How to filter-out the Sodium 589, 589.6 spectral lines without Didymium filters

[NolascoCM]

Hello everyone!

I just joined SGL when looking for an eventual solution to the issue in title.

I must add here that my specific problem is attenuating, as much as feasible, the light from two sodium road lamps just over my backyard - these are the only lights present - through the use of suitable filtering glasses, so that to be able to freely look to the sky (increasing my retina sensitivity).

Having spending some time searching the net, the only filters I have found are the Didymium based ones used for glass work. Unfortunately these are not easy to find in Portugal (even in Europe) and a little expensive (I found a suitable model, sold by a French company at around 100 Euro).

Does anyone know a cheaper alternative (even if not so efficient).

Regards to all,

Sérgio Nolasco

PS: I hereby confirm that I read the CoC and I will abide by it!

[ronin]

Do not think you can do it with 2 filters or more, and, if you could - sure not possible) by the time you get 2 filters with the correct transmission curves they would cost more.

Look at the CLS filtrers: TS-CLS

The blocked spectrum seems a bit wide so you will get a colour imbalance with the one linked to.

Another option is the Baader Moon and Skyglow filter. The cut at the Na lines is better (narrower) but it seems to reduce a bit of the blue/gree also. Also not sure of the cost.

Another that seems a bit selective on what it chops out is the IDAS LPS P2.

All will alter the colours of what you look at.

Skys the Limit do 2 CLS filter, the "standard" one looks to have a similar curve to the TS one, but Skys the Limit do a premium one, which I would half expect to have a narrower cut but there is no transmission curve set.  Also not sure if they ship to Portugal.

[NolascoCM]

Hello Ronin,

Thank you for your advice and suggestions.

I've checked the TS-CLS filters (Sky's the Limit seems out of business) and, although they will certainly filter-out the Na lines they will also filter out a lot more (at least all the range 530 - 610 nm). And, in your line of though, as I add more hardware the price will go up; in my case I'll need two of them (one for each eye, as I'm not seeking out for photography - just seeing, eventually using some equipment), and at least with 50 mm / 2 inch diameter (to fit regular protection glasses), what will lead to another slight price increase.

Do you know anyone has tried using a pair of glasses as these, and just observe through them (then it would not be necessary to fit filters to equipment and one would gain dark sensitivity - for me this is the main issue). The question I have about these glasses is about their transmission curve (that I didn't found); what do they filter out besides the Na lines?

Best regards and thank you again,

Sérgio Nolasco