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Reels and cores are the primary tools used to hold lengths of film. Because they are so fundamental, there are many types. They may hold as little as 50 feet of film (for example, for 16mm trailers or a Super 8 home movie) or as much as 18,000 feet (for use with a 35mm long-play tower system in a multiplex setting).
Shipping reels are used to when shipping 35mm and 70mm film between depots, archives, and venues. They can be made of steel or plastic, though plastic shipping reels are more common. Shipping reels are designed for shipping, and are not recommended for projection.
Show reels, also called house reels are used for projection. In 35mm & 70mm settings today, a typical show reel is a 2000 foot metal reel. In small gauge settings, a show reel may simply be the sturdiest, most true reel of appropriate capacity the projectionist can locate.
Split reels are used when working with film on cores — for example, to transfer film from a core to a reel for exhibition. Split reels are not recommended for projection, but you should have one on your bench. They exist for all film gauges.
Reels are typically referred to by the length of film they can hold (ex., 35mm house reels are called 2,000’ reels). However, this nominal value is only an approximation. The actual capacity of a reel is determined by its hub size, flange diameter, and the thickness of the film.
While the variation between reels that have a nominal capacity of 2,000’ is not great, this can become a factor when reels are overfilled beyond 2,000'. For example, when building up a reel of trailers, you may be able to fit more on the feed reel you’ve prepared than can fit on the take-up reel if it’s a different style, even though both are nominally 2,000’ reels. This variation is most easily demonstrated when dealing with split reels, since the capacity of the reel will vary based on core size selected. As an example of the range in capacity of nominal 2,000’ reels, a 15” split reel with a 2” core can hold roughly 2,729’ of polyester film, while a 15” Goldberg house reel with a 5” core can only hold 2,470’, and an older Goldberg house reel with a 14” diameter and a 4” hub can only hold 2,223’ of film.
This becomes more of a factor when building up film to larger reels, or when handling prints that have been improperly broken down from large reels or platters, as some projectionists had the bad habit of breaking down a print by spooling onto each shipping reel until it seemed full (potentially overfilling it) and then cutting it at an arbitrary point instead of finding and separating the splices between reels. It is common for projectionists to refer to any reel that can fit 3-4 shipping reels as a 6,000’ reel, but the actual capacity can vary significantly. For example, a 25” Goldberg E-Z hub reel with an 8” hub can hold 6,938’ of polyester film while the same reel with a 5” hub can hold 7,409’.
The variance from nominal capacity is also more of a consideration when comparing reel capacity for different film bases, since polyester is thinner than acetate, and acetate is thinner than nitrate. To a lesser extent there is also variation in base thickness between manufacturers. The thickness of the emulsion layer is another factor (this can be observed during projection when the change in depth causes the focus to drift between stocks). Magnetic tracks will also add to film thickness.
Roll Size Calculation
The diameter of a roll of film can be devised using the following formula:
- D is roll diameter in inches
- L is length of film roll in feet
- t is film thickness in inches (about 0.0053 for Kodak 2383)
- C is core/hub diameter in inches
Alternatively, the total length of a roll of film or the total capacity for a reel can be calculated as:
Examples of film thickness:
- Kodak 2383
- Kodak 35mm polyester base thickness = 0.0047”
- Kodak 2383 emulsion thickness = 0.0006”
- Total thickness of Kodak 2382 stock = 0.0053”
- Kodak 35mm triacetate base thickness = 0.0056”
- Kodak 16mm triacetate base thickness = 0.00525”
Reels & film damage
Unmaintained reels can be a source of film damage.
- Reels with center hubs smaller than 4 inches are not recommended for projection (they can cause too much tension to be placed on the film) or for long term film storage (they can cause base curl).
- Flange-to-hub ratio - On traditional mechanical projectors, the clutch must be adjusted so that the tension is not too great when the reel is empty and not too slack when the reel is full. To achieve this, reels should have a flange diameter to hub diameter ratio of no more than 3:1. For larger reels, this can be cheated somewhat by using floating hubs because the mass of the flanges is less of a factor during the initial take-up, allowing a lower starting torque.
- Inspect all reels regularly to make sure they are true and don't have any sharp burrs that might snag or rub on film. If burrs are discovered, sand them down with 600 grit emery cloth or crocus cloth. If the burr is large, first use a file and then sand down to a smooth finish. Do NOT do this in a film handling area to avoid print contamination.
- Dirty or rusty reels - House reels should be kept clean. Shipping reels that are dirty should be thoroughly cleaned after the film has been wound off. Rusty reels should not be used.
- Bent shipping reels - For bent steel shipping reels, it may be possible to gently bend them back by hand. If the lip of the flange is crushed or bent, do NOT use tools directly against the metal, which can create burrs. Instead, wrap a piece of felt around the flange and sandwich it between two pieces of cardboard so that the tool does not mar the surface of the reel.
- Broken clips on plastic reels - For plastic reels with detachable flanges, the clips holding the flanges to the core often snap off. Instead of spooling off of the damaged reel, remove flanges and place the core on a split reel. Ship the film back on a replacement reel or rewind onto a split reel and transfer the core back to the broken flanges, zip-tying the flanges to the core for safe return shipping.
- Broken two-piece plastic reels - Plastic shipping reels that consist of two pieces of molded plastic glued together at the hub can split in the center. Use a zip-tie to stabilize the reel well enough to spool the film off, and return the film on a replacement reel.
- Cracked plastic flanges - Tape the inside edge of any cracks so that the film doesn’t catch on a sharp edge during rewind.
- Shattered flanges - For reels with detachable flanges, remove the flanges and transfer the core to a split reel. For plastic reels with fixed flanges, you may need to get creative to find a way to safely spool the film off without striking the jagged edges. For example, card stock can be cut to match the shape of the reel and secured between the film and the broken flange.