answer: Images are clean and crisp, and the autofocus is butter smooth
paragraph_question: question: Where is there a good contrast of colors?, context: After purchasing a Nikon D70S with the Sigma 18-200mm lens, I recently purchased a Nikon D200 and a Sigma 10-20mm ultra wide lens. This lens is one of the best I have ever used on any kind of camera. It not only has a good professional look and feel to it, but it works flawlessly with the smoothness of lenses in a much higher price range. Images are clean and crisp, and the autofocus is butter smooth. I paid a bit over $500 for mine and I doubt there is a nickels worth of difference, except in price, between the Sigma brand and a comparable lens bearing the Nikon name. This lens is a keeper for sure!! 
question: Where is there a good contrast of colors?
sentence: Images are clean and crisp, and the autofocus is butter smooth .
paragraph: After purchasing a Nikon D70S with the Sigma 18-200mm lens, I recently purchased a Nikon D200 and a Sigma 10-20mm ultra wide lens. This lens is one of the best I have ever used on any kind of camera. It not only has a good professional look and feel to it, but it works flawlessly with the smoothness of lenses in a much higher price range. Images are clean and crisp, and the autofocus is butter smooth. I paid a bit over $500 for mine and I doubt there is a nickels worth of difference, except in price, between the Sigma brand and a comparable lens bearing the Nikon name. This lens is a keeper for sure!! 
sentence_answer: <hl> Images are clean and crisp, and the autofocus is butter smooth <hl> .
paragraph_answer: After purchasing a Nikon D70S with the Sigma 18-200mm lens, I recently purchased a Nikon D200 and a Sigma 10-20mm ultra wide lens. This lens is one of the best I have ever used on any kind of camera. It not only has a good professional look and feel to it, but it works flawlessly with the smoothness of lenses in a much higher price range. <hl> Images are clean and crisp, and the autofocus is butter smooth <hl>. I paid a bit over $500 for mine and I doubt there is a nickels worth of difference, except in price, between the Sigma brand and a comparable lens bearing the Nikon name. This lens is a keeper for sure!! 
paragraph_sentence: After purchasing a Nikon D70S with the Sigma 18-200mm lens, I recently purchased a Nikon D200 and a Sigma 10-20mm ultra wide lens. This lens is one of the best I have ever used on any kind of camera. It not only has a good professional look and feel to it, but it works flawlessly with the smoothness of lenses in a much higher price range. <hl> Images are clean and crisp, and the autofocus is butter smooth . <hl> I paid a bit over $500 for mine and I doubt there is a nickels worth of difference, except in price, between the Sigma brand and a comparable lens bearing the Nikon name. This lens is a keeper for sure!!