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Favorite Light Pollution Filter for EAA?

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#1 RafaelP

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Posted 01 October 2015 - 11:17 AM

Hello all!  It looks like I will have to upgrade my LP filter to a 2" to prevent some vingenetting from a 1.25".  I currently have a Baader Moon, Skyglow & IR filter, I haven't spent too much time with it to know how good it is.  

 

Since I will have to purchase a new LP filter, I wanted to know what your guys' favorite broadband filter for EAA is(especially for the extreme light pollution that I have to deal with in NYC.)  I posted this picture in my other thread, but I will put it here again, so you can get an idea of what it is like from my viewing area. 

ManhattanAstro

Thanks!

Rafael


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#2 jgraham

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Posted 01 October 2015 - 11:39 AM

The Baader's not bad. For EAA I prefer the Orion imaging skyglow filter or the Hutech IDAS LPS2.


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#3 Dwight J

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Posted 01 October 2015 - 11:44 AM

I use the Hutech as well.  My favourite is the Lumicon DeepSky filter.  If your vignetting is severe and these don't "cut" it, consider the Astronomics UHC.  



#4 Dragon Man

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Posted 01 October 2015 - 12:29 PM

I use the Hutech as well.  My favourite is the Lumicon DeepSky filter.  If your vignetting is severe and these don't "cut" it, consider the Astronomics UHC.  

Dwight, do you mean an Astronomics UHC or an Astronomiks UHC?



#5 Dwight J

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Posted 01 October 2015 - 12:32 PM

That would be with a "K"....herr Ken. The German -made one by Astronomiks.  And not the visual one.



#6 Dragon Man

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Posted 01 October 2015 - 12:46 PM

That would be with a "K"....herr Ken. The German -made one by Astronomiks.  And not the visual one.

:lol:  Danke Herr Dwight.



#7 mclewis1

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Posted 01 October 2015 - 01:11 PM

Rafael,

 

Because of your choice of camera and style of viewing (very short subs, live stacked) you cannot entirely take recommendations from the experience others have who use different cameras and styles of viewing (and possibly different light pollution). There is certainly a lot of value in those recommendations but you can't simply apply them entirely to your requirements. 

 

Look at color balance, transmission in the good areas of the spectrum, how restrictive the filter is to specific light pollution areas (and keep in mind your light pollution is likely changing as the use of LED lighting is increased).

 

The traditional guidelines for someone in your position is to go with the restrictive (but very effective) Astronomik UHC (and the brand is important because of some specific transmission characteristics) or narrow bandwidth Ha filter (7nm or smaller) for b/w work and extend your exposure times (requiring a reasonably good tracking eq mount).

 

In order to stay with shorter exposures (due to tracking issues and camera noise) you'll probably want to consider the filters with more transmission (Lumicon DeepSky or Orion SkyGlow Imaging or similar filters) but that's just a general idea.

 

On the whole you're really on your own when it comes to a specific recommendation ... simply because nobody else has experience with your combination of camera, style, scopes, and sky conditions.


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#8 Censustaker

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Posted 01 October 2015 - 02:11 PM

Take a look at Jim's article here: http://karmalimbo.co...onomy_part4.pdf

 

I recently tried out a Red #29 filter and got some good results on galaxies.


Edited by Censustaker, 01 October 2015 - 02:11 PM.


#9 jimthompson

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Posted 02 October 2015 - 04:43 PM

Hi Rafael,

 

I don't know if I fully agree with Mark's suggestion that specific recommendations can not be made unless we have the same camera, scope, sky conditions, etc.  I believe that in the case of filters there are some underlying principles that don't really vary much.  This stems from the fact that the objects we are trying to see emit light in very specific wavelengths, and those wavelengths don't change regardless of the equipment we are using to try and see them.

 

In my experience the basic underlying rule is:  to get the best contrast, use the narrowest filter that your mount tracking will support.  By your signature block it looks like you are working with the new ASI 224 camera and an EQ mount.  I'm guessing you are planning on stacking many short exposures?  For your location I'd recommend the Astronomik UHC.  You can observe galaxies and nebulae with this filter.  For added performance you can add your IR cut filter to the UHC.  Try that combo and see how it goes.  If you are wanting for more contrast, and your setup can support longer exposures per frame, then you can try Halpha filters for nebulae, and IR high pass filters for galaxies.

 

By the way, your Baader Moon and Skyglow is not really a light pollution filter.  It enhances contrast on planets and the Moon, but does virtually nothing to reduce light pollution compared to other filters.  You can read more about filters and how to choose them by checking out my Astronomy Technology Today magazine articles, especially Part 7 on choosing filters.

 

http://karmalimbo.co...ts/articles.htm

 

Regards,

 

Jim T.


