Size and Weight Comparison
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Nikon 28-300mm f3.5-5.6G ED VR weighs 800g, 113% (910g) lighter than the Leica Elmarit-SL 90-280 mm F2.8-4's weight of 1710g.
Lens Mounts
Both Leica Elmarit-SL 90-280 mm F2.8-4 has the Leica SL lens mount whereas the Nikon 28-300mm f3.5-5.6G ED VR has the Nikon F (FX) lens mount. Some of the latest released cameras that are compatible with these mounts are Sigma fp L, Leica SL2-S and Panasonic S5 for the Leica SL Mount and Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount.
Focal Range
Leica Elmarit-SL 90-280 mm F2.8-4 has a focal range of 90-280mm and 3.1X zoom ratio . Nikon 28-300mm f3.5-5.6G ED VR has a focal range of 28-300mm and 10.7X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 42 - 450mm.