Anatomy of the Regional Differences in the Eye of the Mantis Ciulfina

1979 ◽  
Vol 80 (1) ◽  
pp. 165-190 ◽  
Author(s):  
G. A. HORRIDGE ◽  
PETER DUELLI
Keyword(s):  
Regional Differences ◽  
Compound Eye ◽  
Focal Length ◽  
Visual Fields ◽  
Resolving Power ◽  
Acceptance Angle ◽  
Extended Source ◽  
Angular Coordinates ◽  
The Individual ◽  
Different Parts

In the compound eye of Ciulfina (Mantidae) there are large regional differences in interommatidial angle as measured optically from the pseudopupil. Notably there is an acute zone which looks backwards as well as one looking forwards. There are correlated regional differences in the dimensions of the ommatidia. The following anatomical features which influence the optical performance have been measured in different parts of the eye The facet diameter is greater where the interommatidial angle is smaller. This could influence resolving power, but calculation shows that facet size does not exert a dominant effect on the visual fields of the receptors. The rhabdom tip diameter, which theoretically has a strong influence on the size of visual fields, is narrower in eye regions where the interommatidial angle is smaller. The cone length, from which the focal length can be estimated, is greater where the interommatidial angle is smaller. Estimation of the amount of light reaching the rhabdom suggests that different parts of the eye have similar sensitivity to a point source of light, but differ by a factor of at least 10 in sensitivity to an extended source. There is anatomical evidence that in the acute zone the sensitivity has been sacrificed for the sake of resolution. Maps of the theoretical minimum fields of the photoreceptors, plotted in their positions on the eye in angular coordinates, suggest that there are too few ommatidia for the eye as a whole to reconstruct all the visual detail that the individual receptors can resolve. The conclusion from (3) and (4), together with some behavioural evidence, suggests that the eye structure must make possible the resolution of small movements of contrasting edges and of small dark contrasting objects but there is less emphasis on the total reconstruction of fine patterns because the interommatidial angle is greater than the estimate of the acceptance angle.

Review lecture: Apposition eyes of large diurnal insects as organs adapted to seeing

1980 ◽  
Vol 207 (1168) ◽  
pp. 287-309 ◽  
Keyword(s):  
Nodal Point ◽  
Visual Fields ◽  
Photoreceptor Cells ◽  
Resolving Power ◽  
Field Size ◽  
Correct Position ◽  
Anatomical Arrangement ◽  
Angular Coordinates ◽  
And Function ◽  
Facet Size

(1) The fields of view of the photoreceptor cells are determined by the dimensions and anatomical arrangement of the optical part of the ommatidium. The dimensions, and therefore the fields of view of the ommatidia are also related across the eye. In the relation between structure and function there are many points that invite discussion, but the intention is to order our knowledge so that the gaps become obvious. (2) The first step has been to make maps of the eyes showing the maximum theoretical resolving power of the facets and also the interommatidial angle, the reciprocal of which is the maximum spatial resolution of combinations of facets. The ratio of these two resolutions at each point shows the minimum overlap of the visual fields. These maps can be made from the outside of the eye; they show the main types of eye. (3) The next step is to work out the optics of individual ommatidia so that the focal lengths and receptor widths can be measured. The field width can then be predicted from the facet size and the subtense of the receptor at the posterior nodal point. The final step is to measure the field widths of individual ommatidia experimentally as a test of the optical theory, and to make maps of the actual fields in their correct position on the eye in angular coordinates. (4) Three examples of maps of actual fields are given, and their anato­mical and diffraction components are separated. The maps are an essential step towards the electrophysiological analysis of the ganglia behind the eye. A theory of the origin of the fields in terms of anatomy and optics also opens the way to an analysis of mechanisms that change the field size upon adaptation to light. A comparative study of the fields in different eye regions and in different species can also be related to visual habits and behaviour.

scholarly journals X-ray picture of the Sun taken with Fresnel zone plates

1968 ◽  
Vol 35 ◽  
pp. 439-443
Author(s):  
G. Elwert
Keyword(s):  
Fresnel Zone ◽  
Focal Length ◽  
Brightness Distribution ◽  
Resolving Power ◽  
X Rays ◽  
Applied Physics ◽  
Fresnel Zone Plates ◽  
Zone Plates ◽  
The One ◽  
The Individual

