Archives for October 21, 2008

Canon EF-S 17-85mm IS USM vs 18-200mm IS

Canon 18-200mm IS is the new general purpose lens released in Fall 2008 with Canon 50D. This lens is ideal for vacation due to its versatile focal length. 
Canon also have 17-85mm IS USM f/4-5.6. Both are considered in the same class as 18-200mm. But which is better? 
17-85mm auto focus operation is faster and quieter. This lens is also around $175 cheaper. But 18-200mm has 125mm focal length advantage. This allows 18-200 mm users to shoot nature such as birds, ducks etc. Also this lens could be used to shoot outdoor sport. The Image Stabilization of 18-200mm is 1-2 stops better than 17-85mm too.
Here are some observations about these two lenses:
  • Shooting at 17mm wide open (largest aperture available) both of the lenses as similar sharpness. 18-200mm is sharper in the center but worse in the corner. 
  • Shooting at 24mm-f/4, 18-200mm is sharper in the center. 
  • Shooting at 50mm f/5-6, 18-200mm is significantly sharper in the center
  • Shooting at 80mm and 85mm f/5.6, 18-200 has worse corner sharpness.
  • Shooting at 135mm f/5.6, 18-200mm has very bad corner sharpness.
  • Shooting at 200mm f/5.6, 18-200mm is sharp at f/8 but suffers from high chromatic aberration or color fringing in high contrast areas.
In conclusion
Overall Canon EF 18-200mm is sharper in the center across the focal length but worse in the corner. At telephoto end, from 150-200mm, this lens suffers dramatic color fringing.
Both lenses are not perfect, but they are good enough for casual use. Mechanically, 17-85mm has a better AF operation but 18-200 has better IS. 18-200mm has also longer focal length.
So does investing $175 more for 18-200mm worth it? it depends on your needs. Are you planning to use the lens for outdoor sport / nature? If yes than you will need 18-200mm otherwise, 17-85mm might serve you well. 
Other alternative for general purpose lens in the same class (consumer class) are 28-135mm IS USM.