Canon 2.8X Teleconverter Patent surfaced today, but the bad news it if you attach 400mm F2.8 lens with 2.8x Extender, Canon EOS 1DX/5D3 DSLR AF will not work, So after this patent we may see a Firmware Update Soon to fix 1DX and 5D3 F8 issue.
EOS1D4 (APS-H) + 400mm F2.8 + Extender 2x = 1040mm (35mm equiv.) F5.6
EOS1DX (Full-size) + 400mm F2.8 + Extender 2.8x = 1120mm F8
Patent details (translated by google)
Self-interpretation and summary, Patent Document
- 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
via – egami
