[JOBY]

用一枝既18-200既好..定係 用兩枝分別係18-55和50-200既好？
邊一種出黎既相會比較好d？

[Obi-Wan]

In terms of lens design, a zoom with a larger zoom ratio requires more lens elements which results in more optical defects such as flare, CA etc.

So in terms of photo quality 18-55 + 50-200 are definitely better than 18-200 from the same brand.

Of course Nikon 18-200VR is much better than SXXXX $1500 twins lens 18-50+50-200 lah.

[JOBY]

it means that s SXXXX twins lens 18-50+50-200 must better than SXXXX 18-200 single lens?

[Obi-Wan]

JOBY, you wrote:

"it means that s SXXXX twins lens 18-50+50-200 must better than SXXXX 18-200 single lens? "

I don't have the twin lens, but I have the 18-300 SIGMA, the photo quality is so-so, but a good travel lens. I use it mainly for travel because it is very light.

Some of my friends have 18-50, they said the quality is also so-so

My conclusion: If u have $ buy 18-200, which can be easily resell;
if u don't have $, just keep your kit lens 18-50, 18-55 or 18-70 depends on you DSLR brand.
If u want a cheap cheap telephoto, the Sigma 70-300 APO or non-APO is a good choice, 2nd hand from $700 to $1000