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Favorite Light Pollution Filter for EAA?

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#26 Censustaker

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Posted 20 February 2016 - 03:35 PM

The red 25 or 29 works great on galaxies, cheap too.

I'm in a light polluted area too and I cannot go over x64 at low f numbers when using any gain and using any of my LP filters as it whites out, too! The only exception to that is an H-a filter or one of the red filters
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#27 jimthompson

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Posted 20 February 2016 - 03:44 PM

Hi Alistair,

 

Unfortunately the way that the spectral response is illustrated for that Castell brand UHC does not allow us to know how the filter responds to IR.  If you want the filter to perform well on galaxies you need good response to infrared.  The only filters which are confirmed good performers on galaxies are, in rough order of progressively narrower band pass:

 

- Astronomik CLS

- Antares ALP

- Orion Deepsky Broadband

- Meade Broadband

- Lumicon Deepsky

- Optolong CLS

- Optolong UHC

- Astronomik UHC

- Meade Narrowband

- Meade O-III

 

I tested the two Optolong brand filters myself so I know how they perform.  I wonder if the Castell brand UHC is in fact made by Yulong just like the Optolong brand?

 

Another alternative is to look at long pass filters.  You can start with a #29 Dark Red and see how it does.  It should perform pretty well on galaxies and emission nebulae.  The view will be red though, of course, so you will probably want to reduce your saturation to make the view greyscale.  If the #29 works but you'd like even more LP rejection, you can start looking at high pass filters with even longer pass bands.  Baader and Astronomik each sell an IR filter for use on solar system objects but it can also be used on galaxies.  I started down the road of IR high pass filters by purchasing a cheap 4 filter set off Ebay, "IR filters" meant for terrestrial photography.  I think it cost me about $35USD for the 4 filters, 650nm, 680nm, 720nm and 760nm.  They were not exactly the correct size so I cut them down using a Dremel tool.

 

cheers,

 

Jim T.


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#28 Kaikul

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Posted 20 February 2016 - 04:39 PM

 

- Orion Deepsky Broadband

 

 

 

Did you mean "Skyglow" Herr Thompson?  :grin:

 

If so, here is one you might want to look into Alistair. Perhaps he could get it shipped to you at just a slightly increased cost.

 

http://www.cloudynig...-made-in-japan/



#29 jimthompson

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Posted 20 February 2016 - 04:43 PM

Yes, sorry Orion Skyglow Broadband.  It is a wide band filter but has good response to IR.

 

In the end, if you can afford it, it is worth going all the way to the Astronomik UHC in my opinion.  If not, the less expensive options will work but at a reduced level of performance.

 

cheers,

 

Jim T.



#30 RafaelP

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Posted 24 February 2016 - 02:21 PM

Ended up purchasing and using the Orion Skyglow imaging filter with my ASI224.  I like the natural colors, and it has done a decent job as a general LP filter.

 

I have several new filters to try with both the ASI224 and Ultrastar mono.  

 

-Astronomik UHC

-Astronomik 6nm H-a

-Baader IR pass filter 685nm

 

I will report back when the clouds finally part!

 

~Rafael


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#31 jimthompson

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Posted 24 February 2016 - 02:53 PM

Very nice Rafael.  Please let us know how you make out!

 

cheers,

 

Jim T.

 

p.s.  I used a 650nm IR pass filter a couple nights ago during the full Moon.  With the added capability of stacking on the fly using SharpCap, I was very happy with the results.



#32 StarCurious

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Posted 24 February 2016 - 06:09 PM

Yes, sorry Orion Skyglow Broadband.  It is a wide band filter but has good response to IR.

 

In the end, if you can afford it, it is worth going all the way to the Astronomik UHC in my opinion.  If not, the less expensive options will work but at a reduced level of performance.

 

cheers,

 

Jim T.

 

Orion also makes a Skyglow Imaging filter, which RafaelP just ordered. The Orion Skyglow Broadband costs less than the Imaging one.  Would the broadband one (for eyepiece as well) work for EAA?

