I purchased a used Tamron AF 18-200 F/3.5-6.3 lens for my D80 camera. Going in, I knew it was slower than the Nikon 18-200, and no vibration reduction. I've been using it a lot and I've captured some nice shots with it... especially at close to mid range. At 200mm and waning daylight it gets challenging for me to get good exposure and many photos are dark or blurry. I contribute this to slow shutter speed shooting in Program mode, and no tripod. I'm still an amature photographer but enjoy the hobby. I take my camera with me almost always when traveling. We hope to vacation in the Yellowstone this Summer. My lenses include the Tamron 18-200, Nikon 18-55 kit lens, Nikon 70-300 VR , Nikon 50mm 2.8 . I have almost enough money saved for a new Nikon 18-200 VR , since used ones bring almost new price on Ebay. Before I spend $700 for this lens, I'd like to hear opinions whether I'll notice the Nikon lens being faster at 200mm. Perhaps I need to practice technique, such as shoot in A or S priority instead of P mode ? Perhaps I should get used to shooting at higher ISO levels, such as 400-800 ? Thanks in advance for your help.