An optical apparatus to be used for digital still cameras for setting any
one of a plurality of lenses in a picture taking (image capturing)
position comprising a lens turret rotatable around an axis and having the
lenses mounted thereon, a driving mechanism to rotate the lens turret so
that one of the lenses can be set at the picture taking position and a
means to adjust and extend the back focal length of the lens shaped like a
column or square column and made of glass, plastic or the like that has
higher refraction index than that of air. By said means of back focal
length adjustment, the position of the lens with shorter focal length can
be fixed on the lens turret moving apart from the image sensor like CCD or
C-MOS upward without changing its focal length itself, and fixed at the
same level thereon as the lens with longer focal length. With this
adjustment of back focal length, the lenses can be fixed on the turret as
closely as possible with each other, yet any part of one lens does not cut
in or disturb any part of light path of the other lens. Consequently the
total size of lens turret could be minimized.
