall deduce the diameter D of the particles and the number N present per unit volume and compare these calculated values with those found by direct observation, Finally, the necessary modifications of the theory will be made to cover the case when the diffusing medium is in the form of a spherical shell.

scholarly journals Resolution and Sensitivity in the Eye of the Winkle Littorina Littorea

1992 ◽  
Vol 170 (1) ◽  
pp. 57-69
Author(s):  
JAN-OLOF SEYER
Keyword(s):  
Electron Microscopy ◽  
Refractive Index ◽  
Focal Length ◽  
Light And Electron Microscopy ◽  
Geometrical Model ◽  
Radius Ratio ◽  
Visual Performance ◽  
Littorina Littorea ◽  
Marine Animals ◽  
Lens Radius

The winkle Littorina littorea (L.) has camera-type (simple) eyes. Light and electron microscopy were used to generate an accurate geometrical model of the eye, and this was used to predict the eye's visual performance. The lens is spherical with a diameter of 112 μm, and examination of images formed by isolated lenses indicates a mean focal length in water of 126 μm. These images are crisp and apparently aberration-free. This, in addition to a shorter than expected focal length, implicates the presence of a gradient of refractive index in the lens. The lens has a focal length to lens-radius ratio of 2.3, which is close to the ‘Matthiessen ratio’ of 2.5 found in the aplanatic lenses of many other marine animals. The lens is predicted to focus images within the retina only when the eye is submerged in water: in air, images are focused distal to the retina. In the central retina, the inter-receptor angle is 1.8° and the rhabdom diameter is 4 μm (5.5 times larger than the diffraction blur-circle), indicating a retinal array coarser than that necessary to sample all the information contained in the image. In addition, a low F-number (1.2) and the large possible angles of incidence of rays striking the retina (up to 40°) mean that the eye is likely to suffer substantial spreading of light between rhabdoms (which are unshielded) and further degradation of resolution. Possible behavioural roles for the eyes are discussed.

scholarly journals Electrically-Tunable Blue Phase Liquid Crystal Microlens Array Based on a Photoconductive Film

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 65 ◽  
Author(s):  
Bing-Yau Huang ◽  
Shuan-Yu Huang ◽  
Chia-Hsien Chuang ◽  
Chie-Tong Kuo
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Electric Field ◽  
Uv Light ◽  
Focal Length ◽  
Incident Light ◽  
Microlens Array ◽  
Gradient Distribution ◽  
Phase Liquid ◽  
Blue Phase

This paper proposes an effective approach to fabricate a blue phase liquid crystal (BPLC) microlens array based on a photoconductive film. Owing to the characteristics of photo-induced conducting polymer polyvinylcarbazole (PVK), in which conductivity depends on the irradiation of UV light, a progressive mask resulting in the variation of conductivity is adopted to produce the gradient distribution of the electric field. The reorientations of liquid crystals according to the gradient distribution of the electric field induce the variation of the refractive index. Thus, the incident light experiences the gradient distribution of the refractive index and results in the focusing phenomenon. The study investigates the dependence of lens performance on UV exposure time, the focal length of the lens, and focusing intensities with various incident polarizations. The BPLC microlens array exhibits advantages such as electrically tunability, polarization independence, and fast response time.

scholarly journals CAMERA CONSTANT IN THE CASE OF TWO MEDIA PHOTOGRAMMETRY

2015 ◽  
Vol XL-5/W5 ◽  
pp. 1-6 ◽  
Author(s):  
P. Agrafiotis ◽  
A. Georgopoulos
Keyword(s):  
Refractive Index ◽  
Camera Calibration ◽  
Focal Length ◽  
Calibration Procedure ◽  
Water Salinity ◽  
Clean Water ◽  
Object Distance ◽  
Calibration Methods ◽  
The One ◽  
Probable Relation

Refraction is the main cause of geometric distortions in the case of two media photogrammetry. However, this effect cannot be compensated and corrected by a suitable camera calibration procedure (Georgopoulos and Agrafiotis, 2012). In addition, according to the literature (Lavest et al. 2000), when the camera is underwater, the effective focal length is approximately equal to that in the air multiplied by the refractive index of water. This ratio depends on the composition of the water (salinity, temperature, etc.) and usually ranges from 1.10 to 1.34. It seems, that in two media photogrammetry, the 1.33 factor used for clean water in underwater cases does not apply and the most probable relation of the effective camera constant to the one in air is depending of the percentages of air and water within the total camera-to-object distance. This paper examines this relation in detail, verifies it and develops it through the application of calibration methods using different test fields. In addition the current methodologies for underwater and two-media calibration are mentioned and the problem of two-media calibration is described and analysed.

scholarly journals Electrostrictive Mechanism of Radiation Self-Action in Nanofluids

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Albert Livashvili ◽  
Victor Krishtop ◽  
Margarita Yakunina
Keyword(s):  
Refractive Index ◽  
Analytical Solution ◽  
Diffusion Equation ◽  
Radiation Intensity ◽  
Focal Length ◽  
Hydrodynamic Characteristics ◽  
Nonlinear Part ◽  
Self Focusing ◽  
Lens Focal Length ◽  
Dynamics Of Particles

