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A Speed Controller For Film Projectors

Do you have old family movies on film? Have you watched them lately? You may be shocked by how much they have deteriorated over the years. They need to be transferred to DVD before the film deteriorates to the point where it is unwatchable. Video conversion is not as straightforward as you might think but this simple project enables you to do it.

by John Clarke

If you have old family movies stored in some dark spot in the house, they are bound to be rotting away. If you doubt us on this point, better crank up your old projector and have look for yourself. You will be probably be horrified at the visible deterioration. You need to act now so that you can preserve them for posterity. Transfer them to DVD as soon as you can. As a bonus, this will make it easy for you to pass them on to other family members or relatives.

You also need to consider that your bulky, old film projectors will not last forever either. Spare lamps and parts are probably now quite expensive and hard to get. And apart from that, projectors are noisy, not easy to use and not many people are familiar with their operation. So there is no alternative really – you need to convert those movies to DVD before it is too late.

Converting to digital

There are many commercial enterprises that can restore film and transfer your old films to digital format. Such companies typically use quite sophisticated techniques for film-to-video conversion and these methods are described at http://en.wikipedia.org/wiki/Telecine

Click for larger image
The Speed Controller PCB carries a PIC microcontroller, three indicator LEDs and four transistors to drive a motorised pot. The shaft of the pot then drives the existing speed control knob on the projector.

For home movies though, getting the job done commercially can be rather expensive. Fortunately, you can do the conversion yourself. It basically involves running the film through a projector and using a video camera to record the on-screen image. The resulting video can then be recorded to DVD via a computer or DVD recorder. If you don’t already have a film projector, then check eBay for a secondhand unit. However, before you leap in, you will need a projector speed controller to get good results, otherwise film speed variations and synchronisation problems will give lots of flicker.

Let’s now describe what you need to do.

The set-up for videoing a projected film image is shown in the photo on the facing page. As can be seen, the film is projected onto a screen and the video camera records the image. However, there are a couple of simple tricks to get good results.

First, the projector must be placed no more than about 250mm away from the screen, so that the video camera “sees” a bright image. This ensures that the camera operates at a relatively high luminance level for best image contrast and least picture noise. For the screen, good-quality white paper can be used.

Note that the recording also needs to be done in a darkened room to ensure optimum contrast. However, it’s not necessary for the room to be completely dark.

Our experiments showed that good results can be obtained by setting the video camera to automatic focus and exposure. It may be possible to obtain better results by setting these controls manually in some cases, although this will very much depend on the film quality. If the film exposure varies widely, then a manual exposure setting on the video camera will not be suitable.

In our case, we used a Sony Digital 8 Video Camera Recorder which records onto tape. The resulting video signal was then captured on a computer and the titles added using Windows Movie Maker, after which it was burnt to a DVD.

Of course, many people will now have a more modern camcorder that records directly to digital memory. In that case, it’s simply a matter of copying the file directly to a PC or to a DVD recorder.

Avoiding flicker

Flicker is the big problem and it is all to do with synchronisation.

Basically, the speed of the projector’s motor must be set so that the projected film rate is synchronised with the video field rate of the camcorder. In practice, this means that the projected film frame rate must be a multiple of the video field rate. If this is not done (ie, the film frame rate is not synchronised to the camcorder), the recorded video image will flicker severely

The Australian PAL-B video standard specifies a frame rate of 25Hz. In practice, each frame is broken down into two fields for a total of 50 fields per second (see http://en.wikipedia.org/wiki/PAL for more details).

By contrast, standard-8 film is recorded at 16 frames per second (fps),
while Super-8 films are generally recorded at 18 or 24 frames per second (refer to http://en.wikipedia.org/wiki/8_mm_film).

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