I use a sony hdr hc7 to video long range shots while varmint hunting. A excellent tripod is a requirement. Also if you are going to use a doubler purchase one specifically for a hd camera as they use a better grade of glass.
One other thing to remember have fun. At 50+ yards there are not that many problems getting a good picture. I have videoed rock chucks at 800 yards that some times are as crisp and clear as a bell. Some times not so much. Wish I knew why
