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Celestron LPR Filter Question

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#1 nic35

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Posted 13 February 2018 - 11:02 AM

I'm looking for information (transmittance curves, user guide) on an old Celestron LPR filter - titled "LPR Filter Model B.  Number 94127". 

 

It screws on the rear cell of a SC.

 

I also see that there is a 94127A.  Anyone know the difference

 

Thanks in advance

 

john



#2 MrJones

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Posted 13 February 2018 - 11:28 AM

Model A was 1.25" and B was the SCT version. These were the first non-laminated LPR filters from Celestron and were made in Japan. Optics Planet has an old page with representative spectrum https://www.opticspl...pr-filters.html Hope this helps.

 

Add: I'm a little confused as 94126A also seems to be 1.25". Maybe they changed the product codes at some point.


Edited by MrJones, 13 February 2018 - 11:30 AM.


#3 nic35

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Posted 13 February 2018 - 12:16 PM

Thanks.

 

john



#4 Starman1

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Posted 13 February 2018 - 06:03 PM

It's a broadband filter, and time has, unfortunately, made these far less effective at reducing light pollution.

A recent measurement of the light in the sky of Los Angeles found over 600 different spectral lines of LP in the sky:

mercury vapor, high pressure sodium vapor, low pressure sodium vapor, high temperature LEDs, low temperature LEDs,

LCD billboards (the worst!), fluorescent bults, incandescent bulbs, halogen bulbs, etc. (even aurorae and oxygen glow).

Back when almost all LP was incandescents and mercury vapor, it was easy to put a notch in the spectrum and reduce the LP.

Today, the effectiveness of these LPR or broadband filters is reduced to being photographic accessories for already quite-dark sites.

 

Very narrow filters are necessary for viewing nebulae in urban environments (e.g. H-ß, O-III, UHC) or for imaging (H-α, S-II, N-II, O-III all with extremely narrow bandwidths)

With the nature of modern light pollution, the older LPR filters may actually make matters worse by scattering light of wavelengths passed through.

I'd save the filter for dark skies and use narrower filters for viewing nebulae in an LP environment.

[I've used a narrow UHC filter in skies where the naked eye limit was 2 to 2.5, and the sky was blue (!) at night, and the filter worked decently on some of the brighter nebulae.]


Edited by Starman1, 13 February 2018 - 06:04 PM.

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