 

I already have Lumicon UHC, O-III for eyepiece use.  Would either one improve EAA in light polluted sky?



#33 RafaelP

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Posted 24 February 2016 - 07:31 PM

I have had the Orion skyglow imaging filter with the asi224 for 5 months now. I like it a lot, but it is a broadband general use filter. The other filters are much more specific in the wavelengths they transmit.

I think the lumicon UHC and OIII are a fine way to start.

Edited by RafaelP, 24 February 2016 - 07:34 PM.


#34 jimthompson

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Posted 24 February 2016 - 07:35 PM

Personally I don't recommend the Orion Skyglow Imaging for EAA as it blocks IR and is not all that narrow a filter.  You can get much better LP reduction with other filters.  The Skyglow Broadband will work well for EAA; not as narrow as say an Astronomik UHC but still pretty good.

 

The Lumicon UHC will perform poorly if used for EAA because it does not pass Halpha or infrared.  An O-III filter in theory will improve contrast on emission nebulae but only those rich in O-III so planetary nebulae mostly.  You are much better off using something else that also passes Halpha so you get a full colour view of the object.

 

Regards,

 

Jim T.



#35 JonNPR

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Posted 24 February 2016 - 08:25 PM

Jim, do you view the Lumicon Deep Sky filter as useful for EAA general LP help in red zone/residential and suburban locations? I had thought I read you mentioning it positively in this regard in an earlier post. 

 

Jon



#36 jimthompson

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Posted 24 February 2016 - 11:24 PM

Hi Jon,

 

Yes, the Lumicon Deepsky is a useful filter for EAA.  There are several people that I know who use that filter regularly.  For my location where the skies have a limiting magnitude of around +3.5 at the zenith, I find the Lumicon Deepsky to be not enough LP reduction and tend to use either an Astronomik UHC or Meade O-III (which by chance passes Halpha and IR) filter instead.

 

Regards,

 

Jim T.


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#37 JonNPR

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Posted 25 February 2016 - 02:17 PM

Thanks Jim. To complicate matters, the city works staff just replaced the old streetlight in our front yard with a bright new LED light. Now I'm not sure whether mild light pollution type filters designed for the prevalent older lights will be of any use. And I only recently bought the Lumicon, passing up a UHC.

 

I do have a DGM NPB and a Lumicon OIII. I have to believe these will require much longer exposers even with stacking, and that will be problematic with my SE mount.

 

Jon


Edited by JonNPR, 25 February 2016 - 02:20 PM.


#38 Astrojedi

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Posted 25 February 2016 - 05:56 PM

I use the Orion Skyglow imaging filter from my red/white zone and it works very well for most objects. Note that the transmission characteristics are the same as the IDAS LP filter.

 

Most LP filters will block out IR & UV (including the Baader, astrodon, IDAS among others) to improve contrast and avoid bloated stars.

 

The Lumicon Deep Sky seems to be an exception with regards to IR pass. I would look into that for galaxy imaging.


Edited by Astrojedi, 25 February 2016 - 05:57 PM.

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#39 JonNPR

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Posted 25 February 2016 - 08:18 PM

Jim, thanks for these terrific charts. 

Can you hazard a guess on how the advent of the bright, white LED street light conversions in many cities might affect the place of the various types of filters on your chart - or in general? Although the fixtures can be better designed for shielding, the dramatic increase in brightness, often with heavy degrees of blue end of the spectrum, is a big change. I have no idea what percentage street lighting makes up for overall city pollution. Any idea how this change is affecting filter performances? Narrowbands survive better? Broadbands suffer??

 

Before I buy any more filters I want to know a bit more. The City just replaced our old lights with new LEDs.

 

Thanks for any thoughts on this.

 

Jon

 

edit for spelling


Edited by JonNPR, 25 February 2016 - 08:19 PM.


#40 jimthompson

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Posted 26 February 2016 - 01:21 PM

I use the Orion Skyglow imaging filter from my red/white zone and it works very well for most objects. Note that the transmission characteristics are the same as the IDAS LP filter.

