Any tips for imaging under heavy light pollution?

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/

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?

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. :/

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 ;)

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.

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).

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

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.

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.

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.

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.

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. :/