It is well known that Fresnel zone plates act as a lens with a focal length inversely proportional to the wavelength. At Professor Moellenstedt's Institute of Applied Physics in Tübingen, a technique has been developed to manufacture micro-zone plates electronoptically from Buckbee-Mears zone plates. These micro-zone plates have a diameter of 0·5 mm approximately, 38 zones and a focal length of 30 cm for X-rays of nearly 50 Å. Their resolving power is of the order of a few seconds of arc (Einighammer et al., 1966). One finds, however, experimentally as well as theoretically that the sharply defined image is surrounded by a halo having a diameter of a few minutes of arc for the above-mentioned zone plates. Whereas for a point source the intensity of a halo is poor and therefore unimportant, for extended sources it becomes large as a result of the superposition of the contributions from the individual points of the source. This has been demonstrated by the photometer curves of the images of circular sources by Einighammer (1966) (Figure 1). The halo is not noticeable in case of very narrow sources (curves a and b). With increasing diameter of the source the intensity of the halo rapidly increases (curves c and d). For the same source the brightness distribution of the halo agrees practically with the one obtained by a pinhole camera, provided the diameter of the hole and that of the zone plate are equal; these brightness distributions are represented by the dashed lines c′ d′ in Figure 1.

Regionally different optical systems in the compound eye of the water-flea Polyphemus (Cladocera, Crustacea)

1983 ◽  
Vol 217 (1207) ◽  
pp. 163-175 ◽  
Keyword(s):  
Regional Differences ◽  
Compound Eye ◽  
Focal Length ◽  
Complex Refractive Index ◽  
Optical Design ◽  
Optical Systems ◽  
Refractive Index Gradient ◽  
Water Flea ◽  
Central Type ◽  
Index Gradient

Polyphemus pediculus (L.) is a small (1 mm long) predatory crustacean that lives in bodies of standing freshwater. It has a single fused compound eye, which occupies most of its head. The eye comprises 130 ommatidia with five distinct types of crystalline cones. Four of these cone types were found to focus light by means of gradient index optics (lens cylinders). The edge ommatidia differ by having the focus displaced below the distal rhabdom tip. This was found to be correlated with their special type of rhabdom, which is characterized by its short, broad shape and the absence of a palisade. The central-type crystalline cone, contributing to a zone of acute vision, is functionally different from the other four cone types. The focusing on the rhabdom tip is in this case achieved by a prism, inside the cone, corrected for optical aberration with a complex refractive index gradient. The prism is interpreted as a way of compressing a long focal length into a short optical system, i. e. to enable high resolution in spite of the small size of the eye. Extreme regional differences in interommatidial angles were found to be the main reason for the different optical design between central and peripheral ommatidia.

The eye of Anoplognathus (Coleoptera, Scarabaeidae)

1975 ◽  
Vol 188 (1090) ◽  
pp. 1-30 ◽  
Keyword(s):  
Refractive Index ◽  
Point Source ◽  
Dark Adaptation ◽  
Compound Eye ◽  
Visual Fields ◽  
Optomotor Response ◽  
Clear Zone ◽  
Acceptance Angle ◽  
Single Plane ◽  
Receptor Layer

The night flying scarabaeid beetle Anoplognathus provides an example of a dark-adapted clear-zone compound eye in which rays from a distant point source, entering by a large patch of facets, are imperfectly focused upon the receptor layer. The optical system of the eye was investigated by six methods, all of which give similar results: (1) ray tracing through structures of known refractive index, (2) measurement of visual fields of single receptors, (3) measurement of the divergence of eyeshine, and (4) of the optomotor response to stripes of decreasing width, and (5) by direct observation of distribution of light within the eye. Finally (6) anatomically there is no single plane upon which an image could be focused. In each ommatidium, beneath the thick cornea, with its short corneal cone, lies a non-homogeneous crystalline cone (range of r. i. 1.442-1.365) that is significant in partially focusing rays across the wide clear zone (340 μm) in the dark-adapted eye. On the proximal side of the clear zone the rhabdoms form 7-lobed columns, isolated from each other over half their length by a tracheal tapetum. In the light-adapted eye the cone cells extend to form a crystalline tract (70-90 μm long) which is sur­rounded by dense pigment, and the optical path across the clear zone is completed by retinula cell columns that are of higher density than the surrounding cells. Pigment movement upon adaptation takes about 10 min to complete. Dark adaptation can be induced only at night on account of a strong diurnal rhythm. Eyeshine can be seen in the dark-adapted eye so long as the distal pig­ment leaves free the tips of the crystalline cones. Eyeshine falls to 50% at an angle of 12° from the direction of a parallel beam shining on the eye, as is consistent with a partial focus in which the distribution of light on the receptor layer is 18°-24° wide at the 50% contour. This distribution was confirmed by direct examination of the inside of the eye and by measure­ment of receptor fields as follows. The mean acceptance angle for 13 light-adapted units was 12.57° ± 1.97° s. d. and that of 10 dark-adapted ones 20.3° ± 3.36° s. d. The sensi­tivity to a point source on axis is increased at least 1000 fold by dark adaptation. Rays traced through a scale drawing of the eye, with refractive index measured for each component, show how the eye as a whole comes to be partially focused, and predicts an acceptance angle of 12° in the light-adapted and 20°-24° in the dark-adapted eye. In optomotor experiments dark-adapted Anoplognathus does not respond to stripes narrower than 18° repeat period, but light-adapted beetles respond down to 10°. The optomotor experiments also show a 1000 fold increase in sensitivity when dark-adapted at night. The eye has poor acuity that goes with wide visual fields of its recep­tors, and this is surprising when other excellently focused clear zone eyes are known. A possible compensation for the poor acuity is that the aperture of the eye can be larger, so that sensitivity although only to large objects, is that much increased.

