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Best filter for galaxies in the city

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#1 skydivephil

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Posted 08 April 2021 - 08:38 PM

I Live in  Bortle class 9 inner city environment. I have a Celestron c8 and astro modified Sony a7s and would like to image galaxies. Would love to know what filters people recommend for this. We have Led street lights . Any tips most welcome. 

 

 



#2 Mr. Pepap

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Posted 08 April 2021 - 08:55 PM

Bortle 9 is simply no good for galaxies. Since they are so darn big, they have a low surface brightness compared to things like the Orion Nebula, famous for being extraordinarily bright.

 

You could try a UHC/LPR filter or an Oxygen-III Narrowband filter, but to get decent results, I always take a drive.

 

You don't have to go far. Even going to your local park can make a world of difference. Getting rid of things like overhead streetlights or lights from the neighbors' windows will help. Try to shoot for Bortle 4-6 to start (I find that helpful in my experience) or darker if you are willing to go there. There's nothing like a good road trip!

 

Hope this helps.


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#3 bobzeq25

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Posted 08 April 2021 - 08:56 PM

There is no magic filter for this.

 

The two strategies are.

 

More total imaging time.  More subs.

 

Gradient reduction in processing.  That uses a completely different strategy to target light pollution.   Light pollution is a gradient, most at the horizon, least overhead.  Computers can target that, and remove most of it.  It's not perfect, but it works on all targets, all sources of light pollution.    The gradient reduction method allows direct targeting of light pollution.

 

So-called "light pollution" filters don't magically know what light pollution is.  They're crude devices that whack out parts of the spectrum, on the hope that what they whack is mostly light pollution, what they pass, mostly signal.  For emission nebulae and metal vapor lights, that works pretty good.  For galaxies and LEDs - not so much.

 

Not my original thought.  Here's one good thread, there are others.

 

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

 

A coping strategy that some use in Bortle 9 is to limit their imaging to emission nebulae, using a mono camera and narrowband filters.  That is magic, it turns Bortle 9 into maybe Bortle 4.


Edited by bobzeq25, 08 April 2021 - 09:02 PM.

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#4 TOMDEY

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Posted 08 April 2021 - 11:36 PM

Unfortunately, there really is no filter that will help. You could attempt to image all night and only capture the equivalent of a few minutes of dark-sky data. It's really that bad. In that sense, the best filter is --- a tank full of gasoline.

 

Similar Challenges:

>roller-skating on a shag carpet

>juggling in a phone booth

>flying a kite on the moon

>texting while driving

 

Theoretically, all of those are possible... but not recommended.    Tom

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#5 GaryShaw

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Posted 09 April 2021 - 09:04 AM

Hi

Just to offer one very small, alternate and inconsequential opinion from a lowly EAA observer/imager, I live 2 miles west of downtown Boston - Bortle, 8-9, and have little difficulty coaxing decent images onto my screen and capturing them to enjoy later. 

 

Who wouldn’t love to live and observe/image in Bortle 3-4 conditions but, based on my humble experience, I have to believe that a patient and experienced AP guru, can coax decent Galaxy images out of a challenging skydome.

 

Of course, it’s all a matter of ‘expectations’ and acceptable ‘standards’ so I get why, for many AP folks, Bortle 8+ is  just a non-starter. Still, for those in urban locations and without the time or vehicle, the ‘full tank’ filter is not an option but the galaxies are still overhead challenging us to try.

 

Gary 

 

ps: Have any of you viewed the AP work of ‘Cluiv the Lazy Geek’ on his YouTube channel? He lives and creates beautiful AP images from inside urban Tokyo.  https://youtube.com/c/CuivTheLazyGeek
 


Edited by GaryShaw, 09 April 2021 - 09:07 AM.

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#6 BlueTrane2028

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Posted 09 April 2021 - 09:13 AM

Best filters for Bortle 9?

Air filter, oil filter, fuel filter and if your car is fancy, cabin filter.


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#7 jonnybravo0311

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Posted 09 April 2021 - 09:14 AM

Gary, it's certainly not impossible to image under absurdly light polluted skies. In fact, I typically point people to Cuiv's videos as proof. Also, the astronomy / astrophotography couple "Galactic Hunter" just recently did a video on imaging under light polluted skies. They live in Las Vegas.

 

The point being made here is there is no such thing as a magic filter. The "tank of gas" filter is a colloquialism to indicate the only way to get the dark sky is to drive out to an area with a dark sky. No matter how desperately filter manufacturers and retailers wish to convince you otherwise.


