Patent ID: 8014074

Claim:
A finder optical system comprising: an erecting image forming member configured to convert a subject image formed by an image taking lens into an erecting image, and an ocular lens configured to enable observation the erecting image of the subject image therethrough, wherein said ocular lens includes, in an order from said erecting image forming member side to the observation side, a first lens group of negative refracting power, a second lens group of positive refracting power and configured to move in an optical axis direction to perform diopter adjustment, and a third lens group having at least one positive lens and at least one negative lens and having a positive or negative overall refracting power, and wherein, when a focal length of the finder optical system as said ocular lens is at −1 diopter is denoted by f, a composite focal length of the negative lens or lenses of said third lens group is denoted by f 3 n , a conditional expression −0.55 <f 3 n/f<− 0.30 is satisfied.