Third, everyone should be convinced by this time that neither the camera nor the projector should have any aperture or vignetting encroaching on the space allotted for the printer blend line. The effect are additive, and in the presence of an otherwise perfect blend, the spurious vignetting effects are plainly visible. There are numerous examples in the picture. In this case, the projector can be corrected readily and permanently. However, such effects in the camera are permanently recorded on the negative, and can rarely be corrected in the printer which must never be considered a corrective device. An obvious corollary is that the camera overlap at its narrowest must be wider than the printer vignette for all focus and aperture settings.Fig. 7. This is of particular importance at the closest focus distance where the camera overlap is the least, and at the widest lens aperture where camera vignetting extends into the overlap area and is further aggravated by distortion. These effects are shown in Fig. 8.

    Since the printer vignette width is already somewhat too narrow for good control, it is necessary for the cameras to be readjusted to provide a greater overlap free of camera vignetting if improvement is to be made in matchlines. There is no alternative. The requirement is fundamental.

    True, an increase in overlap simultaneously increases parallax. However, this picture demonstrates that the presence of a perfect blend line, mismatching due to parallax is difficult to find particularly with skillful camerawork. In fact, many of the most obvious mismatch errors have not been due to parallax but to gross camera positioning errors.