I have used a lot of professional lenses, being a professional sports photographer in a previous life and I have to say the standard 70-200mm f/2.8 lens is the workhorse for the pro sports photographer, wildlife shooter, or even landscape photographers looking to isolate subject. The Leica 90-280mm APO-Vario-Elmarit-SL f/2.8-4 with its 90-280mm focal length is an incredible lens to use in the real world, and having that extra reach towards the 300mm end really comes in handy.
While I use a lot of prime lenses in my work, the one zoom lens I use time and time again is the "Trinity" 70-200mm, and having used the Leica 90-280mm APO-Vario-Elmarit-SL f/2.8-4, it is for certain that this lens is targeted at pro photographers looking for that "Trinity" workhorse lens when switching from other systems to Leica.
