Patent: Canon EF 2.8x Teleconverter

Patent Time
A patent showing a new teleconverter has made an appearance. It appears to be a 2.7 or 2.8x TC. What effect woud it have on aperture? A 400 f/2.8L IS II would become 1120mm at f/8. All well and good, but the missing f/8 autofocus on the 1D X makes this one a bit strange with the current line of camera bodies.

Patent Publication No. 2012-47869

• 2012.3.8 Release Date
• 2010.8.25 filing date

Example 1

• -83.98mm focal length
• Expansion rate β = 1.996
• Lens Construction 5 group nine

Example 3

• -41.91mm focal length
• Expansion rate β = 2.779
• Lens Construction 5 group nine

Canon's patent

• Rear converter is to increase the focal length, F number, the residual aberration
• When doubled, twice the lateral aberration, longitudinal aberration is 4 times greater rate of expansion, because the F-number is also double, longitudinal aberration is twice per depth of focus
• Rear converter configuration consisting of three groups of positive and negative positive
• Reduce the aberration of the rear converter itself

Source: [EG]

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