Lens device comprising light blocking means and an optical pickup apparatus using the lens device

A method for discriminating discs having different thicknesses, comprising the steps of:

• providing an objective lens for focussing light in a light path into a focal zone;
• preventing light in an intermediate axial region of said light path from reaching said focal zone, said intermediate axial region being located between a near axial region which includes a center of said light path and a far axial region located radially outward from said intermediate region;
• permitting light in said near and far regions of said light path to reach said focal zone;
• placing one of said at least two discs having different thicknesses in said focal zone;
• converting light in said near and far axial regions and reflected from said disc into electric signals using a quadrant photodetector;
• obtaining at least one of a sum signal and a focus error signal from said quadrant photodetector by increasing and decreasing focus current controlling an axial position of said objective lens a predetermined number of times;
• comparing said at least one of said sum signal and said focus error signal with a first reference value corresponding to a thin disc;
• determining that the disc is thin if said at least one of said sum signal and said focus error signal is greater than said first reference value;
• comparing said at least one of said sum signal and said focus error signal with a second reference value which is smaller than said first reference value only if said at least one of said sum signal and said focus error signal is smaller than said first reference value;
• and
• determining that the disc is thick if said at least one of said sum signal and said focus error signal is greater than said second reference value.

A method for detecting focus on at least two discs having different thicknesses, comprising the steps of:

• providing an objective lens for focussing light in a light path into a focal zone;
• placing one of said at least two discs having different thicknesses in said focal zone;
• preventing light in an intermediate axial region of said light path from reaching said focal zone, said intermediate axial region being located between a near axial region which includes a center of said light path and a far axial region located radially outward from said intermediate region;
• permitting light in said near and far regions of said light path to reach said focal zone;
• converting light in said near and far axial regions and reflected from said disc into electric signals;
• using, for focus detection, electric signals corresponding to both near and far axial regions when said light is reflected from a relatively thin disc;
• and
• using, for focus detection, electric signals corresponding to only said near axial region when said light is reflected from a relatively thick disc;
• and
• detecting focus based on said used electrical signals.

A method for reproducing information from at least two discs having different thicknesses, comprising the steps of:

• providing an objective lens for focussing light in a light path into a focal zone;
• preventing light in an intermediate axial region of said light path from reaching said focal zone, said intermediate axial region being located between a near axial region which includes a center of said light path and a far axial region located radially outward from said intermediate region;
• permitting light in said near and far regions of said light path to reach said focal zone;
• placing one of said at least two discs having different thicknesses in said focal zone;
• converting light in said near and far axial regions which is reflected from said disc into electric signals in an inner photodetector and in a outer photodetector surrounding said inner photodetector;
• using electric signals corresponding to both near and far axial regions converted in both said inner and outer photodetector when said light is reflected from a relatively thin disc;
• and
• using electric signals corresponding to near axial region converted in only said inner photodetector when said light is reflected from a relatively thick disc.

A method for recording information on at least two discs having different thicknesses, comprising the steps of:

• providing an objective lens for focussing light in a light path into a focal zone;
• placing one of said at least two discs having different thicknesses in said focal zone;
• preventing light in an intermediate axial region of said light path from reaching said focal zone, said intermediate axial region being located between a near axial region which includes a center of said light path and a far axial region located radially outward from said intermediate region;
• and
• permitting light in said near and far regions of said light path to reach said focal zone.