PASADENA, Calif. (AP) - NASA's Deep Impact spacecraft is on course for a July 4 encounter with comet Tempel 1 but mission officials are trying to determine why a telescope that will function as its main science instrument has not reached proper focus, the space agency said Friday. Officials nonetheless expressed confidence that the mission will not be affected by the problem. Deep Impact carries an "impactor" that will be released to collide with the comet, possibly creating a stadium-size gouge while the spacecraft's instruments collect data on the material that is hurled off. The craft was launched on Jan....