QUOTE(Anly @ Oct 5 2010, 02:01 PM)
thanks~
if SAL18-250 compare with SAL55200, issit same IQ and CA ? or which one better? but SAL55-200 is much more cheaper than SAL18250,since i got 18-55mm lens already..

You cannot compare it like that. The two lenses are built for different crowds.
For sure the 55-200mm will beat the heck out of the 18-250 in the same ranges both in terms of IQ and aperture ratings but the 55-200mm is specifically a tele lens. You cannot leave the 55-200mm attached to your camera and go out with just that one lens. You will probably miss quite a number of shots if you do. (Landscapes and groups come instantly to mind.)
The 18-250mm however is designed to let you attach that one lens and go out and you'll still be able to shoot most of anything. The price you have to pay for that convenience is to sacrifice a little in terms of IQ and aperture rating.
For a person to cover the range from 18-250, he/she will have to bring at least 2 lenses if they do not want to use a superzoom. If he/she has only one camera body then he/she will need to swap lenses to get to use the different focal range.
Imagine that while out for a little stroll during your vacation, you see a new species of bird never seen before in this world. It's about to take off and go into the woods where no one will probably see it ever again. Standing where you are you can get a decent pic of the bird at 200mm focal length.
If you had the 18-250mm attached on your cam you could zoom all the way and get a decent shot.
If you had the 55-200mm but it's not currently attached to your cam, you would probably have lost the bird in the time it took for you to change lenses. If you have had the 55-200mm attached, you would have probably gotten a better pic of the bird in terms of IQ and exposure compared to the 18-250mm but that's a big IF.
That's the difference between the 2 lenses.