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Stuart,
It's not just a faulty batch.
The "mini-erf" filter element in both the Coronado and the Lunt Ha scopes seem to suffer from premature failure. No satisfactory reason has been given, but when using and/ or aquiring an Ha scope it's worth checking out.
The actual narrow band blocking filter element (between the mini-erf and the eyepiece) seems to be far more resilient and I have no record of failures.
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