Patent – EF 28 f/1.8 DO & Others

Canon files patent for new DO lenses

• Patent publication 2009-198960
• Published 03/09/2009
• Filing date 2008/02/25

Example 1

• Focal length f = 27.14mm
• Fno = 1.85
• Angle of 77.1 °

Example 2

• Focal length f = 24.50mm
• Fno = 1.45
• Angle of 82.9 °

Example 3

• Focal length f = 25.00mm
• Fno = 1.45
• Angle of 81.8 °

Example 4

• Focal length f = 24.33-36.50-47.00mm
• Fno = 3.4-4.0-4.7
• 83.3-61.3-49.4 ° angle

Example 5

• Focal length f = 26.00-39.00-50.23mm
• Fno = 3.4-4.0-4.7
• 79.5-58.0-46.6 ° angle

Information

• General retrofocus
• In general SLR wide angle lens
• Many chromatic aberration
• Using high-dispersion glass, as excessive compensation around
• General diffractive optics
• Can correct chromatic aberrations
• Where it is difficult to use
• Manufacturing difficulties
• Aberration can not fine-lattice

Patented Features

• Adopted retrofocus
• Chromatic aberration correction over the entire
• Diffractive optical elements, aspherical and low dispersion, employing anomalous dispersion lens
• The lenses focus mechanism
• Front lens is fixed
• Second lens to focus
• Floating mechanism
• The optical system of patents
• Lateral chromatic aberration to occur around the first lens
• Not easily corrected by increasing the number of lenses
• Diffractive optics correction to put the image side than the diaphragm
• Only increase the power of the diffractive optical element
• Chromatic aberration correction using a bonded lens

This is an older patent application, but I think it's still important to see diffractive optics are not dead within Canon R&D.

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