 

Most LP filters will block out IR & UV (including the Baader, astrodon, IDAS among others) to improve contrast and avoid bloated stars.

 

The Lumicon Deep Sky seems to be an exception with regards to IR pass. I would look into that for galaxy imaging.

Certainly filters designed specifically for "imaging" tend to have full UV and IR blocking built in, but many filters made for visual observing have reasonably good response to IR.  This is simply a matter of filter makers putting their money where it counts; we can't see IR with our eyes so there is no point investing in a filter that cuts it out.  The biggest discrepancy between filters that affects their suitability for use with EAA is how well they respond to Halpha at 656.3nm.  Again, since our eyes can't see this wavelength at night there is no particular need for the filter manufacturer to include good performance at that wavelength.  The filters that have risen to the top of the list for EAA are the ones that by coincidence have good response to Halpha and IR.

 

cheers,

 

Jim T.



#41 jimthompson

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Posted 26 February 2016 - 03:45 PM

...

Can you hazard a guess on how the advent of the bright, white LED street light conversions in many cities might affect the place of the various types of filters on your chart - or in general? Although the fixtures can be better designed for shielding, the dramatic increase in brightness, often with heavy degrees of blue end of the spectrum, is a big change. I have no idea what percentage street lighting makes up for overall city pollution. Any idea how this change is affecting filter performances? Narrowbands survive better? Broadbands suffer??...

 

Hi Jon,

 

Your question is a good one, and one that is becoming progressively more important as it seems that LED lighting has really become popular in new developments, and to a lesser but growing extent in existing municipalities.  I don't think anyone is really sure what the end result is going to be.  In theory with the more efficient lighting (LED's) comes more clever use of the light...full cut-off street lights, less light directed to the sky, etc.  However light intensity levels have increased, and as you mentioned the spectrum of the LED light is different than traditional outdoor lighting. 

 

I searched around online this afternoon and found what I could on outdoor LED lighting spectra.  The information readily available is not great, but seems to all consistently show the same general spectra: a broad band emission centered around 550nm (green) and a narrower band emission at 450nm (blue).  I've attached a graph that compares the typical LED spectrum with other sources of light pollution.  It appears that LED lighting is very similar to older man-made lighting except for the spike at 450nm.  This spike is what gives these lights the characteristic bright cool appearance.  If the spectrum I found can be trusted, the spike seems to be on the far side of Hbeta and O-III wavelengths, suggesting that our LP filters should still work okay.  Similarly the broader emission centered on 550nm seems to sit nicely between O-III and Halpha, so again we may be okay to keep using the LP filters we have.  The impact of LED lights would be more on broadband filters than narrowband.  I also would guess that we will have more difficulty observing reflection nebulae with LED lighting around since these nebulae have a strong blue component.

 

The problem of light pollution is not a simple one.  You have to consider not only the conditions locally (in your neighbourhood) but also the conditions around the city as a whole.  LP filters will be most effective dealing with the overall glow that the city casts on the sky.  In that regard I think outdoor LED lights are not prevalent enough to make a difference yet.  Locally though, such as street lights outside your house, I can see them being more of a problem.  My suggestion is to try to observe from a location that hides your telescope from local lights.  I have my scope setup in the backyard fairly close to the house so that the house blocks the street lights.  I also have a fair number of trees around the perimeter of my yard that effectively blocks other local outdoor lighting in the area.  This leaves only the general sky glow to deal with using filters.

 

cheers,

 

Jim T.

Attached Thumbnails

  • light pollution types.png
  • DSO types.png

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#42 JonNPR

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Posted 26 February 2016 - 07:52 PM

Thanks, Jim. Very helpful information, as always. My home observing location is in back of the house, and trees block much of the direct light from the LED. Some penetrates our front window "solar" backed Levalor shade AND sliding glass door's similar shade - by my scope. Neighbor imdoor lighting from two or three homes is a direct ambient source. So clearly not ideal! However the advent of EAA cameras and live stacking observing software like Starlite Live and AstroLive (and SharpCap and others?) may be more than compensating for these drawbacks. 

