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Filter Comparison For Imaging Broad Spectrum Objects In Light Pollution Areas

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#1 JTYoder2017

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Posted 07 May 2019 - 12:05 PM

The primary purpose of imaging with a filter in the city is to mitigate light pollution and help suppress the noise so that the signal of the target object becomes easier to identify. This is rather easily achieved for nebula type objects that emit at very specific wavelengths but much more challenging to accomplish for full-spectrum sources such as galaxies and globular clusters. Cutting down on city glare is becoming even more challenging as city lighting transitions from Mercury type lighting that emits at defined wavelengths to LED lighting that generally emits broad spectrum lighting.

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#2 Gork

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Posted 07 May 2019 - 06:46 PM

Timely article for me.  Because of health concerns I had to give up my own observatory in Benson, Arizona (40 miles east of Tucson) and move back in to town.  I still have my own observatory, but I am only blocks from the UofA campus.  I wrote the two articles entitled "My Other Telescope is an 8.4 Meter" so I have lots of experience at the macro level but am still learning the basics in my own project.  I just made the switch from DLSR to ASI178MM monochrome with filter wheel and have to choose which light pollution filter to put in my optical train.  I had decided upon the CLS-CCD but only based on anecdotal information.  Your analysis validated my choice, and now I feel much more confident that I've made the right choice.  Thanks for the hard work and much needed objective data.



#3 JTYoder2017

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Posted 07 May 2019 - 09:31 PM

Thanks for the feedback.  Glad some else can benefit from the analysis.

 

James



#4 bobzeq25

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Posted 07 May 2019 - 10:45 PM

Good stuff.  I trust you don't mind my referencing further information.

 

More useful information, including more quantitative tests, in this thread.  Some of the best imagers on this site (which does not include me <smile>) participated.

 

https://www.cloudyni...-the-answer-is/

 

More information.  Here the issue is sharpness.

 

https://www.cloudyni...adband-targets/

 

Bottom line.  People's opinions on broadband LP filters vary.  Some serious imagers use them, some don't, even in light polluted skies.  Some only use them on emission nebulae, where they work best.  I suggest trying one on various targets, and evaluating the results in your final images, which is what counts.  The workflow used in this test is excellent, it included gradient reduction, which is essential.

 

Which one?  That gets harder.  One impact of broadband LP filters is that they, operating by ripping out chunks of the spectrum, distort colors.  You can adjust things for a reasonable result, but some data is just gone.  The stronger the LP filter, the more it distorts color.  As is so often true in AP, there are tradeoffs.



#5 Prasad

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Posted 08 May 2019 - 07:20 PM

Perfect timing that I stumbled on this great report. I have been an ATM all these years and started playing with an equatorial mount recently. Then added a GOTO drive to it using OnStep. I now want to attempt imaging. Initially I thought I couldnot because I live on the east coast near bright city like Philadelphia. Today I found this report. Wow, I think I will not give up on imaging if filters can help me get over light pollution. Thank you JTYoder2017 for this.



#6 FlankerOneTwo

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Posted 10 May 2019 - 07:49 PM

Nice work, thanks for the report. Any plans to include the IDAS LPS-D2 and Optolong L-Pro?



#7 JTYoder2017

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Posted 11 May 2019 - 03:33 AM

Thanks

Just testing the equipment I have.  The filters you mention do look like interesting filters.  There is a very nice review on filters including these here.



#8 jimthompson

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Posted 16 May 2019 - 07:01 PM

Your results are consistent with my findings under even higher light pollution levels, the Astronomik UHC provides superior performance.  Very nicely done!

 

Cheers,

 

Jim T.



#9 DonBoy

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Posted 22 May 2019 - 10:54 AM

Very interesting report.  I found similar results with the Astronomik UHC + IR Block combo.  

 

https://www.cloudyni...t/#entry9088790

 

BTW why are you listing the Astronomik UHC as a Astronmik UHD?  Did I miss something?

 

Thanks,

 

Don



#10 JTYoder2017

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Posted 22 May 2019 - 11:02 AM

Typo,  This should be UHC.  thanks for pointing that out.



#11 ChrisPA

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Posted 07 June 2019 - 08:14 PM

I've been on a bit of a galaxy hunt lately - I image from suburban Philadelphia under a Bortle 7 or Bortle 8 skies (different sources say different things). I image in monochrome and currently have a dual setup going on. I'm using a Baader Moon & Skyglow in lieu of a luminance filter on my Newt and ZWO 1600 combo and a Chroma LoGlow for luminance on my 8" RC and and QHY183. I don't have hard and fast scientific data, but I definitely feel like I'm getting a better SNR using those filters in place of a luminance filter - the L channel is much easier to process overall than it used to be when using a regular L filter.

Some images I've done this galaxy season with the Newt/ZWO/Baader Moon & Skyglow:
https://www.astrobin.com/395753/
https://www.astrobin.com/402244/
https://www.astrobin.com/408397/

And with the 8"RC/QHY183/Chroma LoGlow:
https://www.astrobin.com/399142/
https://www.astrobin.com/399949/
https://www.astrobin.com/407870/
https://www.astrobin.com/408909/

I'd definitely recommend them - that Baader M&SG should be part of every astroimager's arsenal. 


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#12 JTYoder2017

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Posted 07 June 2019 - 08:51 PM

Those are some mighty fine images you have there!


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#13 jtrezzo

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Posted 12 June 2019 - 01:14 PM

Hard to really make much comparison as the images are not calibrated or stretched hard enough to really see the difference. To me no filter or M&SG looks best, but again I can't really tell without larger images.

 

I've used all of these (or a similar variant) in the past except the Triad, and I'm always going to advocate for no filter, or a mild one like IDAS or M&SG in really bad LP, as the destruction of color is not worth it.

 

Personally I would completely disagree with your conclusion and would NEVER use a UHC for broadband objects period, anywhere, and probably not a CLS either. I would definitely never use a filter at all for broadband in Bortle 4. I learned that no filter is needed even in Bortle 7: https://www.astrobin.com/314853/ https://www.astrobin.com/377153

 

I look back on the ones I did in Bortle 7 with a filter and it bothers me that the color is off. Looking at the images I've done with no filter I feel much better about them.


Edited by jtrezzo, 12 June 2019 - 01:14 PM.



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