Zoom optical system

A zoom optical system, comprising:

• a first lens group comprising a negative refractive power;
• a second lens group comprising a positive refractive power;
• and
• a third lens group comprising a positive refractive power,
• wherein
• the first to third lens groups are sequentially disposed from an object side toward an imaging plane,
• upon zooming from a wide-angle position to a telephoto position, a gap between the first and second lens groups is decreased,
• a gap between the second and third lens groups is adjustable,
• the first lens group comprises a first lens and a second lens, the second lens group comprises a third lens, a fourth lens having a convex object-side surface, and a fifth lens having a convex object-side surface, and the third group comprises a sixth lens, and
• 1.9≤|fG1/fw|≤3.0, 4.0<ft/fw<7.0, and 1.61<n4<1.68, where fw is an overall focal length of the zoom optical system in the wide-angle position, fG1 is a synthesized focal length of the first lens group, ft is an overall focal length of the zoom optical system in the telephoto position, and n4 is a refractive index of the fourth lens.