An optical system includes, in order from an object side toward an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power. A distance between consecutive ones of the lens units changes when focusing is performed. The first lens unit is stationary during focusing. The second lens unit is moved toward the image side when focus is changed from an object at infinity to an object at a short distance. Lateral magnification β2 of the second lens unit when focusing on the object at infinity, focal length f1 of the first lens unit, and focal length f2 of the second lens unit are set appropriately to satisfy predetermined mathematical conditions.

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.

A camera lens module in which an optical system is configured to include five sheets of lenses is provided. In the camera lens module, first, second, third, fourth and fifth lenses are sequentially arranged from an object side, and the first lens performs a zooming operation while moving along an optical axis. Accordingly, the optical system is configured to include five sheets of lenses for performance of a zooming operation and to allow only the first lens to perform the zooming operation, so that it is possible to manufacture a high-resolution optical system in a compact size and to perform the zooming operation at a high speed.

A lens apparatus includes an imaging optical system includes an imaging optical system including a plurality of lenses, a first holding member holding at least a first lens closest to an object among the plurality of lenses, and configured to move in an optical axis direction of the imaging optical system to perform focusing, a barrel member provided on an outside of the first holding member, and a control unit configured to control a driving unit configured to move the first holding member. When focus is at infinity, an edge surface on an object side of the barrel member is positioned on the object side of a surface vertex of an object-side surface of the first lens. When focus is at infinity, an edge surface on the object side of the control unit is positioned on the object side of the surface vertex.

A zoom lens system includes a positive first lens group, and a rear lens group behind the first lens group, in that order from the object side. The first lens group includes at least one positive single lens element, a negative meniscus lens element having a convex surface on the object side, and at least one positive lens element, in that order from the object side. A distance between the first lens group and the rear lens group increases upon zooming from the short to long focal length extremities. The following conditions (1) and (2) are satisfied:

fG1/fn<−1.50  (1), and

65<νp.sub.ave  (2),

wherein fG1 designates the focal length of the first lens group, fn designates the focal length of the negative meniscus lens element, and νp.sub.ave designates the average value of the Abbe numbers with respect to the d-line of the positive lens elements.

An optical zoom in a small form factor suitable for use in mobile devices such as cell phones, security cameras, and other small-scale imaging systems. One or more Alvarez lens pairs are provided, and moved transversely to the optical axis. The combination of one or more Alvarez lens pairs and the actuator permits a zoom power of at least 3× with a lateral displacement distance of the optical components of approximately five millimeters or less.

An image forming lens is formed by sequentially arranging, from an object side to an image side, a first lens group having positive refractive power, an aperture stop, and a second lens group having positive or negative refractive power. The image forming lens satisfies a conditional expression:
0.15<D1a/D1<0.50, where D1a is an air space between the first positive lens and the second positive lens in the first lens group, and D1 is a distance on an optical axis from an object-side lens surface of the first positive lens to an image-side lens surface of the third positive lens in the first lens group.

A zoom lens includes in order from an object side to an image side along an optical axis a first lens group having a positive refractive power, including a first lens disposed along the optical axis, and a second lens group having a negative refractive power, including a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens disposed in order along the optical axis. Positions of the second lens to the seventh lens on the optical axis can be changed to achieve continuous zooming of the zoom lens. A total effective focal length ft of the zoom lens when it is in a final state and a total effective focal length fs of the zoom lens when it is in an initial state satisfy 1.3<ft/fs<1.5.

The disclosure provides a camera lens group, which sequentially includes, from an object side to an image side along an optical axis: a first lens group with a positive refractive power, sequentially including, along the optical axis, a first lens, a second lens and a third lens with refractive power respectively; and a second lens group with a negative refractive power, sequentially including, the optical axis, a fourth lens, a fifth lens, a sixth lens and a seventh lens with refractive power respectively, wherein a total effective focal length f of the camera lens group and an entrance pupil diameter (EPD) of the camera lens group meet f/EPD<1.4; and an effective focal length f1 of the first lens and a spacing distance T34 of the third lens and the fourth lens on the optical axis meet 3.0<f1/T34<5.0.

The present invention discloses a portable zoom microscope, comprising a case (15) and an optical system assembly installed in the case (15), characterized in that the optical system assembly comprises an objective I (1), an objective II (2), an eyepiece III (3), an eyepiece II (4) and an eyepiece I (5) arranged in sequence along an optical axis Z from an object plane to eyes, wherein the objective I (1) is a positive lens, the objective II (2) is a negative lens, the eyepiece III (3) is a positive lens, the eyepiece II (4) is a positive lens, and the eyepiece I (5) is a negative lens, which effectively eliminates the longitudinal chromatic aberration and the lateral colour, so that the zoom microscope can distinguish the details of small objects more clearly and intuitively, greatly improving the image quality of products.