I have read a number of articles from professional photographers that claim that teleconverters are a waste of money and to avoid their use. They seem like a handy tool to have around for certain prime lenses - particularly macro work or some portrait work from a distance. Any thoughts here? I think a reasonably good quality 1.7X could be had for a couple of hundred dollars. Is that about right? I'd just like some input from actual users. Thanks in advance.