Abstract: There is disclosed a camera equipped with a mode setting device which counts the number of uses of each of plural modes, and sets the most frequently used mode as the initial mode. At the phototaking operation, the camera is set at such most frequently used mode. The above-mentioned plural modes can be plural exposure control modes, focal length control modes, photographing magnification setting modes, self-timer modes, automatic exposure value correcting modes, or alarm modes.

Abstract: A composite diamond grain which comprises a heat-resistant grain as a nucleus and discrete diamond crystal particles distributed on the surface of the grain or diamond crystal films formed to cover the entire surface of the grain and a method for producing the composite diamond grain by the vapor-phase process are disclosed. For the filament method which is one form of the vapor-phase method, tantalum is useful as the material for the filament. Since tantalum is susceptible of embrittlement by hydrogen, a treatment to be performed on tantalum for the elimination of this drawback is also disclosed.

Abstract: An optical system includes a forward group having a first lens group of positive focal length and a seconds lens group of negative focal length, the forward group having a positive focal length, a stop, and a rearward group having a positive focal length. The forward group, the stop and the rearward group are disposed in the named order from the object side. The spacing between the first lens group and the second lens group may be varied along the optic axis to thereby fluctuate the spherical aberration and coma of the optical system and vary the depictive property of the image of the defocus area and also, fluctuate the astigmatism of the optical system following the fluctuations of the spherical aberration and coma, thereby maintaining the flatness of the image plane. The optical system is constructed so as to satisfy the following conditions:0.5<.vertline.f.sub.2 /f.vertline.<1.00.5<.vertline.f.sub.1 /f.sub.2 .vertline.<1.

Abstract: A Gauss type rear focus lens includes a forward group having, in succession from the object side, a first lens component having its convex surface facing the object side and having a positive refractive power, a second lens component comprised of at least one lens and having a positive refractive power, and a third lens component having its sharply concave surface facing the image side and having a negative refractive power, the forward group having a positive refractive power as a whole, and a rearward group disposed on the image side relative to the forward group, the rearward group having a fourth lens having its sharply concave surface facing the object side and having a negative refractive power, a fifth lens having its sharply convex surface facing the image side and having a positive refractive power, and a sixth lens having a positive refractive power, the rearward group having a positive refractive power.