John Fares sent in a question via the Ask a Question page in which he essentially asked why some photographers recommend buying the expensive high-end lenses when there are cheaper lenses of the same focal length available. What's the difference between cheap lenses and expensive lenses? You can read the full question at the end of this article.
First of all, I would NOT recommend that a beginner buy a high-end lens. Why? Because you probably won't see any significant improvement in your photos. Think of lenses as a bottleneck. If the photo is otherwise compelling, the photographer has the skill to shoot with proper technique, and the photographer is skilled in post-processing, then the lens can add to the sharpness, color, and contrast of the photo. HOWEVER, even the sharpest and best-built lens will produce blurry photos in the hands of an amateur.
But if you feel like you are skilled enough to take advantage of a pro lens, here is a list of some of the advantages you'll seen in the professional grade lenses, and why they are different than the cheap kit lenses.
Benefit of Professional Lenses #1: Maximum Aperture. This is probably the most important benefit of an expensive lens. Most low-end lenses have max apertures of f/5.6 at the long end of the lens; however, professional lenses often have max apertures of f/2.8 or even lower. The large apertures offered by professional lenses aides in creating shallow depth of field and light-gathering.
Benefit of Professional Lenses #2: Constant Aperture. Most cheap lenses change the max aperture as you zoom out. For example, the popular Canon 75-300mm lens can achieve an aperture of f/4 at 75mm, but when you zoom out to 300mm, the lens can only achieve an aperture of f/5.6. On many professional lenses, the maximum aperture available on a lens is constant throughout the focal length range. For example, the 70-200mm lens by both Canon and Nikon can achieve an aperture of f/2.8 at the 70mm or 200mm ends.
Benefit of Professional Lenses #3: Focus Motor. More expensive lenses use a silent wave motor, which produces faster and quieter focusing.
Benefit of Professional Lenses #4: Weather Sealing. While all lenses have a certain amount of weather sealing, high-end lenses have loads of it. This makes the lens last much longer without problems. I have rarely seen a kit lens or cheap telephoto lens that doesn't have dust (or even mold…) inside the lens after a year or two of use. This happens much more rarely in professional lenses as long as they are taken care of.
Benefit of Professional Lenses #5: Sharpness. Kind of self-explanatory, but pro lenses are almost always sharper. However, this won't make a bit of difference if you don't use proper technique.
Benefit of Professional Lenses #6: Internal Focus. On cheaper lenses, the physical length of the lens extends as you zoom in. On many professional lenses, the lens focuses without changing the length of the lens. The only reason this matters is when using filters. This creates problems when using certain types of filters.
Benefit of Professional Lenses #7: Contrast. Professional lenses often produce significantly more saturated colors than cheaper lenses.
Benefit of Professional Lenses #8: Chromatic Aberration. Professional lenses produce less-noticeable fringing around edges. This really isn't a big deal unless you're printing or displaying photos large.
Benefit of Professional Lenses #9: Color. The difference in color reproduction is slight, but professional lenses do a bit better.
John's full question: