People often wonder which lens to buy. There is no quick nor easy answer to that. It's like asking which car you ought to buy. It depends – on your needs, your budget, your skills, your style. Before you buy anything however, it is important to know the difference – in practical terms – between 35mm and 200mm on a camera lens. A chart like this one is an excellent visual. More here:
You will see right off that the small the focal length, the wider the angle and the more panoramic the view you capture. Zooming in enlarges a focal point in the distance at the expense of the peripheral images.
In general, if you are traveling or want to have the story telling capacity of a wide image (ie you wish you photograph groups or capture the entire room in your house) use a smaller focal length such as 15-50mm.
Even at 50mm it is maddeningly impossible to photograph an entire building if you are on the same block. I brought a 55-200 lens to Paris two years ago. Big mistake. We walked 3 blocks from the Eiffel Tower and I still couldn't get the whole thing in the screen. My husband's cell phone managed just fine. : p Live and learn.
Portraits are better done at 50-200mm. It flattens out the features nicely and avoids the lens distortion common to close-in shots with a wide angle lens.
Starry Sky Journal 