Any tips for imaging under heavy light pollution? Suburban Astrophotography · Chris Sullivan · ... · 57 · 1509 · 4

Chris-PA 3.31
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Hi everyone - I image from a heavily light-polluted area outside of Philadelphia, PA and have little to no chance of imaging elsewhere. I recently tried to go after NGC 1333 - a reflection nebula with some dark dust around it and it was a total failure. The dark portions looked more like terrible gradient/vignetting than anything else (I ultimately just cropped it all out).  The reflection portion lacked any definition and my attempts to brighten it while leaving the sky dark just led to a total loss in definition. I use the Orion Skyglow Astrophotography filter and it has worked very well for me, but it definitely has its strengths and weaknesses (as does my camera). Are objects like dimmer reflection nebulae just out of reach for us or are their other tactics we can use?
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msoutham 1.20
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Hi Chris,

Defiantly recommend reading up on narrowband astro-photography. Have a look at this thread on cloudy nights.

http://www.cloudynights.com/topic/504951-astrophotography-in-light-pollution/
Edited ...
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Slawomir 0.00
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Hi Chris, Michael's suggestion is very good. From my experience, forget any sky glow filters and get the narrowest quality filters you can buy (3nm are gold in extremely light polluted sites), and when combined with a mono camera you will be amazed with the amount of detail you will be able to pick up. I'm talking of emission nebulae of course.
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Chris-PA 3.31
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Right - I'm not sure I can afford 3 nm filters, unfortunately (don't even have a monochrome camera just yet) - I've seen some 7 nm  filters I might be able to afford in the near(ish) future, but in all honesty, I'm a little more interested in galaxies than nebulae. Am I just out of luck or are there any secret tips or tricks for getting the detail I crave with the light pollution I live under?
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Slawomir 0.00
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·  1 like
To my limited understanding, DSO signal that is buried in the noise from sky glow is pretty much lost, or at least very difficult to recover. LOTS of sky limited subs, perfect guiding and good flats will be essential in taking photos of galaxies from a heavily sky polluted site, or actually from any site I would personally stay away from cheap filters - maybe try Astronomik or similar? Filters in astro are like spark plugs in a car...without the good ones the rest won't work to the full capacity.
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Chris-PA 3.31
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Hmm... I understand what you're saying, but 7 nm means I can try my hand at narrow band imaging. The prices for 3 nm - 5 nm filters simply puts that out of reach for me. :/
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Slawomir 0.00
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I know what you mean. I acquired mine over time, one by one. I think Astronomik now makes 6nm ones?
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craig_rodgers 0.00
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Chris Sullivan:
Hmm... I understand what you're saying, but 7 nm means I can try my hand at narrow band imaging. The prices for 3 nm - 5 nm filters simply puts that out of reach for me. :/


I agree, I went with Baader's for that reason and am starting to get pretty good results from my back garden. Still working out the processing though...The Astrodons have an astronomical price tag ;)
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Chris-PA 3.31
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Yeah, but even those are $200 more (for a set of three) than the 7 nm filters I was looking at.
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KuriousGeorge 1.20
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Chris Sullivan:
Hi everyone - I image from a heavily light-polluted area outside of Philadelphia, PA and have little to no chance of imaging elsewhere. I recently tried to go after NGC 1333 - a reflection nebula with some dark dust around it and it was a total failure. The dark portions looked more like terrible gradient/vignetting than anything else (I ultimately just cropped it all out).  The reflection portion lacked any definition and my attempts to brighten it while leaving the sky dark just led to a total loss in definition. I use the Orion Skyglow Astrophotography filter and it has worked very well for me, but it definitely has its strengths and weaknesses (as does my camera). Are objects like dimmer reflection nebulae just out of reach for us or are their other tactics we can use?


