Looks like you're off to a good start! At that focal length, sharpness is more about the tripod and head than the lens, and a bigger tripod and head will let you use a slower or medium-speed film, which will improve things as well. When I was doing a lot of bird photography, usually with a Canon FD 600/4.5 + 1.4x-A, I was generally using Provia 100F, shooting one stop from wide open usually, with the fastest shutter speed I could get. You might also experiment with a static subject and compare using a cable release vs. keeping your hand on the camera or resting your hand on the lens to dampen vibrations. Some people use a sandbag on the camera or the lens to reduce vibration as well. The best approach varies with the camera, tripod, and head, so you can learn a lot by testing with film and taking notes.
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