Canon Patent: 400mm F4 TC DO And 600mm F4 TC DO Lenses

Here is a new Canon patent. One that will for sure start some bs rumors ;-)

This Canon patent application discusses optical formulas and methods for two lenses with diffractive optical elements:

• 400mm F4 TC DO
• 600mm F4 TC DO

From the patent literature:

• To provide an optical system having a short overall length and in which a magnification conversion optical group can be inserted and removed.
• Description of the Related Art: One method for changing the focal length of an optical system used in imaging is to insert a magnification conversion optical group such as an extender into the optical path. As an optical system in which the overall length (the distance from the optical surface closest to the object to the image plane) does not change by inserting or removing the magnification conversion optical group, Patent Document 1 discloses an optical system in which a magnification conversion group can be inserted or removed at a position where an axial light beam between an aperture stop and an image plane converges.
• However, providing a space between the aperture stop and the image plane to insert a magnification conversion optical group as in Patent Document 1 increases the overall length of the original optical system. Also, inserting a magnification conversion optical group in a narrow space may increase various aberrations in the optical system.
• The present invention provides an optical system in which a magnification conversion optical group can be inserted or removed, yet which has a short overall length and provides good optical performance.
• In each cross -sectional view, O represents the optical axis, IP represents the image plane, and G represents a glass block such as a quartz low-pass filter or an infrared cut filter. In Examples 1 and 2, Ldoe represents a diffractive optical element , and asph represents an aspheric surface. In both Examples 1 and 2, the diffractive surface of the diffractive optical element Ldoe is provided on the cemented surface of the second cemented lens counting from the object side. The aspheric surface asph is provided on the object-side optical surface of the positive lens closest to the object side.

Example 1

• Focal length: 392.58
• F-number: 4.12
• Half angle of view: 3.45
• Image height: 21.64
• Total length: 280.33
• Back Focus: 36.01

Example 2 (Example 1 with teleconverter inserted)

• Focal length: 549.72
• F-number: 5.77
• Half angle of view: 2.25
• Image height: 21.64
• Total length: 280.33
• Back Focus: 36.00

Example 3

• Focal length: 585.00
• F-number: 4.12
• Half angle of view: 2.12
• Image height: 21.64
• Total length: 467.45
• Back Focus: 55.5

Example 4 (Example 3 with teleconverter inserted)

• Focal length: 819.18
• F-number: 5.77
• Half angle of view: 1.51
• Image height: 21.64
• Total length: 467.45
• Back Focus: 55.50

More Canon patents are listed here.

[via asobinet]