Edited by jonnybravo0311, 09 April 2021 - 09:22 AM.

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#8 gcardona

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Posted 09 April 2021 - 09:23 AM

While not ideal, take a look at my Astrobin to see my galactic images from Bortle 9 skies. The key is LOTS of integration time, usually 12-16 hours at least, over several days. It usually takes me 1 to 2 weeks to gather data for 1 image. No filters, except LRGB and Ha if appropriate.


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#9 GaryShaw

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Posted 09 April 2021 - 09:44 AM

Hi JB

Ok, I think I get that AP uses a variety of wide and narrow band filters to craft together amazing images and bring out the detail you’re interested in. Is there not some additional combination filters that you can use specifically to optimize contrast and cut through sub-optimal Bortle conditions?

 

Simple example: last night I had SQM 18.6 - don’t know how that translates to Bortle. I was trying to observe and sketch some of the faint irregular galaxies and star-forming regions from the article in the May S&T issue. Using my ASI294MC and applying master flat and dark, I was amazed when I cycled the filter wheel and positioned my Astronomik UHC filter. I can’t say it ‘popped into view’ - the object is too low in brightness and 12.3 magnitude, but it gave me enough hope that I kept coaxing it out with the histogram and ended with a decent view in my 15 minute observation. 
 

That’s just my simple ‘EAA observing within Bortle 8’ story but I have believed that AP has far more sophisticated procedures and crafty and skilled methods for applying multiple filters, creating multiple layered stacks of images made with different filters, which, taken as a whole, overcome challenging skies. 
 

However you guys do all that, I am still in awe.

Gary 


Edited by GaryShaw, 09 April 2021 - 09:46 AM.


#10 imtl

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Posted 09 April 2021 - 09:54 AM

Hi JB

Ok, I think I get that AP uses a variety of wide and narrow band filters to craft together amazing images and bring out the detail you’re interested in. Is there not some additional combination filters that you can use specifically to optimize contrast and cut through sub-optimal Bortle conditions?

 

Simple example: last night I had SQM 18.6 - don’t know how that translates to Bortle. I was trying to observe and sketch some of the faint irregular galaxies and star-forming regions from the article in the May S&T issue. Using my ASI294MC and applying master flat and dark, I was amazed when I cycled the filter wheel and positioned my Astronomik UHC filter. I can’t say it ‘popped into view’ - the object is too low in brightness and 12.3 magnitude, but it gave me enough hope that I kept coaxing it out with the histogram and ended with a decent view in my 15 minute observation. 
 

That’s just my simple ‘EAA observing within Bortle 8’ story but I have believed that AP has far more sophisticated procedures and crafty and skilled methods for applying multiple filters, creating multiple layered stacks of images made with different filters, which, taken as a whole, overcome challenging skies. 
 

However you guys do all that, I am still in awe.

Gary 

Gary, I think the answer is more or less "what do you want your image to look like" or "what do you want to see in your image" approach. You will get an image of a galaxy with different filters, however, it will lack details, depth, and will be color skewed and that is due to the nature of broadband objects and of these filters. Is it worth it? up to you to decide.

 

"just to spot a galaxy" with a filter in is not really AP territory as you said. It's more of a visual/maybe EAA things. And it's great, don't get me wrong. Different hobbies as far as I'm concerned.



#11 Jared

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Posted 09 April 2021 - 10:57 AM

There are no magic filters that will help, but don’t get too discouraged. Stick with moderately bright or showcase type objects and get plenty of integration time and you can get really satisfactory results. They will never be as deep as those captured from darker skies, but it’s not like you can’t get something that will make you happy.

 

Here is one I took a little over a week ago (during a full moon, no less). Bortle 9 here in Oakland, CA. Neighbor’s lights on all night. Street light only partially blocked by the front of the house. Bad light pollution gradients. 

 

JSW2027767.jpg


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#12 jonnybravo0311

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Posted 09 April 2021 - 10:59 AM

Hi JB

Ok, I think I get that AP uses a variety of wide and narrow band filters to craft together amazing images and bring out the detail you’re interested in. Is there not some additional combination filters that you can use specifically to optimize contrast and cut through sub-optimal Bortle conditions?

