Photography in the '50s was quite capable of resolving not only this type of action but MUCH faster actions (like bullets). The only photographic element that would deliver a curved line is the spherical distoration common in wide angle lenses but that would distort the whole field. Note that there is nothing that has the curvature but the shaft and that includes the shaft in the same area of the photo as undistorted items. If this were an effect of slow shutter speed required due to slower films, lenses...the moving objects would be blurred. The shaft is blurred but not to a degree that would allow it to have anything but the curved shape shown.
Then of course there are the comments by Jack and Gary.
The same effect (though less dramatic) is visible in photos in Dante Gerry Hogan and in the lead photo of John Daley in this months Golf Digest.
The degree of bend need not quickly compromise the integrity of the shaft. In fact long drive competitors have for a long time achieved shaft flex in the swing nearly as great as shown in the photo based on photos I've seen of them.
Seeing this led me to look at some other aspects of the dynamics of the downswing. Even in those pro swing that do not have the dramatic upward bend of this photo, the shaft is at best straight at 6/100s. However apx 2 video frames before when the shaft is apx vertical it has a significant bow in the direction of the downswing (club head lagging). The fact that this bow disappears by '6/100s' is indicative of the same forces that would lead to the upward bow (club head passing) shown in the Nicklaus photo.
There are no photos/videos I've seen since starting this today that have a downward bow at '6/100s' or the frame after that would be an indication of the club being accelerated by a force from the trail hand which would produce IMHO a lag of the club head. The next occaision of clubhead lag is at impact (as would be expected).
