@warren Here's a photo. I'm pretty sure it is an IR filter as sensitivity in the NIR increased after I removed it. It was located at the bottom of the lens assembly.
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I'm sorry, correction - I chatted with the Kits initiative team and as of the v3.0 spectrometer, filters ARE still present in the cameras, so as to give folks an option, and because for some uses, visible-range spectra are better when the filter remains. For example, the Oil Testing Kit uses only visible-range data, and the filter keeps the noise down in that case.
Apologies for the misinformation! That is definitely the filter. Thanks for helping us solve this little mystery!