Hi Wildman,
I'm pretty sure an 18-200mm f/2.8 doesn't exist, and may never will. Let's just say some 3rd party lens-maker decided to try it. Two questions; How would you pay for it, and how would you lift it?
Even a constant f/4.0 zoom with the same focal range probably won't be coming to a store near you, anytime soon. Too many compromises in construction, IQ, size and price.
Suppose you sat in the same chair, with the following lenses (bear with me here);
A 24m f/2.8 (I have a Miranda M/F PK-A that's sharp as a tack, there are others), your 35mm f2.4, a fast fifty and an 85mm f/1.4 (or f/1.8, f/2.0, you get the idea).
Now, with the 24mm, you take a bunch of group shots. Change to the 35mm, take more. Same with the fifty, then "head" shots with the 85mm.
So, you'll get pretty much the same selection of shots, all will be sharper than any zoom going, your slowest lens is f/2.8, ISO is greatly reduced, and/or faster shutter speeds.
But, you do have to change lenses.
You can substitute an UWA f/1.4 (or so) if you really want to get every wall in the room. Maybe a 100mm f/2.8 or even a 135mm f/2.8. Maybe 2 bodies.
More work? Yes. Better results? Yes.
JMO,
Ron
Last edited by rbefly; 11-29-2012 at 05:38 AM.