I have a Pentax K10D with a 28mm lens that will not focus on distant objects. Will an extension tube solve this problem? I do not care about autofocus. Is one tube better than another for manual operation?
will not focus an distant objects. Will an extension tube solve this problem?
No, extension tubes allow focusing closer but at the same time prevent focusing to infinity. It shifts your focus range down.
It sounds like your lens needs readjustment or repair. Start with a close inspection: any loose parts, rattling, buildup of grease? Does the focusing ring turn smoothly and to a dry stop?