It looks like Tamron may be entering the world of fast supertelephoto lenses. Three different optical formulas have appeared in the same patent application from Tamron.
Embodiment 1: 300mm F/2.8
- Focal length: 304.799 mm
- F No.: 2.8
- ω: 3.997
- Image height: 21.64 mm
- Back focus: 70.1919 mm
- Lens length: 298.38 mm
Embodiment 2: 400mm F/4
- Focal length: 396.296 mm
- F No.: 4.0
- ω: 2.963
- Image height: 21.64 mm
- Back focus: 102.3549 mm
- Lens length: 332.36 mm
Embodiment 3: 500mm F/4
- Focal length: 485.045 mm
- F No.: 4.001
- ω: 2.530
- Image height: 21.64 mm
- Back focus: 125.2621 mm
- Lens length: 420.001 mm
I think a 400mm f/4 is a lens missing from everyone's lineup. Apologies to the Canon 400mm f/4 DO IS II, but I think a non-DO version would likely cost less and could give equal or better performance at the expense of reduced size and weight. Maybe there's an engineering reason that I am unaware of as to why a non-DO 400mm f/4 doesn't exist for Canon's EF mount.