 

Simple example: last night I had SQM 18.6 - don’t know how that translates to Bortle. I was trying to observe and sketch some of the faint irregular galaxies and star-forming regions from the article in the May S&T issue. Using my ASI294MC and applying master flat and dark, I was amazed when I cycled the filter wheel and positioned my Astronomik UHC filter. I can’t say it ‘popped into view’ - the object is too low in brightness and 12.3 magnitude, but it gave me enough hope that I kept coaxing it out with the histogram and ended with a decent view in my 15 minute observation. 
 

That’s just my simple ‘EAA observing within Bortle 8’ story but I have believed that AP has far more sophisticated procedures and crafty and skilled methods for applying multiple filters, creating multiple layered stacks of images made with different filters, which, taken as a whole, overcome challenging skies. 
 

However you guys do all that, I am still in awe.

Gary 

We do go to some rather insane lengths to obtain photons :). For example, the post by Gabe right before yours shows that at a MINIMUM he acquires 12-16 hours of data and spends 1-2 weeks acquiring that data before he considers it to be enough for an acceptable image.

 

A lot of imagers who suffer from terrible light pollution (Bortle 8/9, so, SQM under 18-ish) go for narrowband imaging of emission nebulae. These are "easier" because for those targets the filters _are_ magic. This is where a filter like the Optolong L-eXtreme or Radian Triad Ultra shines in conjunction with a color camera. Or, if you've got a camera with a mono sensor, dedicated S2, Ha and O3 filters allow you to gleefully ignore the fact that you can read a book outside at night.

 

Unfortunately, for broadband targets like galaxies and clusters, those filters don't work. I'll use my rainbow analogy here. If you were to take a picture of the rainbow, you'd expect your image to look like a rainbow with red, orange, yellow, green, etc. Put one of those light pollution filters on your camera and take another picture of the rainbow. The result will be missing some purples, some blues and have nearly all the oranges and yellows stripped out. Funny looking rainbow, right? That's what light pollution filters do. They whack out swaths of the spectrum. Unfortunately, the galaxies and clusters are the "rainbows", so by using the LP filter, you're skewing the colors of the galaxies, stars and clusters. Whether _you_ find that skewing acceptable... well... I can't answer that one :).


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#13 rj144

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Posted 09 April 2021 - 11:16 AM

There are no magic filters that will help, but don’t get too discouraged. Stick with moderately bright or showcase type objects and get plenty of integration time and you can get really satisfactory results. They will never be as deep as those captured from darker skies, but it’s not like you can’t get something that will make you happy.

 

Here is one I took a little over a week ago (during a full moon, no less). Bortle 9 here in Oakland, CA. Neighbor’s lights on all night. Street light only partially blocked by the front of the house. Bad light pollution gradients. 

 

attachicon.gifJSW2027767.jpg

Great photo!



#14 skydivephil

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Posted 09 April 2021 - 11:20 AM

There are no magic filters that will help, but don’t get too discouraged. Stick with moderately bright or showcase type objects and get plenty of integration time and you can get really satisfactory results. They will never be as deep as those captured from darker skies, but it’s not like you can’t get something that will make you happy.

 

Here is one I took a little over a week ago (during a full moon, no less). Bortle 9 here in Oakland, CA. Neighbor’s lights on all night. Street light only partially blocked by the front of the house. Bad light pollution gradients. 

 

attachicon.gifJSW2027767.jpg

that picture is amazing , did you use any filters at all?



#15 klaussius

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Posted 09 April 2021 - 11:22 AM

Unfortunately, there really is no filter that will help. You could attempt to image all night and only capture the equivalent of a few minutes of dark-sky data. It's really that bad. In that sense, the best filter is --- a tank full of gasoline.

This is so very true.

 

But if taking a trip to a dark sky isn't an option, some filters may help a bit.

 

I recently put the Orion 5561 skyglow imaging filter to the test, it's in design very similar to an L-Pro or an IDAS LPS D2. It provides a decent SNR boost, and doesn't hurt colors or signal too much.

 

That said, the improvement is not dramatic, and a tank full of gas would handily beat the filter. It's just that the filter is way more convenient for those of us stuck imaging at home for whatever reason.

 

YMMV in any case, depending on your car make and model, and your sky conditions. In my case, my city is full of LED street lights, which is the worst case for such filters.


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#16 Jared

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Posted 09 April 2021 - 11:27 AM

that picture is amazing , did you use any filters at all?

It is a monochrome camera, so LRGB filters. That’s it. The rest is just integration time. I believe I had about ten hours of luminance data for that one. Necessary because of the heavy light pollution. If I were somewhere dark, I could do that in a single night. From my back yard? That’s three nights of data, and the color info is pretty weak—it could benefit a lot from some additional RG&B. 

