Nikon LS-4500AF User Manual page 52

6. Using the Film Holder
To replace a tray, pull the sliding spring catch forward to release the tray,
remove it, replace with a new tray, and secure it with the sliding spring
catch.
Step 2
When a tray for one frame is fitted, check that the turntable and the back
side of the depression in the tray do not interfere with each other.
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Film Scanner LS-4500AF User's Manual