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#10 mclewis1

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Posted 02 October 2015 - 06:49 PM

Jim,

 

I think you missed my "entirely" part  ... lol. I completely agree with you but I just didn't want Rafael to rely entirely on specific examples of what worked for others. He's doing something new and a little different and I was concerned that he'd look at what others had success with and assume that it applied entirely to his setup.

 

I really did want him to delve more into the understanding of and the selection process for the various filters.

 

What I'm curious about is with the restrictive nature of the UHC what happens to the short exposure subs with respect to camera noise? There's usually a "floor" below which the signal seems to get lost in the noise. The UHC is certainly allowing more good signal to be captured but it comes at the cost of needing longer exposures and that may or may not be something that makes sense to Rafael. 



#11 jimthompson

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Posted 03 October 2015 - 09:38 AM

I am curious as well Mark about the impact on very short exposures.  On one hand the net signal strength is lower, but on the other hand the signal to noise is better.  It will be interesting to see what the net result of adding an LP filter is to this reasonably recent method of imaging/NRT observing.  I know that adding LP filters to my video astronomy techniques has really expanded the capability.  I have high confidence that the same will be true with this new "rapid imaging".

 

cheers,

 

Jim T.



#12 RafaelP

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Posted 03 October 2015 - 10:07 AM

Thanks everyone for going over some of the issues.  

Ah, I thought the BaadeR Moon and Skyglow was a LP filter.  

 

I should have mentioned more about my set-up.  I have been using the ZWO ASI224 camera(after being inspired by Hinten's thread) and C5 with short exposures, usually 4-8 seconds.  I have the iOptron SmartEQ Pro, which is a lightweight GEM.  It may be possible to do much longer exposures, since I have not really used a LP filter yet the extreme skyglow pushes the histogram quickly to the right! 

Also, I am a bit confused about filtering out IR.  Is it something I want to do or not?

Perhaps I will try the DGM CGE filter to start with.  


Edited by RafaelP, 03 October 2015 - 10:13 AM.


#13 jimthompson

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Posted 03 October 2015 - 12:19 PM

Hi Rafael,

 

The Moon and Skyglow filter is sold by a number of different vendors, and in most cases it is marketed as a mild light pollution filter.  From my own testing and analysis this filter does almost nothing to improve the view of deepsky objects.  It does however work extremely well at improving colour intensity and contrast on planets and the Moon.

 

If you already have a DGM CGE filter, then it will work quite a bit better than your Moon & Skyglow to remove light pollution.  It is however pretty wide, ie. very mild LP reduction.  I think you will find that you need more LP reduction than what this filter provides.  Trying it will however give you an idea of what is possible and an idea of the impact on how you use the camera.

 

Regards,

 

Jim T.



#14 RafaelP

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Posted 03 October 2015 - 05:58 PM

Thanks Jim,

I don't have an LP filter yet.  I will peruse astromart to see what is available!

Thanks again,

Rafael



#15 Relativist

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Posted 04 October 2015 - 05:05 PM

I stack baader moon & skyglow and baader UHC. I'd encourage participation in light pollution societies, that's the best long term way to slow the impending issues, especially once LED lighting gets used.



#16 RafaelP

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Posted 04 October 2015 - 09:00 PM

I do have the DGM Optics NPB filter.  Is it really more for viewing nebulae?  Or  does it work well as a general narrowband filter?



#17 jimthompson

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Posted 05 October 2015 - 12:02 PM

Hi Rafael,

 

The DGM NPB should work fairly well on everything, but is best suited to nebulae.  My analysis suggests that it should perform similar to the Astronomic UHC, but I have not tested one myself to confirm.

 

cheers,

 

Jim T.



#18 Astrojedi

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Posted 05 October 2015 - 05:23 PM

I am curious as well Mark about the impact on very short exposures.  On one hand the net signal strength is lower, but on the other hand the signal to noise is better.  It will be interesting to see what the net result of adding an LP filter is to this reasonably recent method of imaging/NRT observing.  I know that adding LP filters to my video astronomy techniques has really expanded the capability.  I have high confidence that the same will be true with this new "rapid imaging".

 

cheers,

 

Jim T.

 

Jim, Rafael,

 

Below are some links to posts/images that illustrate short exposure stacking with the ASI224 using an Orion astrophotography light pollution filter (very similar spectral transmission as the IDAS LP filter but less expensive)

 

There was a significant improvement in SNR as I was able to push the gain higher at the same sub exposure duration or do longer sub exposures without the light pollution causing a whiteout (at my location I can usually only see stars brighter than mag 3).

 

I think a LP filter such as the Orion or the IDAS should work very well for Rafael.

