OPTICAL SYSTEM AND IMAGE PICKUP APPARATUS

原文（中国語）

An optical system includes first to third units. The first unit includes a first substrate and a first lens having negative refractive power. The first lens is disposed on the image side of the first substrate. The second unit includes a second substrate and a second lens having positive refractive power. The second lens is disposed on the object side or image side of the second substrate. The third unit includes a third substrate and a third lens having positive refractive power. The third lens is disposed on the object side or image side of the third substrate. At least one of the first to third lenses constitutes a cemented lens including a fourth lens. The fourth lens and the lens cemented with the fourth lens in the cemented lens have refractive powers different from each other and Abbe numbers different from each other.