Hole spacing

With hole spacing the measure of the general distance between two adjacent holes in a row of holes which is in the film art film perforation (Filmlochung), respectively. The hole spacing can in particular differ from the general one, which corresponds to the procedure for perforating (punching holes). Motion picture film is mainly perforated intermittently, i.e. deposited in groups of holes. With normal film , a group of holes comprises four pairs of holes or eight individual holes, with wide film 65 mm and 70 mm there are five pairs of holes.

It is obvious that the hole spacing within a hole group can be maintained more precisely than from group to group. However, so-called hole group marks are out of use. These are short lines of ink between the groups of holes, made by the perforating machine on the edge of the film or on the hole bar. When the raw film is clamped into the camera, the technician can ensure that the respective group of holes is detected by the positioning elements, such as locking pins, which are located directly at the picture window . The distance error between the groups of holes is on average 1.6 times larger than the error within one.

The image chain is closed if this link between the image and hole group is maintained when copying and projecting.

Narrow film 16 is usually perforated with groups of three or four holes.

Hole spacing is not to be confused with positioning spacing . See also the nomenclature of the closest film technology

Why two dimensions for the hole spacing?

For professional film formats, there is perforated material with full hole spacing and perforated material for short. The reason for this is economic pressure, because with the so-called ring gear or slot copier you can copy faster than with step copier.

The starting material runs on the outside layer over a ring gear of a film foot circumference. The raw film lies on top of the inside layer. So that both strips can be moved as much as one body, there must be a difference in the distance between the holes. Celluloid film is subject to a shrinkage of around 2 ‰ on drying after development. Together with the slight shrinkage during storage, this results in a shortening of about 3 ‰, which corresponds to the desired difference. Cellulose triacetate and polyester films shrink much less or not at all. Therefore, with the introduction of these security films, a new dimension for the hole spacing has become necessary. For normal film there are the indications 1870 and 1866, which means 0.1870 "and 0.1866" (inches), respectively 4.750 and 4.740 millimeters. Also 16 mm film is available with different hole spacings: 0.3000 "and .2994" or 7,620 and 7,605 millimeters.