Can you send me your data for NGC1333? I may be able to make a recommendation. I cannot see the milk way and only see a few dozen stars.
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alocky 0.00
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I have my scope setup only a few km from the centre of a city of over 2 million people. I've found that it's possible to go quite deep with long integration times, and fast optics. Tools like pixinisght's DBE are extremely valuable for removing the light pollution gradient. The thinking behind the advantage of faster optics means you record a smoother image of the light pollution too, which makes subtracting it more effective. I've managed to image some pretty faint galaxy extensions from my location with only a 10"f4.5. Of course, it is never as good as a dark site, but my main problems come from stray light scattering into my optical train, rather than the background glow.
cheers,
Andrew.
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Chris-PA 3.31
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Can you send me your data for NGC1333? I may be able to make a recommendation. I cannot see the milk way and only see a few dozen stars.


It won't be finished uploading until another 15-20 minutes (around 2:05 p.m. EST), but here's a link: https://www.dropbox.com/sh/5cp8xvqsvw25jfa/AABC0afQJgOZXe8GQTFpYlEPa?dl=0

It might actually be that my flat frames failed, but I can't figure out why - histogram was right around 50%, I had a white t-shirt over the scope , I took them the morning after and did not touch my focuser or anything. I'm not sure what else I could have done (or what I could have done wrong).
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Chris-PA 3.31
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Andrew Lockwood:
I have my scope setup only a few km from the centre of a city of over 2 million people. I've found that it's possible to go quite deep with long integration times, and fast optics. Tools like pixinisght's DBE are extremely valuable for removing the light pollution gradient. The thinking behind the advantage of faster optics means you record a smoother image of the light pollution too, which makes subtracting it more effective. I've managed to image some pretty faint galaxy extensions from my location with only a 10"f4.5. Of course, it is never as good as a dark site, but my main problems come from stray light scattering into my optical train, rather than the background glow.cheers,
Andrew.

I've been resisting it so far, but I think Pixinsight is definitely in my near future. Like I alluded to above, I'm hoping to switch to a monochrome camera, and I think I'm going to need PI to process different channels through it, so I've been waiting to see if I can finagle an MC camera as a combined Christmas/birthday gift from the Mrs. before using my free trial. So far, I've been making due with DSS and CS2 (both of which are free).

I've got a fast scope - an f/3.9 Newtonian. With regard to stray light: I'm also definitely considering flocking - my scope came with a defective secondary spider that I've been able to make work with hand adjustments and REALLY tightening everything down. The maker has designed a new version of the spider, which should be shipping to me any day now. Since I have to switch that out, I might as well flock, right?

But when I was still doing DSLR imaging and before I had my skyglow filter, I couldn't even hit 5 minute exposures without a bright pink / nearly white sky. How do you manage to go deep without going white?
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Krizan 5.73
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Hi Chris, I live in Allentown.  Not as polluted as Philly, but still bad.  I am surrounded by warehouses lit  up all night long.

Narrow band is your answer (buy used).   I am for the most part restricted to it.  A fast scope will increase the Single/Noise ratio.  So, you are good there.  The problem becomes backfocus, with reflectors, when using a filter wheel.  I feel One Shot Color is very difficult, if not impossible in light polluted sites.  They really need dark skies.  I am also partial to low noise Sony chips with high QE.   I use the Starlight Xpress SX694.

I have been doing AstroPhoto for about 10 years, and one thing I have concluded, is most on the instruction/guidelines assume you have a dark site.  Imaging in light pollution is a whole other game.

I image with Astronomics 12nm Ha-OIII-SII filters.  One of the reasons I am restricted to 12nm is I use the Hyperstar F2 system.  The wide angle of F2 restricts the narrowness of the filter.  I have a very limited field of view from my backyard, and imaging time is limited,  so short sub frames are a must.  However, I just but in a POD.  Which will allow me to do multi nights on a DSO object.  I may move to 3nm filters.

Considering cost and your desire to image galaxies, you might consider traveling.  I am a member of LVAAS (Lehigh Valley Amateur Astronomical  Society). The club has two sites.  One at South Mt. (north of Bethlehem - not very dark) and a second at Pulpit Rock on the apalachey trail ( not real dark, but the Milky Way is visible).  In Pennsylvania our best shot is Cherry Springs State Park ( a dark site park supported by the state park system).  It is mowed with electric boxes throughout the field.  WiFi and flush toilets  There are also observatories you can rent, but no scope/mount in them, just a lockable shelter ( only for a few nights).   But those alternative are, for the most part, only useable in the warmer months.

