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Light Pollution Filter Spectral Comparison

astrophotography imaging equipment imaging/sketching contest LP dslr dso ccd beginner CMOS
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#1 anrran


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Posted 12 April 2020 - 10:44 AM



I'm not sure if this is the right place to post this or not, but I'm kind of new to astrophotography and this is a beginner forum after all. I've dabbled a little in the past but wasn't that serious about it. Since this quarantine is going on, it got me rethinking about it again (since I have nothing else to do), so I started researching equipment online. I live smack in the middle of Houston (pure white on the light pollution maps, not even antique white) so obviously my first research topic was light pollution filters. There seems to be many on the market these days and a few recommended by popular YouTubers like AstroBackyard, AstroStace, etc.so these are the ones I narrowed in on with my research. One thing that keeps annoying me though is the pictures of the spectrum of these filters suck most of the time and it's somewhat tiresome flipping between different websites to compare them. Even then, figuring out where the peak of one filter is in relation of a similar peak of another filter is gets confusing.


So in my boredom and imprisonment at the moment I downloaded a program called Graph Grabber which can take pictures of graphs (i.e. LP filter spectrum pictures) and turn them into data points that you can plot in any plotting software (in my case, Excel) that you have. Basically you click on the min and max points of the x and y axis of the picture, then you click at various points along the spectrum. The program uses all your clicks to create data points that you can export to a file, which then you can plot in Excel. I did this for all the popular filters currently on the market so that I can compare them without flipping to different websites. However, the plots are only as accurate as the quality of the picture I used (in some cases terrible, surprisingly more so the more expensive the filter) and my clicking prowess (which is "impeccable", unless it's 1 am in the morning). Attached is an Excel document with the spectral graphs plotted (solid lines) alongside the most common light pollution sources (dashed lines) and emission spectra (dotted lines). I created three graphs each, one for Duo, Tri, and Quad band filters; one for multi spectral filters; another for generic light pollution filters. These are separated by three different tabs in the spreadsheet (just click on what tab you want to view). I also have all filters for each graph showing, which makes it super convoluted. You can turn whatever ones you want on or off by clicking on a white space in the graph, select Design under Chart Tools in the top ribbon, click Select Data. A menu pops up with check marks next to filter names; just uncheck whatever filters you want to remove from the graph, and click Okay. The plot should update to reflect your changes.


Duo, Tri, Quad band filters:

Altair Astro Quadband

Altair Astro Triband

Hutech IDAS EAO1

Hutech IDAS NB1

Hutech IDAS NB2 + NGS1

Hutech IDAS NB3 + NGS1

Optolong L-eNhance

Radian Triad Triband

Radian Triad Ultra

STC Astro Duo Narrowband


Multi Spectral filters:

Hutech IDAS LPS D1

Hutech IDAS LPS D2

Hutech IDAS LPS P2


Optolong L-Pro

Skytech L-Pro Max

STC Ultra Layer Astro Multispectra


Light Pollution filters:

Altair Astro CLS

Astronomik CLS

Astronomik CLS CCD

Astronomik UHC

Astronomik UHC E

Hutech IDAS LPS V4

Optolong UHC

Skytech CLS


I'm not sure if anyone did this already, but I couldn't find anything when I searched for it. Hopefully this will help some of you to choose the correct filters you want to buy. And if there are any mistakes, it's not my fault....






Attached File  LP_Filter_Spectral_Comparison.xlsx   165.06KB   58 downloads

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#2 TelescopeGreg


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Posted 12 April 2020 - 02:58 PM

Thanks for doing this!


Question:  Is there an "easy" way to enable / disable the individual filters, to untangle some of the graphs?  Editing the data ranges can work, but it's kind of clumsy...  (I'm using LibreOffice, by the way.)

#3 anrran


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Posted 12 April 2020 - 04:18 PM



Unfortunately, I am not really familiar with how LibreOffice works. I did just download it to play around with it. The only thing I can find so far is to just delete the plots you don't want from the data ranges, but like you said that is not ideal especially if you want to bring them back up. I don't see an option like in Excel to just check or uncheck them. You could also right click on the line you want to "remove", click format series and change the transparency to like 75% or something so it almost goes away. Or change the line color to white. Trying to click on the line to find it again is kind of difficult though. Maybe someone with more knowledge on the software than me could chime in. It does seem like a basic function that the software should be able to do. Sorry I couldn't help much.



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