DX Lenses

• Both the Sigma 18-200 mm and Nikon 18-200 mm are DX lenses, meaning they are designed primarily for the cropped APS-C sensor found on Nikon cameras like the D90, D80, D300, D200, D5000, and D3000. Both lenses can be used on the full frame Nikon cameras like the D700 and D3, but the camera will crop the megapixels of the sensor from 12 to five.
  
  

Focal Length/Aperture

• The Nikon 18-200 mm and Sigma 18-200 mm are 11x optical zooms, covering the 35 mm equivalent of 27-300 mm. Both have a variable maximum aperture, but the Nikon's is better for low light. The maxium aperture on the Nikon is f3.5 to f5.6; on the Sigma, the maximum aperture is f3.5 to f6.3. The minimum aperture on both is f22.
  
  

Image Stabilization

• The Nikon 18-200 mm is a VR (vibration reduction) lens. It is image-stabilized and can shoot handheld four full stops more than a similar lens without image stabilization. The Sigma is not image-stabilized.
  
  

Lens Construction

• The Sigmas has 15 lens elements in 13 groups, including two SLD (special low dispersion) lenses and two aspherical lens elements. The Nikon has 16 lens elements in 12 groups, with two ED (extra-low dispersion) lenses and three aspherical lens elements. Both have an internal focusing motor.
  
  

Focusing Distance/Angle of View

• The minimum focusing distance for the Sigma is 17.7 inches, and the angle of view is 76.5 degrees to 8.1 degrees. The minimum focusing distance for the Nikon is 18 inches, and the angle of view is 76 degrees to 8 degrees.
  
  

Filter Thread

• The Sigma lens takes 62 mm filters. The Nikon lens takes 72 mm filters.
  
  

Size/Weight

• Nikon is 3 inches wide by 3.8 inches long, and weighs 560 grams (19.75 ounces). The Sigma measures 2.8 inches wide by 3 inches long, and weighs 395 grams (13.93 ounces).