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Cinematography page 4

 
In the British journal of photography on September 8th, 1871 an English doctor, Richard L Maddox, announced his method of spreading a warm solution of gelatin onto glass plates, the gelatin being mixed with cadmium bromide and silver nitrate. With this, a further step towards modern photography was taken; a light-sensitive emulsion could be coated on an independent support material.

By around 1883 further developments in emulsion chemistry had given the world an efficient dry photographic plate, made of glass, which could be prepared long in advance of the need to use it. This could be kept for a considerable time after exposure and before development and required less than a second's exposure in daylight.

By 1889, George Eastman was using a thin film of the plastic celluloid as a base material for the film for his latest amateur still camera. It was the introduction of this support medium, or base, that produced the last factor needed for a film that could be used practically by the inventors of motion picture equipment.

The early film bases were made of nitrocellulose. This produced a very transparent and flexible support. Unfortunately the material is also highly inflammable and somewhat dimensionally unstable. By 1920 a 'safety' base using cellulose acetate became available which is more stable, slow to ignite and burned at the same rate as paper. It is the instability of the nitrate base that is the main reason for the poor survival of early films. 

Today, many of the films from the early to mid 1900's are no longer viewable. Unfortunately, developers continued to use a nitrate base up to the 1950's when it was finally phased out. The American Film Institute and the Academy of Motion Picture Arts and Sciences (along with many others) have taken steps in order to preserve these old films, but for many of them this attempt has come too late.

It should be said that it is quite common these days for the DP's contract to include the requirement to provide a full negative. This means that underexposure as a route to providing a certain look is unacceptable to the production. You may find this offensive or restricting but I'm afraid that many producers have had a considerable amount of trouble producing first-class release prints. 

Film stock is manufactured in what are known as parent roles, usually six thousand feet long and around a meter and a half wide. The parent roles therefore need to be cut, or slit, into the required width of 16mm, 35mm or 70mm.
Though the dailies may look excellent, cinema release prints are usually made from inter-negatives, as the original negative is far too precious to use for final printing of the large quantity of prints needed by the distributor. It is very difficult to make a satisfactory inter-negative from a thin or underexposed camera negative.

It's not at all uncommon for an appreciable part of the production's' budget to come from pre-selling the video rights. A full negative is vital in these circumstances as the telecine machines used to make the master tape are very intolerant of a thin negative.

Film stock is manufactured in what are known as parent roles, usually six thousand feet long and around a meter and a half wide. The parent roles therefore need to be cut, or slit, into the required width of 16mm, 35mm or 70mm. It is usual to slit the whole parent roll into just one film width. 

Having slit the parent roll into the required width the film must then be perforated. Back at the start of the 20th century, when the motion picture industry was just emerging, one of the main areas of competition between the companies seeking to dominate the market with their format was the type of perforation used. Edison used a rectangular perforation, the French a round one and most other American companies something approaching a square perforation.

Around 1916 the Society of Motion Picture Engineers of America sought to standardize the perforation used throughout America: they chose to adopt the perforation that had been developed by the Bell and Howell company. While Bell and Howell perforation was perfect for negative stock which requires maximum accuracy and only has to run through the camera gate once and a printing machine a few times, it was no ideal for print stock which has to run through a projector many times. 

The problem was that the join between the curved section of its shape and the straight line section results in a sharp corner and this corner was prone to tearing after being run through a projector many times.

A different perforation was then devised where the shape is more square and all the corners are rounded. This gives the positive perforation much more strength though it is harder to manufacture the punches for perforating positive perforations to the same tolerances as the negative perforation. The positive perforation is known as the Kodak perforation.

For 35mm the consistency and accuracy of perforating is vital to the steadiness of the image.
Things changed with the advent of triacetate film base, as triacetate does not shrink after processing anything like as much as the old nitrate stock. The pitch of the perforations had, therefore, to be changed so that with the new base the processed negative and the unprocessed positive had, again, the same dimensions when coming into contact in the printing machine.

The long pitch (the old standard), is only used nowadays for very specialized applications such as when several film strips are run through the gate of the camera at the same time- as in some forms of process photography.

For 35mm the consistency and accuracy of perforating is vital to the steadiness of the image. The majority of both camera and projector mechanisms in use today locate the image using only the perforations. In the camera this is usually achieved by inserting register pins into two to four perforations after the claw has pulled down the film; they are then left in place for the duration of the exposure, being withdrawn after the shutter has closed and ready for the next pulldown.

In a projector mechanism the usual arrangement is to have the film pulled through the gate by a rotating sprocket, which is locked, absolutely rigid for the period the shutter is open. This is usually achieved using a device known as a Maltese cross. 

For 16mm things are a little different. While some cameras still utilize a register pin even they usually only deploy one. Some cameras manage to give very good registration without a register pin at all. Virtually all cameras, with the exception of the Mitchell and Panaflex 16mm cameras, use edge guides in the film gate to add accuracy to the positioning of the images on the negative. 

Some cameras use rigid guides both sides of the film and others use a rigid guide one side with a sprung guide the other to absorb any variation in the slit width of the film. This clearly makes the quality of the slitting process more critical in most 16mm cameras than their 35mm counterparts.

 
 
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