Erect Image Research Articles

An Optimized Zoom Ophthalmoscope

An indirect ophthalmoscope that could provide higher magnification (up to 15X) would offer definite advantages in fundus diagnosis. If it could also supply an erect fundus image, it could advantageously replace the surgical microscope in vitrectomy operations. The surgical microscope requires the use of a contact lens, which restricts the surgical techniques and may damage the corneal epithelium, and it reduces image brightness when the magnification is increased. In contrast, an indirect ophthalmoscope does not require a contact lens and keeps the image brightness constant regardless of magnification. Increased magnification can be obtained in an indirect ophthalmoscope by incorporating telescopes in the ophthalmoscope oculars. The possible use of two telescopic systems, Keplerian and Galilean, and the problems of stereopsis and image inversion are discussed. A new, optimized ophthalmoscope is described, with Keplerian telescopes, that provides a range of magnifications from 2X to 15X as well as options for an erect or inverted fundus image.

All-spherical catadioptric telescope with small corrector lenses

A well-corrected telescope with a large spherical primary mirror can be realized by using three or four small, widely spaced, corrector lenses. An interesting solution uses the lenses in a relay configuration which results in an erect image, accessible real exit pupil, and an internal field stop. Lateral color is corrected by adding a field lens at an intermediate focus. Polychromatic axial correction is excellent despite use of only one type of glass. The useful field of view is typically limited to 1 deg. Examples are presented.

Application of gradient-index fiber arrays to copying machines

A gradient-index fiber array arranged in a plurality of rows, which forms an erect image with unit magnification, is employed as a novel optical system for use in a copying machine. In this paper, the optical characteristics of the fiber array are discussed. In particular, an equation indicating the quantity of light for slit-exposure scanning is introduced. The f/No. of the N-row array is defined in a form equivalent to the f/No. of a conventional lens.

Some radiometric properties of gradient-index fiber lenses

Some radiometric properties of gradient-index fiber lenses and lens arrays are explored. Consideration is restricted to the paraxial region of fibers that produce erect images at unit magnification. In two instances the radiometric properties of these lenses and lens arrays are considerably different from the properties of conventional (nongradient) lenses. First, the off-axis image plane irradiance for a single gradient-index fiber falls off far more rapidly than the familiar cos(4) law. Second, the exposure (integrated image irradiance) for a fiber array is independent of the object-to-image distance.

The Refractive Index Gradient in the Crystalline Cones of the Eyes of A Euphausiid Crustacean

ABSTRACT The eyes of the euphausiids, a group of malacostracan Crustacea, show a remarkable similarity to the superposition (Exner, 1891) eyes of moths. In both groups the eye has an outer layer of crystalline cones, a wide clear zone, and a layer of rhabdomes beneath it, whose radius of curvature is about half that of the eye itself (Fig. 2 a). We demonstrated recently that image formation in these eyes is indeed performed by a refracting superposition mechanism (Land, Burton & Meyer-Rochow, 1979), as supposed by Chun (1896). That is to say, light is bent by the crystalline cones in such a way that a ray reaching the outer surface of a cone, and making an angle α with the cone axis, is bent in the cone through an angle 2α (Fig. 1). This is the condition necessary if all parallel rays are to be brought to a focus in the rhabdome layer, where an erect image is produced (see Horridge, 1975). This mechanism, shared by moths, fireflies and some other beetles, is not the same as that of the decapod shrimps and prawns, where essentially the same trick is performed not by refracting cones, but by mirrors (Vogt, 1977; Land, 1978). Kampa (1965) proposed that the euphausiid eye was basically of the apposition type, with the cones funnelling light down light guides into the rhabdomes. However, the cones send light, as noted above, and the light-guides are not present (Meyer-Rochow & Walsh, 1979).

