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The original PST objective had an energy reduction filter (ERF) coating within the lenses. This subsequently was found to fail and the coating took on a “Rust” like appearance.
This was not directly a safely issue but did significantly reduce contrast and definition.
Meade replaced this design with one based on a non-ERF objective and placed a “mini-ERF” in the eyepiece holder. This is an ITF construction like all the ITF used by Meade. We have found the filter can fail due to moisture ingress aggravated by thermal loading and shock. The filter can last from months to years...but will eventually fail.
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