It seems that zoom lenses of all brands and systems are either slow and small, but not so good image quality; or they are fast and big, with very good image quality. Why can't there be slow and small lenses with "pro" grade image quality? Is there really no market for such lenses? For example, the 40-150 f4-5.6 costs $150, is 190 grams and 83mm long. The image quality is not bad but not great either. The 40-150 f2.8 costs $1500, more than 4 times the weight and twice as long, but superb image quality. Would you buy a 40-150 f4-5.6 that weighs 300 grams, is 90mm long, weather-sealed, costs $1000, and has the same/better image quality than the f2.8 version at the same settings?