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TheThing

Solar filters and Newts

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Just a couple of, hopefully, quick questions: -

- I'm assuming that there are no known problems with using a full apature Mylar solar filter with a Newtonian reflector at all?

- If the Mylar where to devolp pin-***** holes in it, is it beyond saving or is there some sort of repair that can be carried out? I seem to recall mention of going over them with a marker pen, but I'm not sure if this refers to something else!

Thanks in advance!

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I'm assuming that there are no known problems with using a full apature Mylar solar filter with a Newtonian reflector at all?

- If the Mylar where to devolp pin-***** holes in it, is it beyond saving or is there some sort of repair that can be carried out? I seem to recall mention of going over them with a marker pen, but I'm not sure if this refers to something else!

FYI Baader solar film is not mylar ...

You still need to take care that the filter is in good condition before each and every use; to remove the finder unless it has its own solar film filter; to ensure that solar film filters are fixed in place so that the cannot be accidentally disloged or blown off by wind gusts. (And that applies to all scopes, not just Newtonian reflectors!)

A few pinholes are of no consequence, contrast loss will be an issue before there is a danger to eyesight. But splits or cracks of any size are not permissible; check in particular for gaps developing between the film and the mount round the edge.

Pinholes can be "spotted out" with black marker pen, drops of paint etc. for the purposes of maintaining contrast. If the total area is sufficient to present a hazard (we're talking a couple of square millimetres) then it's better to replace the film. But Baader solar film is pretty resistant to pinholes (it's coated on both sides, so a tiny hole in the coating on one side is of no consequence) ... it does however go brittle over a period of some years, as does any plastic exposed to strong ultraviolet light from the sun. Chemical fumes from cleaning products will also affect the long-term stability & resilience of the plastic base material.

In practice (& with reasonable care) the limiting factor of the lifetime of Baader solar film is that it is impossible to clean; dust & grime buildup will likely result in needing to replace it before aging of the substrate or deterioration of the reflective films.

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It's actually a Celestron film, not Baader and it says Mylar in the instructions IIRC.

Thanks for the ino though Brian, very useful as always.

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You can also use an off-axis aperture mask with a smaller filter on it, this is a lower cost option if you are trying to save some $$$.

Dan

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It's a bit like that ad for a small car "sounds like a Golf, looks like a Golf" but it's not....:D

Baader Solar Film as Brian points out is a proprietary film coated on both sides and is definately not a piece of your average gladwrap aluminised!

My Baader film is over five, no six years old - no pinholes, no problems - it is a Golf;)

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