Tamron is no stranger to producing lenses with unconventional focal ranges. There's the 35-150mm f/2-2.8 Di III VXD, 20-40mm f/2.8 Di III VXD, 17-70mm f/2.8 Di III-A VC RXD, and most recently, the 35-100mm f/2.8 Di III VXD. All are excellent lenses though, with their non-standard focal lengths bringing benefits like additional shot versatility and better overall portability.
Now it seems Tamron could be planning another unique lens, this time with a 50-130mm focal range. The tip-off comes from a recent release of a Tamron patent application, which mentions an extremely precise focal length of "51.5100-130.9425". 'F value' is quoted as 2.8840, so presumably the design would feature a constant f/2.8 maximum aperture.
Judging by the patent diagrams, the design features 17 lens elements, arranged in 7 groups. Three separate diagrams show the position of the elements with the lens set to its shortest, medium and longest focal lengths, and it's clear from these that focussing would be internal, unlike Tamron's 35-100mm lens where the barrel extends as you increase focal length.
As this is only a patent application, there is absolutely no guarantee Tamron will actually manufacture such a lens, let alone when we might get our hands on one. However, if it did choose to put a 50-130mm lens into production, the focal range could be very handy for applications like portraiture. At 50mm you'd have the option to shoot full-length images, or even small group shots. 130mm would be suitable for tight close-ups, and there's every option in between for other compositions. What's more, if the lens was to also have a reasonably high magnification factor, it could also double as a useful tool for macro photography.
