Ive just got the 70-300vr, which i am very pleased with. Its a nice lens. Im quite new to all this and I was hoping 300mm would give me some reasonable wildlife shots but even at 300mm I cant get close enough really. Only by zooming after thus losing sharpness. Whats the minimum realistically for wildlife/birds?? Also if i used a teleconverter would the VR still function ok?