For the sake of saving my\e some typing, I'll refer to the 18-200mm lens as the 18 and the 55-200mm lens as the 55.

To get more consistent results, I tripod mounted the camera for all shots. For the bottom two, I adjusted the tripod height by 1.75" (the distance by which the 18@200 is longer than the 55@200) to maintain the same distance from the center of the object, so that the tip of the lens was exactly 43" away from the subject.


<b>18@55mm on top, 55@55 on bottom</b>
<img src="http://pictureposter.audiworld.com/8862/18_200_at_55mm_small.jpg" border="1">
<img src="http://pictureposter.audiworld.com/8862/55_200_at_55mm_small.jpg" border="1">

<b>18@135mm on top, 55@135 on bottom</b>
<img src="http://pictureposter.audiworld.com/8862/18_200_at_135mm_small.jpg" border="1">
<img src="http://pictureposter.audiworld.com/8862/55_200_at_135mm_small.jpg" border="1">


<b>18@200mm on top, 55@200 on bottom</b>
<img src="http://pictureposter.audiworld.com/8862/18_200_at_200mm_small.jpg" border="1">
<img src="http://pictureposter.audiworld.com/8862/55_200_at_200mm_small.jpg" border="1">


<b>18@200mm on top, 55@105 on bottom</b>
<img src="http://pictureposter.audiworld.com/8862/18_200_at_200mm_small.jpg" border="1">
<img src="http://pictureposter.audiworld.com/8862/55_200_at_105mm_small.jpg" border="1">


So I think it at this point it goes without saying that something's not right with the 18-200mm lens and I'm planning on sending it in to Nikon tomorrow. What I'm curious about is what could cause a 200mm lens at full zoom to act like a 105mm? A stuck element? Glass Nikon forgot to put in?

it is not uncommon for such zoom lenses to change focal length dramatically at various focusing distance. So it wouldn't be surprising that the 200mm rating represent the lens at infinity, and at close focusing distance it is significantly less.

18-200 at 200mm
<img src="http://pictureposter.audiworld.com/8862/18_200_at_200mm_ld1_small.jpg">

55-200 at 135mm
<img src="http://pictureposter.audiworld.com/8862/55_200_at_135mm_ld2_small.jpg">

55-200 at 200mm
<img src="http://pictureposter.audiworld.com/8862/55_200_at_200mm_ld1_small.jpg">

make sure to get some shots @ infinity

"...and will vary to some degree as the lens is focused at closer distances."<ul><li><a href="http://cameralabs.com/features/18200_issue/">http://cameralabs.com/features/18200_issue/</a</li></ul>