Variable focal length optical system

A variable focal length system capable of shifting images, having object and image sides, comprising:

• a first lens group having a positive refractive power;
• a second lens group having a negative refractive power positioned adjacent to the first lens group on the object side;
• and
• a third lens group positioned adjacent to the first lens group on the image side;
• wherein a distance between the first and second lens groups is decreased and a distance between the first and third lens groups is changed when changing positions of the lens groups from a maximum wide-angle state to maximum telephoto state;
• the first lens group includes at least two sub-lens groups, one of the two sub-lens groups being moved in a direction almost orthogonal to an optical axis to shift an image along a direction almost orthogonal to the optical axis;
• and
• when fs is a focal length of the first lens group and fh is a focal length of the one of the sub-lens groups, the following condition is satisfied:
• 0. 3<fs/fh<0.6.

A variable focal length optical system capable of shifting images, having an object side, comprising in sequence from the object side:

• a first lens group having a positive refractive power;
• a second lens group having either a positive or a negative refractive power;
• a third lens group having a negative refractive power;
• a fourth lens group having a positive refractive power;
• and
• a fifth lens group having a negative refractive power;
• wherein at least the first and fifth lens groups are moved toward the object side when changing positions of the lens groups from a maximum wide-angle state to a maximum telephoto state so that a distance between the first and second lens groups is increased, a distance between the second and third lens groups is increased, a distance between the third and fourth lens groups is decreased, and a distance between the fourth and fifth lens groups is decreased;
• a sixth lens group forming a part of the fourth lens group is moved in a direction almost orthogonal to the optical axis to shift an image along a direction almost orthogonal to the optical axis;
• and
• when is .beta.5w is a lateral magnification of the fifth lens group in the maximum wide-angle state, .beta.5t is a lateral magnification of the fifth lens group in the maximum telephoto state, fw is a focal length of the total optical system in the maximum wide-angle state, and ft is a focal length of the total optical system in the maximum telephoto state, the following condition is satisfied:
• 0/4<(.beta.5t/.beta.5w)/(ft/fw)<0.7.