Your 24-135mm is a good lens man. use it. if you wanta get a zoom, try the minolta 75-300mm, cheap n not bad. more cash then try the 100-300mm zoom. make sure they are the D type lens if your camera hv the function. shooting in low light? you are gona need something faster, sigma 100-300 F4 (around $1550) not cheap or tokina 100-300mm F4 which is cheaper without the D function if you dont use flash. The tamron 28-300mm is not a bad lens but at F6.3,is a bit slow for some to use. Look around first, dont rush into buying. To me minolta 75-300mm is good enough, can save alot money by getting one. HAPPY HUNTING FOR YOUR NEW LENS.