A photographic optical system including a beam splitter for a finder is provided with a releasably attached extender in between the beam splitter and a focal plane, while the finder is provided with means for changing the magnification of an image thereof as the extender is inserted into, or retracted from, axial alignment to the optical system. The camera has, despite the addition of the magnification power changing capability along with the finder image magnification correcting capability, to be made small in the size and light in the weight.