I use which ever lens is appropriate for the composition. I recently photographed a scene ( Villa Vizcaya, Miami,Fl) across the bay from a beach at least a half a mile or more away with my Hasselblad 350mm (40 year old) lens plus the Mutar 2x. Amazing detail and sharpness even recording the parking lot lights on a pole top in front of a tree in the background. I was pleasantly surprised with the result since it wasn't an intended shot just seeing what might come out with that combination.

http://www.jeffreyglasser.com/