Asobinet spotted two brand new Tamron patents that disclose two unique telephoto zoom lenses with Fresnel design:
- Tamron 400-1000mm f/10-11.5
- Tamron 250-700mm f/6.5-13
The Fresnel design allows those lenses to be more compact than “classic” lenses. The downside is that you loose a bit of Image Quality and Speed. An example of such a lens is the Nikon AF-S NIKKOR 300mm f/4E PF ED VR Lens.
Considering the crazy focal lenght I think this is a wise choice from Tamron to use that desing to keep them more compact.