A few millimeters here and there can make a big difference: Tamron’s newly announced 50-300mm F/4.5-6.3 Di III VC VXD zoom lens for full-frame Sony mirrorless cameras.goes a bit wider than traditional 70-300mm lenses without sacrificing any light—it keeps the same f/4.5-6.3 aperture without increasing much in size, notes DIY …