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Trevor,
DON"T USE THESE FILTERS!!
We have extensive documentation on the failure (heat cracking) of this type of filter.
They are unsafe and should be banned from distribution.
The best thing you can do is to go to the beach, hold the filter in your right hand and throw them as far as possible into the sea.
Seriously, they are dangerous.
There are some very safe ways of observing the sun - Baader solar film or a good Herschel wedge.
The specialised Ha etc. type filters are very expensive and complex (optically) and designed to function safely with most refractors.
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