 

Jon

 

You probably saw these pages regarding LEDs and light pollution

http://www.flagstaff...ight-pollution/

http://www.techinsid...nasa-esa-2015-8



#43 ctc86

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Posted 28 February 2016 - 05:59 AM

Hello,

 

Long time lurker, first time poster here!

I have a Skywatcher light pollution filter. The only data I've found for it is the chart here: http://www.scopesnsk...erinchlpr .html. Is it any use for EAA? If the camera type matters, I have one of the DIY cameras (http://www.cloudynights.com/topic/488625-diy-camera-for-eaa-better-than-ln300/).

 

Cheers,

Chris



#44 Relativist

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Posted 28 February 2016 - 01:35 PM

There is what I use, and then there is my favorite.

I'd say my favorite light pollution filter is the one designed for the Celestron RASA, as it not only knocks down light pollution, but also is very well color balanced. This combination is very important to the majority of us that use OSC cameras. In fact, somewhat inadvertently I think Celestron and Astrodon have created the first LP filter that could be argued is ideal for EAA.

So far I have yet to find an equivalent in a 'normal' size. Eventually I may just purchase it and adapt it to the inside of my focuser on the 12".

If It were possible to creat a narrow band equivalent that uses a known pallet, like the Hubble, that would be a great thing for EAA as well as one could save/preprogram the color balance, and along with OSC cameras get close to the multi-filter results some get.

#45 jimthompson

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Posted 28 February 2016 - 08:49 PM

Hello,

 

Long time lurker, first time poster here!

I have a Skywatcher light pollution filter. The only data I've found for it is the chart here: http://www.scopesnsk...erinchlpr .html. Is it any use for EAA? If the camera type matters, I have one of the DIY cameras (http://www.cloudynights.com/topic/488625-diy-camera-for-eaa-better-than-ln300/).

 

Cheers,

Chris

Hi Chris,

 

I have tested the filter you are referring to along with a number of others sold by Skywatcher.  Skywatcher Canada sent me samples and asked me to test them and write a report, but the results belong to them so I can't share with everyone.  What I can say is that particular filter is not a light pollution filter.  I know it is advertised as one, and there are numerous other filter makers who sell the same filter and also call it a light pollution filter.  The truth is it does practically nothing to reduce light pollution.  It does however work very well for improving contrast on solar system objects like the Moon or Jupiter.  I have the version made by Baader called a Moon & Skyglow, and I use it fairly regularly on planets and sometimes on the Moon.  Never for deepsky objects.

 

Regards,

 

Jim T.



#46 jimthompson

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Posted 28 February 2016 - 09:02 PM

There is what I use, and then there is my favorite.

I'd say my favorite light pollution filter is the one designed for the Celestron RASA, as it not only knocks down light pollution, but also is very well color balanced. This combination is very important to the majority of us that use OSC cameras. In fact, somewhat inadvertently I think Celestron and Astrodon have created the first LP filter that could be argued is ideal for EAA.

So far I have yet to find an equivalent in a 'normal' size. Eventually I may just purchase it and adapt it to the inside of my focuser on the 12".

If It were possible to creat a narrow band equivalent that uses a known pallet, like the Hubble, that would be a great thing for EAA as well as one could save/preprogram the color balance, and along with OSC cameras get close to the multi-filter results some get.

Hi Curtis,

 

I was not aware of this particular filter, thanks for bringing it to my attention.  It looks like a similar approach to what Astro Hutech did with their IDAS LPS-P2 and Orion's  Skyglow Imaging filter.  I have the IDAS one, and indeed it gives a nice colour balance for objects such as M20 Trifid Nebula that has lots of blue in it due to the reflection nebula.  I have found however that all-in-all it is a poor performer due to the wide pass band around Hbeta-OIII, and the built in UV/IR cut that really hurts the view of galaxies.  My testing has shown something like the Astronomik UHC to be far superior at LP reduction.  To be honest I have not found the colour balance issue to be all that important, perhaps because I observe almost exclusively through a computer so there is lots of settings available to achieve the desired white balance.