If you check out my image of the Tulip (  http://www.astrobin.com/122253/?nc=user  ) you can get some idea what can be done from a polluted site using narrow band filters and a fast system.  For that image I only used Ha & OIII.  I created a synthetic green in Photoshop.  By the way PS2 should do you for awhile.

Lynn
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KuriousGeorge 1.20
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Chris Sullivan:
Can you send me your data for NGC1333? I may be able to make a recommendation. I cannot see the milk way and only see a few dozen stars.
It won't be finished uploading until another 15-20 minutes (around 2:05 p.m. EST), but here's a link: https://www.dropbox.com/sh/5cp8xvqsvw25jfa/AABC0afQJgOZXe8GQTFpYlEPa?dl=0

It might actually be that my flat frames failed, but I can't figure out why - histogram was right around 50%, I had a white t-shirt over the scope , I took them the morning after and did not touch my focuser or anything. I'm not sure what else I could have done (or what I could have done wrong).

Thanks for the data. Your site has potential IMHO...

http://www.astrobin.com/271982/B/
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Chris-PA 3.31
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Thanks for the data. Your site has potential IMHO…


Thanks for the attempt at processing!! I really appreciate it and those are some great recommendations. I'm going to have to look into making a lightbox on my own - I don't think I could afford one.

About the bias frames: I've never completely understood my camera's offset settings. I can easily take the darker bias frames by turning the offset and gain down to 0 (including the RGB levels), but wouldn't that mess up the calibration? I've come to learn that without an offset setting of at least 10, a subframe will stay nearly black even after a five minute exposure. What would you recommend as settings for the bias frames then? At any rate, due to light leak around the crayford focuser, I actually keep the inside of the focuser (right above the secondary) covered with my guide scope's cover (they're both exactly 50 mm so no light can enter) when taking bias, darks and dark flat frames.

How come I should do flats at night? Is that for focus shift? I have a carbon fiber tube that's less susceptible to focus shifting (albeit not immune, of course). It's weird - sometimes my flat frames will work perfectly and other times, they'll fail miserably without changing a thing.

My tracking is generally good thanks to good guiding, but I'm still working on my polar alignment. I don't have enough of a sky to work with for drift alignment, so I'm going to get a PoleMaster soon (hopefully). My wife's going to kill me...

I think once I do get a PoleMaster, doing 12+ hour subs will get easier. I'll be able to start once the sun goes down (a perk of working from home). Right now, my best option for polar aligning is the all star polar alignment routine via my mount's control pad (annoying when I'm plate solving). So I do a two-star align, polar align, two-star align, polar align, etc. until it doesn't slew during the polar alignment. It takes way too long and it's not good enough - it stops slewing for adjustments around 1 arc minute. I tried SharpCap's polar alignment feature for a while and that really messed me up - I figured out it was because my guide scope wasn't 100% parallel with the mount - that's a tough adjustment to make when you're concentrating on tightening everything down to avoid flex. Anyway, right now, I'm mostly limited to 3 hours on any subject as my sky isn't free of trees (by a long shot). You'll notice that nearly all my subjects are in the same general area of sky...

Again - thanks for your processing and suggestions. I'm really hoping that LRGB imaging works for me, because I really am more interested in galaxies than nebulae - the latter may look prettier, but conceptually, galaxies have fascinated me far more.
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Chris-PA 3.31
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Hi Lynn,

I should be okay with backfocus - on the one hand, I use a focuser extension tube because of my coma corrector, on the other hand, I have a set of T2 extension rings between the coma corrector and my current camera. If I switch to a monochrome camera and filter wheel, then I just get rid of one of the rings or use a different one and should be fine. I'd really love to go CCD and was thinking about a KAF8300 model. I know - Sony makes less noisy chips than Kodak, but I have to admit: even a KAF camera is out of any conceivable budget. I was talking to another imager that has an Atik and the ZWO ASI1600MM and she swears that is just as low noise as her Atik 460EX even though it's a CMOS. Since that's truly the only monochrome camera I can afford (and I really want the larger sensor size - I'm using a Sony Exmor-equipped QHY right now and there are so many objects that don't fit on my sensor that would fit on a micro 4/3 size sensor), it's really that or nothing. They're releasing a package with an 8 position filter wheel and LGRB+narrow band 1.25" filters for $1999. My wife is going to be livid, but not as much as if I were asking for a QSI, Atik One, Moravian or god forbid an SBIG (PLUS the price of 7 filters!).

