Seeking a lens to supplement 18-55mm kit lens for my Nikon d3100. Am interested in portraits - both people and pets - and nature photography. The Sigma 70-300 f4-5.6 with AF, Zoom and Macro looks like a nice contender and the price is very reasonable. My hands have a slight tremor so a tripod might be helpful although I'm not very familiar with them. Would be best - I think - to find one that is not too heavy, easy to assemble and user-friendly. Thank you for reading this; all ideas/recommendations are appreciated.