I have the SIgma 150-500 and bought it using bill me later. Every paycheck I put money towards it. It was cheaper 3 years ago and cost me $900.00 There are some used ones on the sell it forum. I had to send it in last week for a check up and went to my friends backyard for birds. She is learning and I had to give her some pointers of which I had learned here.I had to use the 70-300 VR and it did a great job even though I had to crop a whole lot. I have just recently been happy with my shots because I practice alot. I shoot hundreds just to see what angle of the bird is the best. Its hard to get them to look in the direction you want them too. I start out by getting out of the car slowly and I close the door real slow and take a shot. I then take small steps to get closer and sometimes I have to stop because they look like they are going to bolt. Sometimes they just stare at me and I could swear they are thinking "look at that crazy woman". I am bad at flight and am going to try next week at Lock anDam 14. You should go to the wildlife forum. They are a big help. I was in Florida last lmonth and the birds pratically posed for me. I used the 70-300 VR for a long time until I got the 150-500 and when I got the bird in perfect focus I was able to crop to get that perfect picture. I showed you a while back the eagle and that was cropped with that lens.Check out the other forum. The pictures that are posted there make me droll.