Optical Printers
Intermittent or Step
Optical Printers
Optical printing is a technique where the original and the raw stock films are not in contact with each other, but are separated by a lens system.
The image of the original is focused on to the raw stock film printing aperture by a lens system between the two heads. In essence, an optical printer can be regarded as a projector mechanism projecting an image of the original onto the print film, which is transported, by a camera mechanism. In some optical printers, it is easy to see the two separate parts, which are often called the "projector" and the "camera" mechanisms.
An optical printer is shown schematically in the illustration
Light from the source L is focused by a condenser lens C on to the objective lens OB. The original image OR is focused on to the raw stock by the objective lens OB.
The shutter S interrupts the light beam each time the two films move forward one frame. The original and raw stock are moved in opposite directions by the link claws J and K. O and R are the usual feed sprockets and 01 and R1 the hold-back sprockets.
A printer designed on this principle makes it possible to produce prints of equal size (1:1) and of a different size from the original, simply by altering the distance between the lens and the camera mechanism and focusing by adjusting the projector/lens distance.
Early optical printers were designed to make a print of exactly the same size as the negative [i.e. 1:1]. However, within a few years of the new century optical printers were able to make a larger or smaller print to accommodate changes of gauge and format and were often used to make selective enlargements to crop out unwanted detail, for example. A good example is to be found in the British Pathe collection where there are two versions of a short film using trick photography [double exposure in the camera] made about 1905. One is from the original negative at 1:1, the other is considerably enlarged to concentrate on the action and cut out the background, to improve the dramatic effect.
By the late 1930's the optical printer was widely used to reduction print, that is to make, for example, duplicate negatives or prints on 16mm from 35mm originals. In the 1960’s, optical printers began to be used extensively to blow up, for example to make 35mm prints from 16mm originals.
Some of the optical printers made were restricted in their ability to alter formats and magnifications, but those that were mounted on and "optical bench" that could move their various parts independently are extremely flexible and can "do anything". This type of printer offers several advantages, but also some disadvantages.
Advantages are:
- the possibility of setting the claw stroke for the original film differently from that for the raw stock, allowing badly shrunken originals to be handled.
- the possibility of small reductions or enlargements of the original image to make minor adjustments of magnification.
- the possibility of reframing horizontally and vertically.
- the possibility of copying films with a high degree of damage, because the original is in a separate gate to that containing the raw stock.
Disadvantages are:
- increasing contrast.
- increasing the apparent graininess of the final image.
- reveals more dirt, dust and scratches on the original.
- difficult to copy the informative marks on the margins of the original.
- possible introduction of a certain amount of flare.
Some of the older optical printers do suffer from quite serious flare. This is the scattering of light within the lens and mechanism that finally falls on the film as non-image forming exposure reducing the contrast. The increases in contrast and the increases in apparent graininess are largely due to poor lens design and modern optical printers have overcome most or all of these objections.
This type of printer is very suitable for archival use, especially when equipped for wet printing. Although many manufacturers made optical printers, only the best and the most flexible are suitable for archive use.
However just one of these printers can carry out all the operations required, and suffer principally from the shortcoming that they are generally, with the exception of the Debrie TAI, rather slow. Other examples are from Oxberry [USA], Neilson-Hordell [UK], Seiki-BHP [USA/Japan], and Acme [USA]
As with optical step printers the original and the raw stock films are not in contact with each other, but run continuously and synchronously at a constant speed in an opposite direction.
The figure shows the principle on which the Sigma continuous optical wet printer was built.
The constant light beam from the source L projects the original image OR, reflected by two mirrors or prisms A and B and passing through the light change system LS and the objective OB, on the raw stock film RS. This type of printer has the same disadvantages and advantages as the optical step printer when specially equipped.
For archive work the Sigma printer made solely for the National Film and Television Archive laboratory at Berkhamsted UK, is the only example of this printing principle used for archive printing. However, other printers exist and used to exist using this principle. The largest were those made in the 1970's to print from 16mm or 35mm negatives onto 2, 4 or even 8 rows of Super 8 on 16mm, 35mm or 70mm film, printing all the rows simultaneously via a beam splitter optical system. Most of the product was either educational films or adult movies, neither of which seems to be collected in archives much yet!
Whichever type of printing machine (step or continuous, contact or optical)
is used, the optical sound track printing is always carried out on a separate
rotary contact gate. This is not a problem on a rotary contact printer as a
second gate can be placed after the image gate and at this point the separate
sound negative replaces the image negative.
On intermittent printers, sound gates [often called sound heads] are positioned
some distance from the image gate after the loop by which time the film
movement is continuous and smooth. The sound gate is a narrow slot no wider
than the width of the sound track.
Many optical printers have no sound heads and tracking, as the process of printing an optical sound track onto a print has to be done on a separate printer as a separate printing run. Rotary contact printers are mostly used for this. The biggest problem with this procedure is the synchronising of the picture image on one printer with the sound on another. This procedure was commonplace in the early days of optical sound and in the early 1930’s; several printers were available on the market simply to print the sound tracks after the picture had been exposed. Only later were printers fitted with sound heads in the same film path.