Zoom lens system, interchangeable lens apparatus and camera system

An interchangeable lens apparatus, comprising:

• a zoom lens system including a plurality of lens and performing zooming by changing intervals among the lens units;
• and
• a mount section connected to a camera body that includes an image sensor which receives an optical image formed by the zoom lens system thereby to convert the optical image to an electrical image signal, wherein
• the plurality of lens units, in order from an object side to an image side, includes:
• a first lens unit having negative optical power;
• a second lens unit having positive optical power;
• a third lens unit having positive optical power;
• and
• a fourth lens, and
• the following conditions are satisfied:
• 1.4<DL/YM<2.5 (10)
• 1.2<BFW/YM<1.6 (11)
• (where, 100<2ωW<140)
• where,
• DL is an effective diameter of the lens surface closest to the image side,
• BFW is the back focus at a wide-angle limit,
• YM is the maximum image height at a wide-angle limit, and
• ωW is a half view angle (°) at a wide-angle limit.

A camera system, comprising:

• an interchangeable lens apparatus that includes a zoom lens system including a plurality of lens units and performing zooming by changing intervals among the lens units;
• and
• a camera body which is connected to the interchangeable lens apparatus via a camera mount section in an attachable and removable manner and includes an image sensor which receives an optical image formed by the zoom lens system thereby to convert the optical image to an electrical image signal, wherein
• the plurality of lens units, in order from an object side to an image side, includes:
• a first lens unit having negative optical power;
• a second lens unit having positive optical power;
• a third lens unit having positive optical power;
• and
• a fourth lens, and
• the following conditions are satisfied:
• 1.4<DL/YM<2.5 (10)
• 1.2<BFW/YM<1.6 (11)
• (where, 100<2ωW<140)
• where,
• DL is an effective diameter of the lens surface closest to the image side,
• BFW is the back focus at a wide-angle limit,
• YM is the maximum image height at a wide-angle limit, and
• ωW is a half view angle (°) at a wide-angle limit.