Close-up imaging of documents and displays with lens arrays

An unusually short close-up imaging system about 8.5 cm (3 (3/8) in.) long has been developed for document copiers, oscilloscope cameras, and computer peripheral hard-copy cameras. Arrays of simple lenses are molded in rows and columns on two parallel plastic lens plates. Each lens on the first lens plate forms a demagnified, inverted, intermediate image of a small area of the object in the space between lens plates. Each lens in the second plate erects and magnifies an intermediate image and places the resulting final image in partially overlapped registration with adjacent images, forming an erect uniform composite image of the whole object.

The superposition eye of skipper butterflies

1. The anatomy of the eye is described in seven representative genera of Australian Hesperioidea. Between the crystalline cones and the long rhabdom is a wide clear zone crossed by narrow extensions of the retinula cells. The distal pigment remains between the cones even in daylight. 2. No evidence of functional light guides crossing the clear zone could be found. 3. A real erect image is formed on the receptor layer. The acuity and origin of this image were investigated by several methods. 4. The angular sensitivity curve of the receptors is 6 to 8°wide at the 50% sensitivity contour. 5. Optomotor experiments with stripes of differing widths show that the angular sensitiv­ity of the receptors is fully utilized behaviourally, and that the eye functions in relatively dimlight. Adaptation changes are small. 6. A parallel beam falling on the eye reaches a single receptor via a circular patch of facets subtending about 30° at the centre of the eye. This was directly demonstrated by recording from a retinula cell and stimulating the eye by a moveable slit of parallel rays. This also demonstrates the wide acceptance angle of the exposed ends of the rhabdom columns. 7. When the eye is illuminated by a parallel beam, light is reflected back out of the eye. All the reflected light is contained in an angle of ±5° to the incident beam, although it enters and emerges via the large patch of facets mentioned above (6). Again, no effects of adaptation were observed. 8. The relation between the direction in which a ray enters the optical system of the cornea and cone and the direction it leaves was measured directly by a rotatable microscope of narrow aperture. 9. The mechanism by which the optical system forms the erect image on the receptor layer was demonstrated by tracing rays through scale drawings of the components. To do this the refractive index was measured in all components. The corneal surface acting as a lens forms the first image within the cone. The crystalline cone is non-homogeneous and acts as second lens in each ommatidium. 10. The skipper eye therefore illustrates Exner’s superposition principle, and it does so in daylight.

Calculation of the Optical Effects of a 275-m Spherical Mirror

People standing under a large spherical mirror see the world inverted, hanging above them as a real image. The shape of this image world depends upon where on the floor the observer stands. In this paper formulas for calculating image positions as a function of observer position are derived and depicted in diagrams of typical image worlds. The images formed by light reflecting several times in the mirror are also calculated. There are both an erect real image world and doubled rings of inverted images surrounding the single-reflection image world.

Alternatives to superposition images in clear-zone compound eyes

The clear zone between the cones and the receptor layer in dark -adapted eyes of insects that are active in dim light has formerly been explained as a space to allow formation of a superposition image. Although erect images have been seen in Ephestia (Lepidoptera) and Hydrophilus (Coleoptera), new experiments show that they are accompanied by scattered light and that the angular sensitivity of individual receptors must be wide in the dark-adapted state. Alternatives to the superposition theory are examined, and it is concluded that in eyes with crystalline cones the clear zone (in general, in the numerous shapes and sizes of eyes of nocturnally active insects) enables light entering by many facets to sum upon individual receptors on the far side of the clear zone. In addition to the scattered light effect, light is carried across the clear zone in crystalline tracts or retinula cell columns, which provide a separate optical pathway for each ommatidium also in the light-adapted state.

