Abstract: An optical imaging system includes a first lens having an object-side surface that is convex; a second lens having a refractive power and a refractive index of 1.65 or more; a third lens having a refractive power; a fourth lens having a refractive power and an object-side surface that is convex; a fifth lens having a refractive power; a sixth lens having a positive refractive power; and a seventh lens having an object-side surface that is convex, wherein the first lens through the seventh lens are sequentially disposed in numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system, and two or more of the first lens and the third lens through the seventh lens have a refractive index of 1.6 or more.

Abstract: An optical imaging system includes a plurality of lenses disposed along an optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system. The lenses are separated from each other by respective air gaps along the optical axis between the lenses. The lenses include a first lens closest to the object side of the optical imaging system. The conditional expressions 1.5 mm<Gmax, TL<12.0 mm, and 0.15<R1/f are satisfied, where Gmax is a maximum air gap along the optical axis among all of the air gaps, TL is a length of the optical imaging system along the optical axis from an object-side surface of the first lens to the imaging plane, R1 is a radius of curvature of the object-side surface of the first lens, and f is a focal length of the optical imaging system.

Abstract: An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens sequentially disposed in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging surface of an image sensor, wherein a conditional expression f/f2+f/f3<?0.4 is satisfied, where f is a focal length of the optical imaging system, f2 is a focal length of the second lens, and f3 is a focal length of the third lens, and a conditional expression TTL/(2*IMG HT)<0.69 is satisfied, where TTL is a distance along the optical axis from an object-side surface of the first lens to the imaging surface of the image sensor, and IMG HT is one-half of a diagonal length of the imaging surface of the image sensor.

Abstract: An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens sequentially disposed in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging surface of an image sensor, wherein a conditional expression f/f2+f/f3<?0.4 is satisfied, where f is a focal length of the optical imaging system, f2 is a focal length of the second lens, and f3 is a focal length of the third lens, and a conditional expression TTL/(2*IMG HT)<0.69 is satisfied, where TTL is a distance along the optical axis from an object-side surface of the first lens to the imaging surface of the image sensor, and IMG HT is one-half of a diagonal length of the imaging surface of the image sensor.

Abstract: An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens sequentially disposed along an optical axis from an object-side surface of the first lens toward an imaging plane of an image sensor, wherein 3.5?TTL/IMG HT, f1+f2|<2.0 mm, and 0.7?L1S1es/L1S1el<1.0 are satisfied, where TTL is a distance along the optical axis from the object-side surface of the first lens to the imaging plane of the image sensor, IMG HT is one-half of a diagonal length of the imaging plane of the image sensor, f1 is a focal length of the first lens, f2 is a focal length of the second lens, L1S1el is a maximum effective radius of the object-side surface of the first lens, and L1S1es is a minimum effective radius of the object-side surface of the first lens.

Abstract: A negative electrode active material as well as a method of preparing a negative electrode active material which includes preparing a silicon-based compound including SiOx, wherein 0.5<x<1.3; disposing a polymer layer including a polymer compound on the silicon-based compound; disposing a metal catalyst layer on the polymer layer; heat treating the silicon-based compound on which the polymer layer and the metal catalyst layer are disposed; and removing the metal catalyst layer, wherein the polymer compound includes any one selected from the group consisting of glucose, fructose, galactose, maltose, lactose, sucrose, a phenolic resin, a naphthalene resin, a polyvinyl alcohol resin, a urethane resin, polyimide, a furan resin, a cellulose resin, an epoxy resin, a polystyrene resin, a resorcinol-based resin, a phloroglucinol-based resin, a coal-derived pitch, a petroleum-derived pitch, a tar and a mixture of two or more thereof.

Abstract: A silicon-carbon complex comprising carbon-based particles and silicon-based particles, wherein the silicon-based particles are dispersed and positioned on surfaces of the carbon-based particles, the carbon-based particles have a specific surface area of 0.4 m2/g to 1.5 m2/g, and the silicon-based particles are doped with one or more elements selected from the group consisting of Mg, Li, Ca, and Al, and a negative electrode active material for lithium secondary battery comprising the same.

Abstract: A lens, wherein a first profile in a first direction intersecting an optical axis and a second profile in a second direction intersecting the optical axis are different from each other, and a length of the first profile in the first direction is different from a length of the second profile in the second direction.

Abstract: An optical imaging system includes an optical system including at least six lenses, sequentially disposed from an object side toward an image side, an image sensor configured to convert light incident through the optical system into an electronic signal, and a variable stop configured to change an incident hole diameter and disposed toward the object side of a lens of the optical system closest to the object side, wherein TTL is a distance to an imaging plane of the image sensor from an object-side surface of the lens closest to the object side and 4.7 mm<TTL<6.00 mm, and wherein Ri is a radius of curvature of an object-side surface of a lens of the optical system second closest to the image sensor, Rj is a radius of curvature of an image-side surface of the lens that is second closest to the image sensor, and ?0.5<(|Ri|?|Rj|)/(|Ri|+|Rj|)<0.5.

Abstract: An optical imaging system includes: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens sequentially arranged from an object side. The optical imaging system satisfies 0.35<R1/f<0.40; N2+N3+N4>4.8; and TTL/(2*IMG HT) <0.70, where R1 is a radius of curvature of an object-side surface of the first lens, f is an overall focal length of the optical imaging system including the first to sixth lenses, N2 is a refractive index of the second lens, N3 is a refractive index of the third lens, N4 is a refractive index of the fourth lens, TTL is a distance from the object-side surface of the first lens to an image capturing surface of an image sensor, and IMG HT is half of a diagonal length of the image capturing surface of the image sensor.

Abstract: A method of providing a chat service in a map-based virtual space includes receiving a place selection signal based on map information and/or a motion detection signal from user terminals, determining location information and FoV information of the corresponding account in the virtual space, determining image information of a perspective view and one or more other accounts to be displayed on the corresponding user terminal, receiving a chat request from a first user terminal, receiving a result regarding whether to accept a chat in response to the chat request from a second user terminal, determining whether an account of the first user terminal and the other account of the second user terminal on the street view satisfy a preset condition, and providing the chat service between the first user terminal and the second user terminal based on whether the chat is accepted and whether the preset condition is satisfied.