The electrostriction mechanism of beam self-focusing in nanofluids is theoretically investigated. An analytical solution of the diffusion equation, which describes the dynamics of particles in nanofluids, was obtained and studied. Explicit expressions for the nonlinear part of the refractive index and concentration lens focal length are presented. It is shown that there is a limit on the radiation intensity associated with the physical and hydrodynamic characteristics of the phenomena in these processes.

scholarly journals Experiments relative to the effect of temperature on the refractive index and dispersive power of expansible fluids, and on the influence of these changes in a telescope with a fluid lens

1833 ◽  
Vol 2 ◽  
pp. 345-346
Keyword(s):  
Refractive Index ◽  
Focal Length ◽  
Effect Of Temperature ◽  
Focal Power ◽  
Dispersive Power

In a paper lately read to the Society, the author stated that he had not perceived any change in the focal length of the telescope, induced by changes of temperature; but he has since ascertained that in order to produce the brightest and most perfect image, the distance of the object-glass requires a minute adjustment, amounting to 0·134 of an inch, corresponding to an elevation of temperature from 57° to 84°, or a depression from 57° to 31°. In order to introduce greater clearness and precision, the author proceeds to define certain terms which he finds it necessary to employ. By the length of the telescope , he would be understood to mean the distance between the object-glass and the focus; by the fluid focus , that between the fluid lens and the focus; and by the focal power of the telescope, he means the focal length of a telescope of the usual construction, which gives the same convergency to the rays, or produces an image of the same size: but he also employs the term focal length of the telescope , as synonymous with the first; that of fluid focal length as synonymous with the second; and that of equivalent focal length as synonymous with the last of these terms.

Non-Destructive Measurement of Doublet Objective Lens Structure Parameters Based on ZEMAX

2014 ◽  
Vol 635-637 ◽  
pp. 694-697
Author(s):  
Xin Bian ◽  
Feng Huang ◽  
Guo Rong Cao ◽  
Zheng Ling Wang
Keyword(s):  
Refractive Index ◽  
Focal Length ◽  
Optimal Combination ◽  
Radius Of Curvature ◽  
Objective Lens ◽  
Structure Parameters ◽  
Evaluation Function ◽  
Destructive Measurement ◽  
Non Destructive ◽  
Back Focal Length

A method for structure parameters of doublet objective lens with non-destructive measurement is proposed based on the ZEMAX software. The focal length, back focal length, central thickness and the radius of curvature of the first surface and last surface are measured by a spherical interferometer and other instruments. Using the inversion of the evaluation function and optimizing of the ZEMAX, the series of refractive index of the materials and the cemented surface of the doublet objective lens are derived. Then the optimal combination of the glass materials is selected by the aberration tolerances of the doublet objective lens. The examples show that the result is satisfactory.

scholarly journals Liquid Crystal Microlens Using Nanoparticle-Induced Vertical Alignment

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Shug-June Hwang ◽  
Yi-Ming Shieh ◽  
Kuo-Ren Lin
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Focal Length ◽  
Nonuniform Distribution ◽  
Vertical Alignment ◽  
Alignment Layer ◽  
Focus Effect ◽  
Oligomeric Silsesquioxane ◽  
Poss Nanoparticle

The nanoparticle-induced vertical alignment (NIVA) of the nematic liquid crystals (LC) is applied to achieve an adaptive flat LC microlens with hybrid-aligned nematic (HAN) mode by dropping polyhedral oligomeric silsesquioxane (POSS) nanoparticle solution on a homogeneous alignment layer. The vertical alignment induced by the POSS nanoparticles resulted in the formation of a hybrid-aligned LC layer with concentric nonuniform distribution of the refractive index in the planar LC cell, which subsequently played the role of the lens, even in the absence of any applied voltages. The dimensions of the concentric HAN structure significantly depend on the volume of the microdroplet and the POSS concentration. The focus effect of this flat microlens was observed while electrically controlling its focal length using the applied voltages from −50 mm to −90 mm.

scholarly journals LENS QUASI-OPTICAL TRANSMISSION LINE WITH OPTICAL CONTRAST CLOSE TO 1

2019 ◽  
Vol 8 ◽  
pp. 93-99
Author(s):  
Oleg Minin ◽  
Igor Minin
Keyword(s):  
Refractive Index ◽  
Laser Radiation ◽  
Transmission Line ◽  
Optical Transmission ◽  
Optical Axis ◽  
Focal Length ◽  
Optical Contrast ◽  
Biological Media ◽  
X Ray

The quasi-optical transmission line with optical contrast close to 1 is considered. Such devices can be used to study the effect of laser radiation on biological media, in microwave, terahertz, optical and X-ray wavelength ranges, as well as in acoustics. The use of composite refractive lenses, which are a set of identical spherical lenses arranged one after another on the same optical axis and with a refractive index close to one, reduces the loss of reflection in such a lens. Reducing the focal length in such refractive lenses is possible by increasing the number of refractive surfaces.

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