Pseudopupil phenomena in the compound eye of drosophila

In the compound eyes of the fruitflyDrosophila, the dioptric system of each ommatidium is able to form virtual images of the receptor terminals (rhabdomere tips) throughout the whole depth of the eye. It is shown (§ 3) that 3 characteristic superposition phenomena occur for images formed by distinct ommatidia (Figs. 3b and 5). The most remarkable superposition appears at the point where the optical axes of all ommatidia converge (center of curvature of the eye). At this level, highly magnified virtual and erect images of corresponding rhabdomeres are superimposed, giving rise to adeep pseudopupil (Fig. 9). Since in the ommatidia ofDrosophila the rhabdome shows a pattern of 7 distal endings (Fig. 8a), the resultingdeep pseudopupil consists of 7 light spots with a similar pattern (Figs. 8b, 7, 11). Conversely thedeep pseudopupil of compound eyes which have fused rhabdomes consists of a single light spot (Fig. 19). Such pseudopupils can be best observed either with antidromic or with orthodromic illumination of the eye, according to the specific transmission or reflection properties of the rhabdomes. Thedeep pseudopupil of Dipterans is not to be confused with thecorneal pseudopupil (Fig. 13 a) and especially not with thereduced corneal pseudopupil observed with a reduced aperture of the microscope (Fig. 13 b), in spite of the remarkable similarity of these phenomena regarding the asymmetry and the dimension of their pattern (comp. Figs. 7 and 13b). Thereduced corneal pseudopupil consists of 7 facets whereas thedeep pseudopupil consists of 7 virtual images of the receptor endings. From the results of Kirschfeld (1967), the appearance of areduced corneal pseudopupil like Fig. 13 b on the eye ofDrosophila proves that 7 receptors located in 7 neighbouring ommatidia look in the same direction in space (Fig. 14). The existence of such an optical arrangement favors the view that the eye ofDrosophila, like that ofMusca, belongs to the "neural superposition type". A comparative study between thedeep pseudopupil and thereduced corneal pseudopupil leads to the following geometric relation, which is specific of theDrosophila eye and probably of all compound eyes of the "neural superposition type": % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaaca% WGebaabaGaamyzaaaacqGH9aqpdaWcaaqaaiaadkfaaeaaceWGMbGb% auaaaaGaaiilaaaa!3B44! $$\frac{D}{e} = \frac{R}{{f'}},$$ , whereD is the diameter of a facet,e the distance between the centers of two neighbouring rhabdomere endings,R the radius of curvature of the eye, andf? the focal length (in air) of a corneal lens. Other types of pseudopupils, commonly appearing as dark spots in compound eyes, are explained on a basis similar to thedeep pseudopupil of Drosophila (§5). In fact, the dioptric system of an ommatidium can give virtual images not only of its distal receptor endings but of the whole intensity distribution (i.e. the whole "luminous structure") which is present in its internal focal plane. If this structure is simple, thedeep pseudopupil, resulting from superpositions of virtual images, is likewise simple (Figs. 16 and 17). If the "luminous structure" is complex, as for example in the eye of the butterflyVanessa (Fig. 18a schematized in Fig. 18c), then thedeep pseudopupil shows the same complexity (Fig. 18 b and d). In compound eyes which lack screening pigment between their crystalline cones, one can seesecondary pupils of the 1st and 2nd order as described by Exner. Again they may be explained by superpositions of virtual images in the depth of the eye, according to Fig. 20. Moreover, thedeep pseudopupil of the "optical superposition eye" may be due to the fact that the more distal converging system of an ommatidium forms virtual images not of the rhabdome endings themselves but of real images of these endings (Fig. 21). Although the phenomenon of thedeep pseudopupil is not perceived by the animal, it is of interest for the experimenter who can use it: 1) to study the light receptors easily in the eye of live and intact animals, 2) to measure the physiological divergence angle between adjoining ommatidia, 3) to study the movement of the visual axis and the retinomotor adaptation of the receptors, and 4) to stimulate simultaneously manycorresponding receptors belonging to different ommatidia. The advantages of thisin vivo technique are discussed in § 6.3.

Eye Glow in the Moth and Superposition Theory

EXNER'S theory of the formation of a retinal image by superposition1 in certain arthropod compound eyes requires that an object in front of a number of ommatidia is twice inverted by the dioptric system of each ommatidium. Thus erect images of the object are formed behind the crystalline cones. Converging proximally, those images grow in size and superimpose in the layer of the receptive structures, the rhabdoms. Exner tested his theory by observing the image formation in sectioned eyes and found agreement between experiment and theory in more than a dozen insect species. His findings were confirmed repeatedly using the firefly2–4. (Although Exner proposed the formation of superposition images in certain Crustacean eyes, he failed to obtain upright and superposition images. So did other observers2,3. Crustacea will therefore be excluded.)

