Would a Teleconverter help?

You've got a good camera and lens combination already in that K-5 and 55-300. Was I you I'd do three things:

1. Crop a lot. You'd be surprised at the sharp and clear results you can get with that combination if the photograph is well lighted and the exposure is dead on.

2. Buy yourself a hunter's blind (about $75 at Cabela's) and find an old aluminum lawn chair. Set it up close to a tree that is a favorite of eagles or whatever you're looking for. Have patience. Listen to music on your iPod. Sit still. It may take a couple of hours but you likely will get something.

3. Use Lightroom to adjust, sharpen and denoise your cropped photographs.

Works for me.

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http://www.hkisorphoto.blogspot.com