My 6" reflector has a offset hole in the front lens cover and I fixed a piece of the solar film to some cardboard and very securely stuck it on underside of lenscover.
(Perhaps better would be to cut out a suitably shaped piece of plastice and bond or attach with small bolts to cover.)
The filter is protected from damage as the offset hole has its own cover.
This also saves on film, although I also made a full aperture filter also.
I couldn't see any difference in full aperture and offset.
You won't see any proms with the film -
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