Sidling or camera positioning errors may be in a direction to narrow or to increase the space available for overlap. When narrowed, the dark edge generally shows as in some underwater sequences; (bottom panel of Fig. 8) when increased it sometimes happens that the blend line is improved by removal of a camera vignette as in the AB side of some of the closing scenes of the picture where the rigging of the ship is considerably displaced because of some camera error, yet the blend is excellent.

    Another condition which needs rectification is better coincidence in positioning of the overlap area from camera to camera. The Fig. 9 shows how differently the overlap positions fall in Cameras #1 and #2 towards the close of the shooting schedule. Discrepancies are obviously a major proportion of the area available for overlap and imposed generally impossible limitations on printer operation especially since each printer step must be used for two different camera focus positions. In many cases, it is obvious that the feather cannot be positioned to fall completely within the clear overlap area and one side or other of the blend line is not properly feathered. The appearance of the matchline then looks like the center panels of Fig. 8, but only one bad edge shows or one edge is much worse than the other. These difficulties lead to specifying in Printer #2 a greater number of feather-position steps and independent operation of the AB and BC feather controls.

    When the facts are considered that these final alignment checks do not coincide with initial camera checks and that even with great care intermediate checks have shown severe tracking and coincidence errors, the need for designing better inherent stability into the camera lens mounts is at once apparent. The experience with the old alignment equipment has also indicated the need for improvement here also, a need which has been anticipated but of course must yet be proved in practice.


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