Quote Originally Posted by Rubar View Post
Hi again!
To be honest, I did not expect so many replies. Thank you all for your input. As I see there are many different opinions and excitement, but still no clear answer. At least I still don’t get it. I shoot different objects with Canon EOS 600D at about 100-300 meters (328-980 feet). With EF-S 18-200mm f/3.5-5.6 IS lens I get quite satisfying results for my purpose. Only thing I’m missing is a little extra zoom. While planning to get a new lens I consider getting a higher quality one.
By extra zoom, you mean longer focal length. That means you need a lens longer than your current max of 200mm. An EF 70-200mm L lens will give you better quality, but no more 'reach'. So, consider lenses like the 70-300mm f/4-5.6L IS, or the 100-400mm, the 300mm f/4L IS, or the 400mm f/5.6L. All of those will give you better quality, and a longer focal length (some more than others).

Bottom line, for you right now, only the number matters. You can get any lens, EF-S, EF, or L, but if you want more zoom than your current 18-200mm lens, you need a lens longer than 200mm. All of the diagrams you posted and the discussions that you referred to will only apply to you if/when you decide to get a full frame camera like a 5DII. At that point, a 200mm lens on that full frame camera will give you the same field of view as a 125mm on your current camera, so if you go FF, you may need longer lenses, too. But for now, don't worry about any of that.