Optical System and Optical Instrument, Image Pickup Apparatus, and Image Pickup System Using the Same

An optical system which forms an optical image on an image pickup element including a plurality of pixels arranged in rows two-dimensionally, which converts a light intensity to an electric signal, and a plurality of color filters disposed on the plurality of pixels respectively, comprising in order from an object side,

• a first lens unit having a positive refractive power, which includes a plurality of lenses,
• a stop, and
• a second lens unit which includes a plurality of lenses, wherein
• lens units which form the optical system include the first lens unit and the second lens unit, and
• the first lens unit includes a first object-side lens which is disposed nearest to an object, and
• the second lens unit includes a second image-side lens which is disposed nearest to an image, and
• the first lens unit includes a negative lens, and a positive lens which is disposed on the object side of the negative lens, and
• the following conditional expressions (15), (16), (19), and (20) are satisfied:
• β≦−1.1 (15)
• 0.0<NA (16)
• 1.0<WD/BF (19)
• 0.5<2×(WD×tan(sin−1 NA)+Yobj)/φs<4.0 (20)
• where,
• β denotes an imaging magnification of the optical system,
• NA denotes a numerical aperture on the object side of the optical system,
• WD denotes a distance on an optical axis from the object up to an object-side surface of the first object-side lens,
• BF denotes a distance on the optical axis from an image-side surface of the second image-side lens up to the image,
• Yobj denotes a maximum object height, and
• φs denotes a diameter of the stop.