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Slide projectors

Auto-focus runs wild

If your projector's auto-focus starts running continuously every time a slide drops in to project, you may not have as major a problem as you might expect.

This paragraph will help you determine if this tip might apply to you. First, you must have an Eastman Kodak projector that is new enough to have a removable lamp module (not just a door for access to the lamp itself). These are models like the Ektagraphic III series and the Carousel 4000 series projectors. If your model is a AF2, 850, 650 or something like that, this tip doesn't apply. Next, your projector's auto-focus must only misbehave when the projection lamp is on and a slide is inside. It must not continue to run when the lamp is off, or without a slide in the gate (which will close the shutter to block off the light).

Now that you've determined this applies to you, here's a very simple way to solve your problem in the majority of cases: Replace your projection lamp with a new one! That's it. Okay, it sounds too simple and doesn't seem to make sense, but there is really a good reason for this.

The way the auto-focus is designed on these models, it relies on the correct amount of light being emitted through the reflective coating on the side of the lamp. As a lamp gets old, the reflective surface burns off and eventually it is nearly just clear glass. This allows too much light through and can confuse the auto-focus circuitry which uses a photoelectric cell to detect light reflecting off of the slides surface.

If replacing the lamp doesn't solve your problem and you have access to another slide projector with the same type of removable lamp module, you have one more thing to try. After installing new lamps in both modules, try swapping the lamp modules from one projector to the other. If the malfunctioning projector now works properly you have found the source of the problem. Stray light may be escaping from the original lamp module, effecting the auto-focus operation. The auto-focus circuit is very critically aligned, but if varies from projector to projector. You may even find that the module that won't work in one projector, works fine in another. In that case, just leave them where they work, if possible. Otherwise the only solution is to replace the entire lamp module with a new one, which is fairly expensive. However, you still will have saved yourself the cost of a technician's time to find the problem for you!

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