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Scratch Test: Difference between revisions
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If your scratch test passes, you can save your film to use again. | If your scratch test passes, you can save your film to use again. | ||
Loop Method | ===Loop Method=== | ||
Prepare a loop of film to run through the entire length of the projector, including rollers on reel arms. Set up platter rollers to guide the film away from any projector surfaces, or cover surfaces with lens tissue to avoid scratching. Start and run the loop several times (50-100 is ideal), and check for scratching on screen or by shining a flashlight on either side of the film as it leaves or enters the projector. | |||
Because soundhead flywheels will take a few seconds to come to speed, at least a few feet of your loop will inevitably scratch at startup and can be ignored, though if they are visible on screen in one pass it would be cause for concern and further investigation. For 70mm scratch tests with DTS only, this is not a concern because no flywheels are involved. | Because soundhead flywheels will take a few seconds to come to speed, at least a few feet of your loop will inevitably scratch at startup and can be ignored, though if they are visible on screen in one pass it would be cause for concern and further investigation. For 70mm scratch tests with DTS only, this is not a concern because no flywheels are involved. | ||
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This method is most useful for evaluating [[Slap Scratches]] or any scratches with a repeating pattern. | This method is most useful for evaluating [[Slap Scratches]] or any scratches with a repeating pattern. | ||
Reel to Reel method | ===Reel-to-Reel method=== | ||
Prepare 50-100' of test film on a house reel. Project as normal, rewind, and repeat several times (50-100 is ideal, 10-15 may be more practical). Check for scratching on screen and/or on the bench when rewinding. Keep track of base and emulsion side so you can evaluate if anything shows up. | |||
This method is most useful for evaluating vertical scratching cause by rollers and flywheels. | This method is most useful for evaluating vertical scratching cause by rollers and flywheels. | ||
Spot Check Method | ===Spot Check Method=== | ||
Prepare ~50' of test film on a house reel. Run enough film through for the flywheel(s) to come up to speed and let run a few seconds longer. Stop the projector, and with a sharpie, carefully mark each point of contact with the film (sprocket, roller, gate, etc.). Carefully remove the film and inspect for scratches. If a scratch appears, take note of where in the film path it occurred and evaluate. Using this method the flywheel will inevitably scratch the film when the projector is stopped. | |||
Visual Evaluation of Film Path | ===Visual Evaluation of Film Path=== | ||
Because the above tests do not take into consideration running a full reel of film, and it would be impractical to use 2000' of expensive film stock to run a scratch test several dozen times, a careful and thorough check of a known good test reel should conclude the scratch testing process. Run a full reel of film and examine the film path as it plays: Are all rollers turning? Are the arms aligned so that the film is completely clear through the entire reel? Is the film entering the projector evenly? Look for any new scratches or other issues on your test reel. | |||
Diagnosis | ==Diagnosis== | ||
If a scratch test reveals that a projector is scratching film, the next step is to determine the cause. | If a scratch test reveals that a projector is scratching film, the next step is to determine the cause. | ||