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There are many suggestions in astrophotography forums to use didymium filters ("Red Enhancers", made by Hoya or Marumi) to decrease the influence of sodium vapour lighting.

However, they are hard to find in Europe. I've read in a single forum post that the glass used in those filters is supposed to contain arsenic and could no longer be made or sold because of that. I could not find further sources for that claim.

Can anyone here confirm this, ideally with pointers to reputable sources? And even if there is arsenic in the glass, would it be dangerous in everyday use?

  • I would think eating the glass would be more dangerous than anything encapsulated in it. (I'll be here all week, don't forget to tip your waiter!) – James Snell Sep 8 '16 at 10:17
  • I just edited my question to make it a bit clearer: The claim I'd like to verify or disprove is that the alleged arsenic content in the glass leads to actual interference from European control agencies, forbidding the manufacture and sale of those filters. – jstarek Sep 8 '16 at 13:49
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Didymium gets its name from being composed of two of the lanthanide elements, praseodymium and neodymium. These are not particularly poisonous, and are quite safe bound into solid glass.

B&H Photo-Video mentions that Tiffen and Lee sell these filters as "enhancing filters" and Singh-Ray calls them "intensifying filters".

You might also try a sodium notch interference filter to block the ~590 nm Na lines. These filters are also available from Thor Labs, Edmund Optics etc.

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  • Thanks, and would you also consider potential arsenic contents in the base glass material safe as long as the glass doesn't break or otherwise disintegrate? – jstarek Sep 8 '16 at 13:50
  • Silicate glasses effectively lock up trace metals very well. Unless immersed in hydrofluoric acid, alkali metal hydroxides etc., the components of glass are well bound. It is even used for storage of radioactive wastes (sheffield.ac.uk/news/nr/…). Just don't cut yourself on any broken glass, nor should you run with scissors. – DrMoishe Pippik Sep 8 '16 at 20:55

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