An optical system and a projection device are provided. The optical system includes a display unit, a first lens group, a second lens group, and a reflector in sequence along a transmission direction of light; both the first lens group and the second lens group have positive focal powers; the optical system satisfies the following relationship: 0.01≤|φ.sub.100|≤0.02 and 0.005≤|.sub.φ200|≤0.015; φ.sub.100 represents a focal power of the first lens group, and φ.sub.200 represents a focal power of the second lens group.

This variable magnification optical system comprises a front lens group and a rear lens group, which are arranged in order from the object side along an optical axis, and the rear lens group comprises a first focusing lens group having positive refractive power, and a second focusing lens group disposed on the image surface side of the first focusing lens group and having negative refractive power. When the magnification is changed, the spacing between lens groups adjacent to each other changes, at the time of changing from focusing on an object at infinity to focusing on an object at a short distance, the position of the front lens group is fixed, the first focusing lens group and the second focusing lens group respectively move to the image surface side along different trajectories, and the following conditional expression is satisfied. 0.05<(−fF2)/ft<0.50 where fF2 is the focal length of the second focusing lens group, and ft is the focal length of the variable magnification optical system in a telephoto end state.

A lens apparatus includes an optical system including a front lens group having a positive refractive power and configured to move to an object side during focusing from infinity to a close-distance object, and a rear lens group arranged on an image side of the front lens group and configured to be immovable during focusing, a motor configured to move the front lens group, and a holding member including a flange portion, on the object side, extending in a direction orthogonal to an optical axis of the optical system and configured to hold at least part of the rear lens group, wherein the motor includes a coil, a casing housing the coil, and a shaft portion extending from the casing in an optical-axis direction of the optical system, and arranged at a position at which an end surface on the image side of the casing is on the object side with respect to the flange portion in the optical-axis direction.

An optical system includes, in order from an object side to an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power, wherein the first lens unit moves and the second lens unit does not move during focusing, wherein the first lens unit includes a positive lens arranged closest on the object side of the first lens unit, wherein the second lens unit includes three or more lenses including at least two negative lenses, wherein the first lens unit consists of a first subunit having positive refractive power, a second subunit having negative refractive power, and a third subunit having positive refractive power arranged in order from the object side to the image side, and wherein predetermined conditional expressions are satisfied.

An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, and a second lens unit having a positive refractive power. An interval between the first lens unit and the second lens unit changes during focusing. The second lens unit includes, in order from the object side to the image side, a first subunit having a positive refractive power, an aperture stop, and a second subunit having a positive refractive power. A predetermined condition is satisfied.

The disclosure provides a combined zoom dual-camera lens assembly, which includes a first lens group and a second lens group, wherein a field of view of the second lens group is larger than a field of view of the first lens group, and a thickness of the second lens group is smaller than a thickness of the first lens group; and a total effective focal length f.sub.T of the first lens group and a total effective focal length f.sub.W of the second lens group meet f.sub.T/f.sub.W>9.00.

A self-temperature focus compensation device adapted to cooperate with a lens group and including at least one Fresnel lens group is provided. Each Fresnel lens group has zero focal power at a specific temperature and is a cemented lens. Each Fresnel lens group includes a first Fresnel lens and a second Fresnel lens. The first Fresnel lens has positive focal power. The second Fresnel lens has negative focal power. A sum of a focal power change of the at least one Fresnel lens group with a temperature change and a focal power change of the lens group with the temperature change is zero.

Provided are an optical lens assembly and an electronic apparatus including the optical lens assembly. The optical lens assembly includes a first lens group having positive refractive power, a stop, and a second lens group having positive refractive power that are arranged from an object side to an image side. The first lens group includes a first lens having negative refractive power and a meniscus shape convex toward the object side, a second lens having negative refractive power, and at least one other lens. The second lens group includes at least three lenses, and a lens of the second lens group closest to the image side has at least one inflection point.

An imaging lens includes a positive first lens group and a second lens group, which are continuous in order from the position closest to the object side, as lens groups. During focusing, the distance between the first lens group and the second lens group changes. A stop is disposed closer to the image side than a lens which is second from the object side. A combined refractive power of all lenses closer to the object side than the stop is positive. The imaging lens includes an LA positive lens and an LB positive lens that satisfy a predetermined conditional expression at a position closer to the object side than the stop. An Abbe number of the LB positive lens is the maximum among Abbe numbers of all positive lenses closer to the object side than the stop.

An imaging lens includes a positive first lens group and a second lens group, which are continuous in order from the position closest to the object side, as lens groups. During focusing, the distance between the first lens group and the second lens group changes. A stop is disposed closer to the image side than a lens which is second from the object side. A combined refractive power of all lenses closer to the object side than the stop is positive. The imaging lens includes an LA positive lens and an LB positive lens that satisfy a predetermined conditional expression at a position closer to the object side than the stop. An Abbe number of the LB positive lens is the maximum among Abbe numbers of all positive lenses closer to the object side than the stop.