Better yet, a series not only at 8ft, but at f8, and 1/8th of a second!

Or you can take a look and see if the camera was dropped, check for dents along the lens. A dented lens may not turn. If it looks ok you can try warming the camera up, let it sit on a window sill for a bit and try moving it. Sometimes the older grease will loosen with a bit of warmth. And if you are really feeling up to it, you can try a drop or two of naphtha along gap where the focusing ring is. This isn't the best way as you can have the liquid and whatever dirt and grease it carries get onto the lens elements or aperture blades.

Other obvious options is to send it out for a cla if it's an important camera to you, or you can try and strip it youself.