 

Regards,

 

Jim T.

 

p.s.  That Celestron RASA filter is huge at 72mm diameter, and super expensive...$500 USD!



#47 ctc86

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Posted 29 February 2016 - 04:17 AM

Thanks for that, Jim. I've found two on your list that I can both find and afford - the Astronomik CLS and the Optolong UHC. Is there much difference between them? Which is preferable out of these two? More generally, what is the difference between UHC-type and CLS-type filters?

 

Cheers,

Chris


Edited by ctc86, 29 February 2016 - 11:59 AM.


#48 Relativist

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Posted 29 February 2016 - 04:59 AM

 

 

 

p.s.  That Celestron RASA filter is huge at 72mm diameter, and super expensive...$500 USD!

 

 

 

I'm not sure, the price per square mm looks good I think, maybe we could cut 3 or 4 smaller filters out of one? From what I've seen with the RASA it's well worth it IMO if you can swing one. Just like anything we do, some of it will be simply a difference in needing to fiddle with white balance, but some of it will be in what ultimately shows contrast. It'd be interesting to compare such multi-spectral filters + OSC vs a Mono + single band filters combined in software.



#49 jimthompson

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Posted 29 February 2016 - 03:16 PM

Hi Curtis,

 

I was curious so I scanned in the spectral response plot from the Celestron website for the RASA LPI filter, and ran it through my analysis.  I did the same for the IDAS LPS-D1 which I did not already have in my database (I had the older version the LPS-P2).  It would appear that the RASA LPI is a very close copy of the LPS-D1 filter, and so its performance is very similar (see attached plots).  Compared to other LP filters of the same overall brightness (% luminous transmissivity), these multi-band filters are poor performers.  Their only advantage is passing more blue, which is useful on targets with lots of blue like reflection nebulae.  In all other respects you are far better off with a more conventional LP filter like an Astronomik UHC, DGM NPB, Lumicon Deepsky, etc.

 

As for the cost, the Celestron RASA LPI is a rip-off.  If you were to buy the 72mm IDAS LPS-D1 the cost is only $329 USD compared to $499.95USD for the RASA LPI.  If you are looking for just a 1.25" or 2" version I would recommend the Optolong L-Pro which is even cheaper but performs slightly better than the IDAS filter.

 

On the topic of assessing LP filter performance on monochrome cameras, I did do one test with the aid of my friend Simon Hanmer and his monochrome Xtreme.  The brief summary report can be found here:

 

http://karmalimbo.co...s-27sep2014.pdf

 

The basic jyst being that LP filters are equally effective on monochrome cameras.  The observation above regarding multi-band filters versus normal bandpass filters was also demonstrated during this test.

 

Best Regards,

 

Jim T.

Attached Thumbnails

  • multiband_Feb2016.png

Attached Files



#50 jimthompson

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Posted 29 February 2016 - 03:50 PM

Thanks for that, Jim. I've found two on your list that I can both find and afford - the Astronomik CLS and the Optolong UHC. Is there much difference between them? Which is preferable out of these two? More generally, what is the difference between UHC-type and CLS-type filters?

 

Cheers,

Chris

Hi Chris,

 

Yes there is a noticeable difference between the Astronomik CLS and Optolong UHC.  The CLS has quite a bit wider a band pass around Hbeta and O-III, so it is not as effective at reducing light pollution as the UHC.  The contrast on nebulae will be noticeably better with the UHC.  The CLS however passes much more infrared, so it performs better on galaxies.  Thus they each have their strengths and weaknesses, so the decision on which to buy may need to be made based on something else.  Personally, I say choose the narrowest filter you can support with your exposure time (camera + mount tracking).  Even with an ALT-AZ mount, applying stack-on-the-fly software is opening up the use of narrower filters to more and more people as exposure time is becoming less of a concern.

 

As a general note, be careful when you read the names that manufacturers give their filters.  You can not necessarily compare UHC filters to each other or CLS filters to each other as there is no industry standard definition of what these terms mean.

 

Regards,

 

Jim T.




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