So you use 12 nm filters because of the hyperstar (it's funny - I actually just read something about an imager from SW PA using 3 nm filters on a hyperstar system and getting better results than with wider narrow band filters) - knowing that I probably will get 7nm regardless, in your opinion, would doing so be a mistake? It's kind of my only option at this point in time. :/

Traveling is very hard - I have a 2 and 4 year old at home. When I first started out, I'd drive 20 minutes to my parents' place since they don't have street lights where they live. I think it helped, but I wouldn't be able to get started around 10:00 p.m. and would end up driving home dead tired at 2:00 a.m. I'm honestly glad that's over. As I'm self-employed, I often work late into the night as well, so I'd miss out on a lot of clear nights if I were traveling. In the future, I'd love to take the family to Cherry Springs a few times a year, but for now - I think I'm stuck on my roof.

Is it possible to integrate the different channels with Photoshop CS2? I feel like I'm going to eventually switch to PixInsight and since I don't know CS2 inside and out just yet, I feel like it'd be smarter to make the move sooner rather than later. Besides, this Exmor chip is actually kind of noisy, I'd love to try those noise reduction routines in PixInsight and see what I can get out of it. Thanks for your input, by the way!
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KuriousGeorge 1.20
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Hey Chris...

1.  Bias should be taken with the same settings you're imaging at. I get the feeling you're having light leakage. Maybe just cover the entire setup with a canvas while doing bias, darks and dark flats?

2. With you light pollution, flats will be super important. I always do them at night with http://www.optecinc.com/astronomy/catalog/alnitak/flatman.htm. With your vignetting, I suspect light leakage is getting into all of your images (lights, darks, flats, bias).

3. I see the non-round stars. I was guessing a focus or tracking error, but it could be due to poor polar align.

4. I like PHD for polar align. I just turn off dec correction while guiding and adjust my Az & El until no more dec drift. A pier will really help in your situation. When you go to LRGB, your might need 20+ hours for an object.
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Krizan 5.73
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Hi Chris, I don't know much about the optical physics behind bandwidth and F stop angles.  But my understanding is the light comes in fairly directly in the center of the field.  But it becomes very angled as it approaches the outer field.  Therefor it is hitting the filter glass at a more extreme angle and going through more glass. I'm not sure if that causes light fall off or what.  Baader make narrowband Highspeed filters for fast scope to F2.  The glass of the filters are figured so it is thinner as it approaches the edge.  The 1.25 set is $650 but the 2" is $389 each.    I would really have to continue to be very committed to Hyperstar and hear great things about them to put out that $1000.   The F2 angle of the Hyperstar needs 2" filters even for my chip.

There are different ways to bring narrow band data into Photoshop.  CS2 should do that as well as 6.  I use 5 now, but used 2 for years.   I use Maxim v6 to stack/combine.  It combines the Ha,OIII & SII into an RGB.  It allows me to choose what color band width I want each filter to be and allows me to weight each filter.  I just did that today for an image of the Bubble.

When it comes to CCD cameras, I adopt the fine refractor approach.  Quality over size and always try to buy used first.

Lynn
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bobzeq25 0.00
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I image DSOs in my suburban backyard, mid 18s mag per arc sec, Bortle 7.  Have done just a little narrowband, likely to do more, it's just too good.

With wideband, the first thing to work on is gradient reduction in processing.  It comes before light pollution filters, in my opinion.