Function of insect compound eyes containing crystalling tracts.

Image formation is studied in compound eyes of insects that contain crystalline tracts. In optical experiments the course of light is studied in fresh scalps of dark-adapted eyes using point and extended sources. In the tract region a point source gives a diffusely lighted area within which are punctate spots about 10 times brighter. Because the position of these spots does not change when the source is moved, and because their spacing agrees with estimates based on the known scalp depth, we conclude that these spots represent light radiating from the cut ends of tracts. An extended source gives a dim erect image in the tract region that may come from the pattern of illumination radiating from the cut ends of the tracts. In electrophysiological experiments intracellular microelectrode recordings of responses to illumination are made from single retinular cells of the skipper, Epargyreus clarus, an animal that lacks iris pigment. Measurements of visual fields of single retinular cells by three methods give half-power beam widths of about 2 degrees . Though not conclusive, these experiments suggest that only the light contained in the tract is effective in stimulating the retinular cell. This agrees with the theoretical study of Allen (1968) and is inconsistent with the superposition theory of Exner (1891) as applied to certain moth and skipper eyes.

Pigment Movement and the Crystalline Threads of the Firefly Eye

THE compound eye of the firefly is the one outstanding example which shows evidence of an image which is formed by the combination of rays that have entered by several facets. The original account by Exner1 includes a description and photograph of the erect image that can be found behind the cleaned cornea of the firefly Lampyris. This image has been confirmed by others2 and a theoretical explanation of it supposes that an inverted first image is formed within each corneal cone by the curvature of its front surface and that an erect second image is then formed by the curved surface of the proximal tip of the corneal cone3. The erect superposition image, however (which undoubtedly exists if the cornea is well cleaned), does not lie in the place of the receptors4 and there is no evidence that it has a functional significance. In fact, the superposition theory depends on the unlikely existence of an optically homogeneous and transparent region between the cornea and the layer of receptors. Despite its importance to the theory, the anatomy of the firefly retina remains unknown. The following account, based on Photuris versicolor, points to the conclusion that the superposition theory is applicable only to a cleaned cornea because the actual anatomy suggests quite a different optical system.

An industrial instrument for the observation of very-high-speed phenomena

The purpose of this instrument is to facilitate the observation and recording of objects moving at very high speeds and events taking place in extremely short times. In particular, it is intended to enable very fast repetitive motion to be observed stroboscopically, and such transient phenomena as burning high explosives to be recorded photographically.The equipment described has been designed in conjunction with an experimental image convertor tube (a development of type ME1201), and is intended as part of a comprehensive unit to exploit inherent capabilities.The static conditions necessary for focusing are discussed. Using the method desciibed, a resolution of 20 television lines/mm can be obtained at the image on the screen, with an electronic magnification variable between ×4and ×3/4. The focusing system used enables an erect image to be formed at certain magnifications.The arrangements for controlling the photographic exposure are described. Two alternative arrangements are available. The first is aimed at providing the shortest possible exposure for transient events; an effective shutter opening time of 1/20 microsec has been reached. In the second system, for stroboscopic observation, exposures down to one microsec are available at repetition rates up to 100 kc/s.In some applications a time-scale is desirable. This can be provided by moving the image across the screen at a known velocity. Three methods of producing a time scale in this manner are described. By these means writing speeds on the screen varying between 10 mm/sec and 90 km/sec can be obtained. The slower deflections, up to 500 m/sec, are virtually linear with time, while the faster speeds are obtained by using portions of either a continuous or damped-train sinusoidal deflection.Finally, some of the further developments of the equipment are reviewed, which preliminary experiments have suggested as being both possible and desirable.