I just got back from a weekend trip, and had some problems with my new setup I lost out on a lot of good photo opportunities because my camera kept flashing "F --" on the top LCD screen. Sometimes if i turned the camera off and then back on it would fix it, but other times it wouldn't. In addition to that, i was trying to take some low light photos and it never would quite focus (was indoors at an aquarium). I took my 67mm Tifen UV filter off, and it seems to help a bit, but not much. It was also having some problems focusing on objects far off in the distance (was in Gatlinburg, and wanted to take some photos of the mountains). I have only had this setup for a couple weeks, and it seemed to work fine at first. After much frustration, i finally threw my Nikkor 50mm f/1.8 on there, and it seemed to perform fine. Do you think there is a defect with my Tamron lens? i have heard of some AF problems with non-nikon lenses, but this was a little extreme. If there is genuinely a problem with it, i want to figure it out now so i can return it. Its really frustrating to pay $400 for a lens, only to have it not act right. I guess i should ad that both the D90 and the Tamron lens were puchased new about 2 weeks ago.