Analysis of Sharpness 18-200mm versus 18-70mm
Prepared 2006-01-09 (146/47187) by Bill Claff

I haven't seen any evidence of sharpness problems with my new 18-200mm DX but thought I'd do a quick analysis for "completeness".

Caveat: These tests were performed at relatively short distances and both of these lenses are probably optimized for further subject distances.
Never-the-less, I think it's a valid comparison.

Like the distortion test, the subject to sensor distance was controlled so that magnification was held constant across all images.

I tested at each marked focal length.
I tested at f/5.6 and at f/11.
I test with and without VR.
(On a tripod I didn't expect any real difference.)

Here is a chart that summarizes the results:


I apologize if it's a little confused since I may have put too much on one chart.
If you focus on the green (18-70mm), you'll see that it's not clearly better or worse than the red/magenta (18-200mm) except that the 18-70mm seems to outperform the 18-200mm at 70mm.
In some ways it looks like the 18-70mm "falls down" at 50mm given the "kink" in the green lines.
(It also looks like on a tripod the VR hurts sharpness lightly since the red lines are generally higher than the magenta lines.)

For your additional amusement here are 100% crops from the test images:


The decoder ring is:
f/5.6 above f/11
18-200mm without VR above 18-70mm above 18-200mm with VR
18mm, 24mm, 35mm, 50mm, 70mm, 135mm, and 200mm left to right.