scholarly journals TYPOLOGY OF PERIPHERAL VISION

2020 ◽  
Author(s):  
Yevgeny Soenko ◽  
Keyword(s):  
Visual System ◽  
Electrical Activity ◽  
Peripheral Vision ◽  
Visual Fields ◽  
Individual Case ◽  
Physiological Changes ◽  
General Acceptance ◽  
The Individual ◽  
Stable Preference ◽  
Different Parts

The research is based on the statement that retina produces the proper level of electrical activity, sourcing visual system. I started the research with partial darkening of different parts of the visual fields of humans to register possible psychological and physiological changes. The tested showed dramatically increasing variability and number of changes within just four exact types of darkening. More, emotional and physiological aspects of those changes were polarized into general acceptance and general rejection of a certain type of darkening in most of the individual tests. Thus the tested formed two opposite groups within every one of those types of darkening: a group with general negative reactions and a group with general positive ones. Further, those types of darkening turned out combined in pairs. General tune of reactions of most of the tested changed to strictly reverse within a pair of upper-lower types of darkening of peripheral vision and outer-inner ones as well. Between the pairs of types of darkening, there was no correspondence. The tested showed stability of their reactions during at least several months. Thus I may state a possibility of existence in the visual system of humans of two independent neuropsychological structures both having two alternative modes of functioning with a stable preference of just one of them in every individual case. If it is true, there may be a vision-based typology.

Study on Pramana Shareera in relation to Prakriti

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Rajendra Pai N. ◽  
U. Govindaraju
Keyword(s):  
Observational Study ◽  
Upper Limb ◽  
Lower Limb ◽  
Characteristic Property ◽  
The Body ◽  
Artificial Limbs ◽  
Body Parts ◽  
Unit Of Measurement ◽  
The Individual ◽  
Different Parts

Ayurveda in its principle has given importance to individualistic approach rather than generalize. Application of this examination can be clearly seem like even though two patients suffering from same disease, the treatment modality may change depending upon the results of Dashvidha Pariksha. Prakruti and Pramana both used in Dashvidha Pariksha. Both determine the health of the individual and Bala (strength) of Rogi (Patient). Ayurveda followed Swa-angula Pramana as the unit of measurement for measuring the different parts of the body which is prime step assessing patient before treatment. Sushruta and Charaka had stated different Angula Pramana of each Pratyanga (body parts). Specificity is the characteristic property of Swa-angula Pramana. This can be applicable in present era for example artificial limbs. A scientific research includes collection, compilation, analysis and lastly scrutiny of entire findings to arrive at a conclusion. Study of Pramana and its relation with Prakruti was conducted in 1000 volunteers using Prakruti Parkishan proforma with an objective of evaluation of Anguli Pramana in various Prakriti. It was observed co-relating Pramana in each Prakruti and Granthokta Pramana that there is no vast difference in measurement of head, upper limb and lower limb. The observational study shows closer relation of features with classical texts.

scholarly journals Monte Carlo Ray-Tracing Simulation of a Cassegrain Solar Concentrator Module for CPV

2021 ◽  
Vol 9 ◽  
Author(s):  
Seung Jin Oh ◽  
Hyungchan Kim ◽  
Youngsun Hong
Keyword(s):  
Monte Carlo ◽  
Ray Tracing ◽  
Concentration Ratio ◽  
Collection Efficiency ◽  
Focal Length ◽  
Tracking Error ◽  
Target Area ◽  
Solar Concentrator ◽  
Acceptance Angle ◽  
Energy Applications