 

I would consider myself a more experienced imager, so I’m not saying anyone can get this with 50mm RedCat from Times Square, but I wouldn’t want people thinking Bortle 9 is hopeless. It just adds a different challenge. Under light polluted skies you really DO need a lot of integration time, though. Don’t expect multiple broadband targets per night if you want a frame worthy picture. Rather, expect multiple nights per target. 

 

My SQM for these nights, by the way, was in the 13’s. Really, really bad. 


Edited by Jared, 09 April 2021 - 11:28 AM.

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#17 skydivephil

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Posted 09 April 2021 - 11:28 AM

This is an image of M81 using my c8 with hyperstar, zw0 1600 colour and IDAS nb1 filter I understand that galaxies are broadband emitters , but there is an issue with skyglow that I believe can be attacked with filers that aren't too narrow. So i think people are being too pessimistic here :

https://www.flickr.c...57711024815906/

Sure id love to go out to a dark sky site but due to Covid restrictions this isn't possible. And when they are lifted soon, all the Air BNB in dark sky locations will be booked up solid. So for now Im stuck in the city and trying to make the most of it. 


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#18 imtl

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Posted 09 April 2021 - 11:30 AM

This is an image of M81 using my c8 with hyperstar, zw0 1600 colour and IDAS nb1 filter I understand that galaxies are broadband emitters , but there is an issue with skyglow that I believe can be attacked with filers that aren't too narrow. So i think people are being too pessimistic here :

https://www.flickr.c...57711024815906/

Sure id love to go out to a dark sky site but due to Covid restrictions this isn't possible. And when they are lifted soon, all the Air BNB in dark sky locations will be booked up solid. So for now Im stuck in the city and trying to make the most of it. 

If you are happy with your results then that's all that matters.



#19 imtl

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Posted 09 April 2021 - 11:31 AM

It is a monochrome camera, so LRGB filters. That’s it. The rest is just integration time. I believe I had about ten hours of luminance data for that one. Necessary because of the heavy light pollution. If I were somewhere dark, I could do that in a single night. From my back yard? That’s three nights of data, and the color info is pretty weak—it could benefit a lot from some additional RG&B. 

 

I would consider myself a more experienced imager, so I’m not saying anyone can get this with 50mm RedCat from Times Square, but I wouldn’t want people thinking Bortle 9 is hopeless. It just adds a different challenge. Under light polluted skies you really DO need a lot of integration time, though. Don’t expect multiple broadband targets per night if you want a frame worthy picture. Rather, expect multiple nights per target. 

 

My SQM for these nights, by the way, was in the 13’s. Really, really bad. 

13?!?!?

blast.jpg


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#20 GaryShaw

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Posted 09 April 2021 - 11:47 AM

13?!?!?

attachicon.gifblast.jpg

I did not know that the SQM meter registered that low...! I only hear from folks elsewhere that they had a disappointing night with SQM at 19.5 or 20.5....instead of 21.

 

I'd be happier by the realization that I don't have it that bad except that I fear that we are all heading towards SQM of 13 and skies full to Skylink satellite trains - ugh!

Gary



#21 jonnybravo0311

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Posted 09 April 2021 - 11:54 AM

It is a monochrome camera, so LRGB filters. That’s it. The rest is just integration time. I believe I had about ten hours of luminance data for that one. Necessary because of the heavy light pollution. If I were somewhere dark, I could do that in a single night. From my back yard? That’s three nights of data, and the color info is pretty weak—it could benefit a lot from some additional RG&B. 

 

I would consider myself a more experienced imager, so I’m not saying anyone can get this with 50mm RedCat from Times Square, but I wouldn’t want people thinking Bortle 9 is hopeless. It just adds a different challenge. Under light polluted skies you really DO need a lot of integration time, though. Don’t expect multiple broadband targets per night if you want a frame worthy picture. Rather, expect multiple nights per target. 

 

My SQM for these nights, by the way, was in the 13’s. Really, really bad. 

So... it was you in Times Square with the RedCat, then. Wait... you're in Oakland... you imaging from the Coliseum outfield during games? :p

 

In all seriousness, that's a heck of a nice image of the Whirlpool.



#22 WadeH237

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Posted 09 April 2021 - 12:46 PM

Is there not some additional combination filters that you can use specifically to optimize contrast and cut through sub-optimal Bortle conditions?