 

http://www.cloudynig...-3#entry6799055

 

http://www.cloudynig...-2#entry6783655

 

http://www.cloudynig...-2#entry6783671

 

http://www.cloudynig...-2#entry6783680

 

http://www.cloudynig...27#entry6793668

 

http://www.cloudynig...26#entry6790884



#19 RafaelP

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Posted 06 October 2015 - 07:25 PM

Hi Hiten, 

I ended up purchasing the Orion Skyglow Imaging filter.  I think your images speak for themselves!  I will post results soon.

~R



#20 Astrojedi

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Posted 07 October 2015 - 09:50 AM

Best of luck. Also try a gain setting of 350 and 10-15s exposures with the filter otherwise you will leave money on the table so to speak :)

 

There are a few technical reasons for this but in short that's the point where the e/Adu conversation pulls the most signal out for short exposures. Works really well using the LP filter.



#21 RafaelP

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Posted 07 October 2015 - 06:18 PM

Hiten,
Thanks! What is e/Adu?
R

#22 Astrojedi

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Posted 07 October 2015 - 07:44 PM

e/Adu is the number of electrons per "Analog Data Unit" or in other words "gain". Below is a highly simplified mental model to understand this.

 

The ADU represents the quantization voltage. For example if a sensor lets say IMX224 outputs 2350mV (e.g. 1/30s accumulation as per Sony's website) and you have a 12bit ADC then each ADU will represent 0.57mv (2350/4096) for that exposure. ADUs are what get converted to bits by the ADC.

 

When you have very little signal then to maximize dynamic range you want to "spread" the accumulated electrons over as many ADUs as possible to maximize the dynamic range. So as you increase your gain the number of electrons per ADU (and voltage per ADU) falls and you improve dynamic range.

 

If you are doing longer exposures then you should reduce your gain as the sensor well will accumulate a lot more electrons so if your gain is too high you will lose dynamic range due to clipping. For very long exposures it is better to be closer to unity gain which is ~75 for this sensor. That will maximize dynamic range for the long exposure.

 

For stacking if you are doing 10-15s subs using a LP filter I find a gain of 350 to be the sweet spot. After that the "curve" starts to flatten out i.e. no further improvement in SNR as you hit the noise floor

 

Hope that helps


Edited by Astrojedi, 07 October 2015 - 08:30 PM.


#23 Live_Steam_Mad

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Posted 20 February 2016 - 02:25 PM

That would be with a "K"....herr Ken. The German -made one by Astronomiks.  And not the visual one.

 

If you mean that the one that you mention is not the visual Astronomik UHC, then which do you mean? I looked on the Astronomik website and there does not seem to be an Astronomik UHC which is stated as being for CCD use ;-

 

http://www.astronomi...uhc-filter.html

 

I see that the visual Astronomik UHC one can be used for CCD use, I have seen it used on NSN and it's impressive.

 

However, I looked at a "spectral picture" here ;-

 

http://www.tavcso.hu...z-tesztje_2.jpg

 

...and saw that the Castell UHC was almost seemingly identical, if probably not quite as high contrast, since it passes a slightly wider band, and at nearly 1/3 the price?

 

Since my Castell OIII 2" impressed me so much for visual use, I think I'll try the Castel UHC 1.25", it's only like 37 GBP! ;-

 

http://www.365astron...-Eyepieces.html

 

I really need a UHC or something since I am whiteing out with my LN300 camera when used past Brightness 10 and AGC low with C11 @F3 with my Light Pollution with no filters...

 

Regards,

 

Alistair G.



#24 Censustaker

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Posted 20 February 2016 - 02:30 PM

What exposure time are you using?

#25 Live_Steam_Mad

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Posted 20 February 2016 - 03:10 PM

What exposure time are you using?

 

Whoops, forgot that part. x32 worked fine, 3D-DNR 5, then Live Stacking in Sharpcap 2.7 and histogram tweak, worked great on M65 and M66, saw spiral arms. If I remember right, pretty sure that x64 and above whited out on me. I have ZLM 4.8 skies with averted vision, best nights, 23,500 street lights, I am 2 miles from Town Centre of 176,000 people and in the connurbation of Merseyside (about 3 million people). The clouds are bright orange.

 

Actually there's a thought, maybe I would need a different filter, I was trying to do galaxies. What's the best, most aggresive filter for galaxies in heavy Light Pollution (LP)?

 

My LN300 had it's internal IR filter removed so I would like to use an LP filter that transmits IR addition to the HB, OIII and Ha to aid picking up galaxies, especially since I have an ICX673 which is Ex-View 2 and 20 per cent more sensitive to IR than the Super HAD 2 e.g. ICX811 according to the Sony datasheet.

 

Best Regards,

 

Alistair G.


Edited by Live_Steam_Mad, 20 February 2016 - 03:13 PM.



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