The concentration ratio is one of the most important characteristics in designing a Cassegrain solar concentrator since it directly affects the performance of high-density solar energy applications such as concentrated photovoltaics (CPVs). In this study, solar concentrator modules that have different configurations were proposed and their performances were compared by means of a Monte Carlo ray-tracing algorithm to identify the optimal configurations. The first solar concentrator design includes a primary parabolic concentrator, a parabolic secondary reflector, and a homogenizer. The second design, on the other hand, includes a parabolic primary concentrator, a secondary hyperbolic concentrator, and a homogenizer. Two different reflectance were applied to find the ideal concentration ratio and the actual concentration ratio. In addition, uniform rays and solar rays also were compared to estimate their efficiency. Results revealed that both modules show identical concentration ratios of 610 when the tracking error is not considered. However, the concentration ratio of the first design rapidly drops when the sun tracking error overshoots even 0.1°, whereas the concentration ratio of the second design remained constant within the range of the 0.8° tracking error. It was concluded that a paraboloidal reflector is not appropriate for the second mirror in a Cassegrain concentrator due to its low acceptance angle. The maximum collection efficiency was achieved when the f-number is smaller and the rim angle is bigger and when the secondary reflector is in a hyperboloid shape. The target area has to be rather bigger with a shorter focal length for the secondary reflector to obtain a wider acceptance angle.

Improved Alignment Technique for Dish Concentrators

Solar Energy ◽  
2003 ◽  
Author(s):  
Charles E. Andraka ◽  
Richard B. Diver ◽  
K. Scott Rawlinson
Keyword(s):  
Focal Length ◽  
Electric Energy ◽  
Parabolic Systems ◽  
Companion Paper ◽  
Quantitative Information ◽  
Key Factors ◽  
Look Back ◽  
Parabolic Dish ◽  
The Individual

Parabolic dish concentrators have shown significant promise of generating competitive electric energy for grid and off-grid applications. The efficiency of a dish-electric system is strongly affected by the quality of the concentrator optics. Most parabolic systems consist of a number of facets mounted to a support structure in an approximate parabolic arrangement, where the individual facets have spherical or parabolic optical shapes. The individual facets must be accurately aligned because improper alignment can compromise performance or create hot spots that can reduce receiver life. A number of techniques have been used over the years to align concentrator facets. In the Advanced Dish Development System (ADDS) project, a color look-back alignment approach that accurately aligns facets (mirror panels) and in addition indicates quantitative information about the focal length was developed. Key factors influencing the alignment, some of which had very large effects on the quality of the alignment, were also identified. The influence of some of the key factors was characterized with a flux mapping system on the second-generation ADDS concentrator. Some of these factors also affect other alignment approaches. The approach was also successfully applied to two other concentrators with differing facet arrangements. Finally, we have extended the method to a 2-f approach that eliminates the need for a distant line-of-sight to the dish and permits alignment at near vertical dish attitudes. In this paper, we outline the color look-back alignment approach, discuss the key alignment factors and their effect on flux distribution, and discuss extensions to non-gore dishes. A companion paper discusses the 2-f color alignment approach in detail.

Discrimination Between Movements of Eye and Object by Visual Interneurones of Crickets

1969 ◽  
Vol 50 (3) ◽  
pp. 723-732
Author(s):  
JOHN PALKA
Keyword(s):  
Eye Movement ◽  
Voluntary Movement ◽  
Compound Eye ◽  
Visual Fields ◽  
Object Motion ◽  
Visual Environment ◽  
Inhibitory Mechanism ◽  
Object Movement ◽  
Moving Stimulus ◽  
Homogeneous Environment

1. One large neurone on each side of the cervical and thoracic ventral nerve cord of crickets responds to object motion anywhere in the visual field of the ipsilateral compound eye, but not to the forced or voluntary movement of the eye itself. 2. This discrimination between self-movement and object-movement is accomplished by an inhibitory mechanism mediated by the same eye. 3. Inhibition must be present because a potent moving stimulus becomes ineffective if presented during a forced eye movement. 4. Its visual origin is demonstrated in two ways: (a) abolishing all known mechanosensory feedback does not disrupt the mechanism, but (b) alteration of visual conditions does so in a predictable way. Sweeping the eye past a complex visual environment suppresses the neurone's response to a concurrently or subsequently presented moving target, whereas the same movement past a simplified or homogeneous environment produces little or no inhibition. 5. Responses to eye movement itself are greatly enhanced in appropriately simplified visual fields, reinforcing the conclusion that the inhibition preventing response in complex fields is of visual origin. 6. Suggestive evidence for an additional inhibitory mechanism associated with voluntary movement is presented.

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