Matsushita Electric Industrial Co., Ltd.

Osamu Doi

Michihiro Yamagata

Yasuhiro Tanaka

Kenji Inoue

Jun Murata

Kazuhiko Noda

Hiromitsu Shimazaki

Hironori Taguchi

Hideki Yasuda

Akihiro Tsuru

Yoshihiro Gotou

In an objective lens for an optical head apparatus for reading or writing an information on a recording medium such as optical disc, astigmatism is added on axial wavefront aberration so that off-axis astigmatism is to be cancelled by the axial astigmatism. At least one surface of the objective lens is a toric or cylindrical surface, and a standard deviation of astigmatism component of axial wavefront aberration is defined as Wa is to be restricted in a range of 0&lt;Wa&lt;0.07.lambda. (.lambda. is a wavelength of a light to be used). When the objective lens moves in a radial direction of the optical disc, a light beam enters into the objective lens in an off-axis region where the aberration is compensated by the axial astigmatism.

Objective lens and optical head apparatus using the objective lens

A developing apparatus has a toner reservoir for holding a non-magnetic toner, a toner supply roller including a supply surface for receiving the toner from the toner reservoir and electrifying the toner thereon, an electrostatic latent image carrier including a curved or flat latent image surface on which a latent image formed by an electrostatic voltage distribution thereon is developed by the toner transferred from the supply surface, and a toner seal surface arranged adjacent to the toner supply roller to contact a remaining part of the toner on the supply surface after the latent image development so that the remaining part of the toner is taken into the toner reservoir. The respective frictional coefficients between the toner seal surface and the toner and between the toner particles are selected to prevent a disturbance of toner condition between the toner and the toner seal surface.

Apparatus for developing an electrostatic latent image with a

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Nara, Japan

Osamu Doi