For emission nebulae?  Yes!  Absolutely.  Narrow band filters are very effective here.

 

For galaxies?  Not so much.  I know that not everyone agrees with me, but in my opinion, the best way to capture galaxies is with zero filters (except IR and UV, and RGB if using a mono camera).

 

The issue is this:

 

Filters only block light.  100% of filters ever made have the effect of reducing the number of photons that reach the sensor.  If you can block unwanted light, while letting most of the wanted light through, that's a worthwhile thing.  Yes, you are blocking some of the desired light, but you are blocking the unwanted light even more.  This increases contrast in the image, which is a good thing.

 

With emission nebulae, you want only the specific wavelengths that are emitted by the gasses that make up the nebula.  You can relentlessly block the other 99% of the spectrum.  That is what narrow band filters do, and it's even effective with moonlight.

 

With pre-LED lighting, much of the light pollution was produced by a few specific types of lamps that emit in known, discrete wavelengths.  So classic light pollution filters allow the bulk of light through, but block those specific light pollution frequencies.  These filters don't help with moonlight, since moonlight is just reflected sunlight, which is full spectrum.  LED lighting is also full spectrum, so it cannot be selectively targeted and blocked by a filter.

 

Galaxies are full spectrum emitters, so any filter will block important light from them.  Perhaps another way to put it is that, in terms of spectrum, LED lighting, moonlight and the light from galaxies are all comprised of the entire spectrum.  As such, they "look" very much like each other.  Any filter that blocks one of them, will block all of them.

 

None of this means that you can't image galaxies under light pollution.  It just means that you need much more exposure time (like the 1 to 2 weeks for a single target mention above).  And it means that you will be dealing with gradients, and possibly reflections, when you process the data.  My suggestion is to stick with the brightest galaxies - and don't use any filters.  Gather as many photons as you can, as fast as you can.


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#23 Jared

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Posted 09 April 2021 - 05:33 PM

13?!?!?

attachicon.gifblast.jpg

Yeah, thirteen point something. Most nights I run seventeen point something (depending on my neighbor's inside lights--it's a city and his den is only a few feet from my telescope. The street light out front is a bit farther away, but no more than sixty or seventy feet in total and very poorly shielded. Just past full moon as well for much of the data in that image. On a really dark night (for my neighborhood) I will get to maybe 17.8 magnitudes per square arc second, but that's literally the best I can do from home, and even that is pretty firmly Bortle 9. Let's just say, I can a bad night I can't see Megrez at magnitude 3.3. It's not quite the Las Vegas strip, but it's really bad.



#24 Jared

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Posted 09 April 2021 - 05:36 PM

I did not know that the SQM meter registered that low...! I only hear from folks elsewhere that they had a disappointing night with SQM at 19.5 or 20.5....instead of 21.

 

I'd be happier by the realization that I don't have it that bad except that I fear that we are all heading towards SQM of 13 and skies full to Skylink satellite trains - ugh!

Gary

Yeah, 13 is as bad as it gets for me. The best nights are in the 17's. I don't think I have ever touched 18 from home. I did have an observatory till last summer under Bortle 4 skies, but it burned down in the fires. I salvaged all the equipment, but the solar panels and everything that runs the observatory itself is toast. Haven't decided whether to rebuild it or not yet--it's about the fifth year in the last seven that it's been threatened by fire, and this year it happened. So for now the equipment is all at home. That's not too bad, though... It's letting me perfect all the automation, collimation, and tweaking that I never got to when the equipment was remote. Now, if I do rebuild the observatory, I'll be able to get a lot more out of it.



#25 Jared

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Posted 09 April 2021 - 05:41 PM

So... it was you in Times Square with the RedCat, then. Wait... you're in Oakland... you imaging from the Coliseum outfield during games? tongue2.gif

 

In all seriousness, that's a heck of a nice image of the Whirlpool.

It's not the Coliseum, but it feels like it sometimes. There is a street light in my front yard--literally twenty feet from the house--that is bright enough that my kids couldn't sleep till we put in black-out curtains for them. The house blocks the worst of it (along with most of the eastern and southern skies), but if there is any moisture in the air the light just gets scattered all over the place. Then there's the matter of my neighbor's den... No curtains, and he leaves the light on all night more often than not. That's about twenty feet from the telescope towards the north. 

 

I treat it all as a challenge! Just what is possible under really bad light pollution?

 

Next step will be figuring out how to image from a rowboat. 




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