Epson STYLUS SCAN 2500 User Manual page 129

Leave the opening shown below uncovered, otherwise the colors in
your scans will be affected.
Scanning normal (reflective) documents
When you return to scanning normal reflective documents, you
can simply turn off the Film Adapter, then place documents
between it and the document table. If you will not scan
transparencies for long time, you can remove the Film Adapter
and store it in the original package.
Remove the Film Adapter in reverse order as described on
"Installing the Film Adapter".
Note:
When scanning thin documents, you may see an impression of the
underside of the Film Adapter in your scans. If so, change to using the
document cover instead of the Film Adapter.
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Scanner
opening