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Filter for NV?

NV
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#1 Jim4321

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Posted 09 May 2019 - 05:59 PM

Would this be any use for night vision astronomy? 

 

And how the heck do they do it? Some kind of polarization?

 

  https://smile.amazon...=8-1-fkmr1&th=1

 

It's about cheap enough to buy just to play with, but I figured I'd ask here, first.

 

Jim H.

 

  


Edited by Jim4321, 09 May 2019 - 06:00 PM.


#2 TOMDEY

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Posted 09 May 2019 - 06:36 PM

I looked around just a bit and am, admittedly, puzzled! Could find no actual tech data, patents, etc. Making the ads come across as cryptic, even to the point of seeming evasive or simply ill-informed. If I were still at work, with access to spectrophotometers, etc... would certainly run traces!

 

With that background... I am just guessing that it comprises traditional angle-adjustable crossed linear polarizers with integral dye filtration. It sure seems ingenious, if it really does (efficiently) what they seem to be claiming... especially at the dirt-cheap price!

 

NOTE: The extinction of traditional crossed linears is undoubtedly wavelength-dependent. It might be that is really all they are doing, just putting a wavelength scale on it, rather than the more-traditional ND scale... The more I ponder this... the more convinced I am. That idea would actually be patentable as "novel use of an existing device"  --- quite possible patented fifty or more years ago?!    Tom


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#3 TOMDEY

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Posted 09 May 2019 - 07:05 PM

OH! Regarding Night Vision use: I have a feeling that the throughput is very low... so that buying a set of individual IR cut-on filters would (technically) be the way to go, for NV use. I bought a set from Thor Labs cut-off (not cut-on) filters for a different application --- VERY expensive! Picture here shows just a couple of them.     Tom

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  • 50 Thor Labs NIR cut-off filters for M1 Crab Pulsar.jpg

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#4 TOMDEY

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Posted 09 May 2019 - 08:16 PM

Ehhh... another comment. If you have the luxury of access to a spectrophotometer, note that many/most comprise polarization elements internally. If you are measuring non-polarizing filters, that is fine. But if you are measuring polarizing filters, will need to stick additional components into both the test and reference chambers in order to correctly assess the test filter. And that can get complicated... involving such things Stokes Parameters, Jones Matrix, etc. etc. I found that out the hard way and then had to research, understand and modify our (Cary 14 Double Beam) Spectrophotometer, to properly report spectral throughput, as a function of polarization state!

 

This optics stuff gets annoyingly complicated, when one has to dive headlong into the details of how nature actually behaves!    Tom


Edited by TOMDEY, 09 May 2019 - 08:19 PM.


#5 slavicek

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Posted 10 May 2019 - 08:07 PM

Wow, $26 miracle filter? If you have time, give it a try! And let us know how it performed with NV wink.gif




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