What light source are you using for your flats?  After trying a number if things, I think the spike-a-flat panel is the easiest, best thing I've found.  I don't bother with t-shirts with it, I think they might just mess up the uniformity.
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peleks 0.00
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well i use baader UHC-S luminance booster, works fine even under full moon!
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Chris-PA 3.31
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KuriousGeorge:

1. I do have light leak from around my focuser (between the focus tube and around the crayford mechanism) - is there a good way to block that without affecting the functionality of the focuser (I feel like a “pouch” with two openings and two drawstrings would be ideal)? Do others have this problem? Like I mentioned above, I take darks, dark flats and bias frames with the cap of my guide scope over the inside of the focuser tube and I know it blocks all light when doing the calibration frames - five minute darks with my scope’s cover on taken the next day would come out white until I figured out where the light leak was coming from. If I still had light leak during the bias frames, I’d know when taking the darks, so the only consequential light leak I’m still suffering from is when taking light frames.

2. Yikes - that flatbox is outside my current (and foreseeable) budget. I did find a site a while back where someone had built one and shared instructions on how to do that. I’m going to have to look into it again.

3. There are two things contributing to my non-round stars, but the primary one is probably bad polar alignment. I did try PHD2’s alignment routine once and couldn’t find the stars I needed to in order to carry it out. Maybe the sky has changed enough for me to try drift aligning again (and I did get a tree taken down in my yard due to safety reasons). The other issue I’m having is some pretty nasty backlash depending on where my mount is pointing. It’s actually a common problem with my mount and one’s that’s easily remedied by taking apart the mount and following some not too difficult instructions – I just haven’t had the time yet to do so, but the next couple of days are going to be cloudy, so it’s on the agenda (hopefully tomorrow?).

4. I image from the roof over what was once a garage (but is now a combination kitchen/office). On top of this roof is a greenhouse in the front (one former owner was a locally famous botanist) and a shed in the back, where I keep my scope, mount, etc. There’s probably ten square feet behind the shed where I’ll set up my mount. Due to all the trees around here, I don’t think I’ll be able to get a pier until we can tear down the greenhouse and build a bedroom addition there (and an observatory on top). I’ll let you know when I win the lottery. I do definitely want to be able to go 20+ hours for an image – I’m usually limited to 3.5 hours a night depending on the target because of trees and everything – I’m even at the bottom of the hill. I love my house, but if I were an imager when I bought it 5 years ago, I might have chosen differently.
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Chris-PA 3.31
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Hi Lynn,

If I had Maxim DL already, then maybe I’d consider sticking with CS2 instead of moving to PixInsight, but the price of Maxim for stacking/combining is pretty close to the price of PixInsight, which can stack, combine and process - and apparently has some pretty neat tricks for processing that CS2 (or CS6) doesn’t have. I think if I move to monochrome, it would make more sense to get and learn PixInsight than Maxim DL, when I’ll probably end up moving to PixInsight eventually anyway.

I’d really like a nice small refractor as well. I love my Newtonian (despite its flaws), but I do travel quite a bit and have a comparatively portable mount. I’d love to be able to bring my rig to Germany with me - the skies where my wife’s from are waaaay darker than where we live. I probably wouldn't even be in this forum if I imaged from there.
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Chris-PA 3.31
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Bobzeq25:

I’ve been using the morning sky as my light source for flats. It sometimes works perfectly - there are some images I’ve been able to process without even using GradientXterminator. Other times, my flats fail completely but I don’t know what I’m doing wrong when it doesn’t work out. Spike-a-flat-looks nice, but I’m unlikely to spend that kind of money on a flatbox at this time. Maybe once my two toddlers are out of college? Like I said above, I'll probably try to make one on my own. I've seen people who use tablets, computer screens, the white t-shirt, as well as the sky - hard to pay $200+ when the sky is free, even if the results are more consistent. :/
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Chris-PA 3.31
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Peleks:
I actually have that filter and tried imaging with it once. My results were terrible! (I'm kind of embarrassed to bring you here, but: http://www.astrobin.com/253421/E/.) It gave everything a weird pink cast - I ended up throwing away all that data in my final image. Admittedly, a reflection nebula is not the best for a filter made for emission nebulae, so perhaps I should give it another try on something with a lot of Ha? Still, that’s currently the main strength with my camera/filter combination at the moment: It's awesome at capturing emission nebulae under light pollution. It's the galaxies and reflection nebulae that I'm having the most difficulty with.
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