Hello Astrophotographers:

I have seen some wonderful pictures on this website, presumably taken from good locations with small to moderate size telescopes. My "observatory" is in my light polluted back yard in a suburb of Los Angeles, where the visual limit is +3.5 on a good day for about 50% of the sky. It consists of three permanent stepping stones in the grass, which support the legs of a movable, but heavy GM100 tracking tripod. Should I go to a good site by taking the tripod plus all the gear and drive two hours plus into the desert? The first question is: How well can I do from my backyard. The second question is: What did I loose? You can help me with the second question.

To answer the first question I took pictures of Alcor and Mizar in the Big Dipper with my Nikon D40 at iso400 and a 85mm f/1.8 lens stopped down to f/2.8. At f/2.8 this lens produces a sharp 10 degree diameter field of view. The center 1x1 degree of the image resulting from coadding 10 exposures at 30 seconds each is shown below zoomed into the orginal 19 arcsec/pixel at 200%.The individual exposures were limited to iso400 and 30 seconds because the background level reached 50% of full scale. The star chart shows stars to +12.5, matching the faintest stars in the picture. Caesar's double is actually a triple (+2.2, +4.0 and +7.9), and the +7.9 two +12 companions.

Maybe you can help me with the second question if you regularly shoot at a good site and if you have similar equipment to mine: Take a 30 seconds picture of Alkor and Mizar and post it here with the details of where and with what equipment the shot was taken. Maybe we all will learn something.

Thanks in advance.

hha

Attached Images

Alcor.Mizar.10x60sec.85mm.f1.8@f2.8+StarChart+12.5.jpg (143.3 KB, 63 views)

I also live in a light polluted area. Not bad at night though. The giant Oaks that I always loved so much have become a challenge. I'm just getting going into astrophotography, but feel things will work out. May be much different for deep sky objects.

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Bill
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Celestron C130
Orion 100MM F6
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Celestron Astro Binos

Planetary, major star clusters and double star imaging are not a great challenge at all from light polluted skies. It's really a non issue unless you are trying to image a very faint Palomar globular or something like that. Its when you go to image nebula and galaxies that light pollution becomes an issue. Parts of these are magnitude 24 per second of arc. That's faint and that's where you get killed by light pollution.

There are two solutions. One is to do narrow band imaging. This isn't bothered by light pollution much as you are looking at such a narrow part of the spectrum.

But that doesn't work for galaxies and reflection nebula. Here the second ploy comes into play. One heck of a lot of exposure time. Since there's a lot of light coming in the sub exposures will have to be short. 5 minutes is likely the maximum. I know one imager who images from downtown Berlin! I might use 4 10 minute images for say M88, he would use 70 5 minute ones. But with that much data you can deal with the light pollution quite well. He can't go as deep as I can living in the middle of a forest miles from anything but he can do very well indeed. Color gets a bit tricky with all the light sources putting colored gradients in the image but he seems to handle that well too. I have trouble with the moon. So some processing skill is needed. The point is it can be done even from downtown Berlin.

His web page is private so I can't link an image.

But here's the web page of an imager that images from the middle of Silicon Valley. That has skies at least as poor as yours. He's contributed several images to the Image of the Day website taken from his severely light polluted skies. While he does mostly narrowband imaging as the URL indicates he does luminosity and LRGB imaging as well.
http://www.narrowbandimaging.com/

Rick

Rick:

Thanks for the response.

[QUOTE=RickJ;1199965]Planetary, major star clusters and double star imaging are not a great challenge at all from light polluted skies.

I was tryning to be more quantitative. There is little doubt that one can get around some light pollution limitations by using narrow band imaging or brute force integration time. In comparing results with comparable aperture and focal length (within factor two) on the same object (like Caesar's double or M42) and comparable exposure time (within factor of two) from good sites and light polluted sites, we learn the price payed for the convenience of a suburban backyard observatory. Is it a factor of two in integration time or a factor of 100? As you indicated, some things may not be possible at all.

Your location "deep in the woods" may make an interesting comparison point.

hha

As I mentioned, double stars are worthless for any such test as they are hardly bothered by light pollution. Even M42 is bright enough that it isn't much of an issue. I've seen shots of it from the DC area in 20 minutes with a 4" scope and DSLR that rival what I could achieve in the same time from my skies. Maybe a bit more noise in the DSLR image but it isn't cooled so how much of that is due to light pollution and how much to temperature? I have no idea.

The penalty is very object dependent. The fainter it is the more additional time you need. This is why double stars aren't bothered. Most are far brighter than nebula on a square second of arc basis being near point sources.

For a typical faint fuzzy galaxy my friend in Berlin needs 3 to 9 times the exposure time I do but he's using a different camera on a different scope at a different f ratio at a different temperature and and has different processing skills than I do. How that would translate to you I can't fathom or how it would work if he and I traded places. There are just too many other variables in the mix.

Rick

hha,

I believe you can do quite well from your backyard. My observatory in about three miles north of the runways at LAX. The light pollution map is attached, with the cross right smack in the middle of the 8-9 on the Bortle scale with the comment "Most people don't look up."

Nonetheless, I have been able to get decent astophotos. As Rick pointed out, planetary or Moon imaging is pretty simple anywhere, as the objects are so bright. But I'm able to do deep sky imaging as well. My set-up for deep sky is a C-11 or NP-101 on a CGE mount with a ST-10XME camera. I use a Hutech light pollution filter that has helped reduce the color balance problems I have had (primarly too much green from the sodium vapor lights).

Rick is correct about the approach. Take lots of data (lots and lots of data!) and use the best processing tools you can find. I use MaximDL for image capture and dark/flat/bias calibration, CCDStack for alignment and stacking, PixInsight for image enhancement, and Photoshop for finishing. PixInsight has great background gradient removal tools that really help in creating an even image with the light pollution reduced. Russ Croman's Gradient Xterminator absolutely performs miracles.

Narrowband is also a good way to go. No worries about light pollution or the Moon.

Here are some of my images, all taken from West LA:

• NGC 891 -- Spiral Galaxy in Andromeda
• M63 -- Spiral Galaxy in Canes Venatici (poor seeing on this one)
• Horsehead and Flame Nebulas HaRGB
• The Bubble Nebula HaRGB
• The Double Cluster in Perseus

I admit that these certainly aren't APOD-quality images, but I am still learning. But I do think they show that you can get decent images from a very light polluted location. The convenience of having a set-up at home means that I do more imaging than I would if I had to pack everything up for a 2-hour drive to the desert.

Clear skies,

--Andy

Attached Images

MrVstCAlp.gif (11.1 KB, 4 views)

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Observatorio de la Ballona

Andy:

No doubt one can work around some of the light pollution problem, and you are. However, if a picture of the double cluster to a depth equivalent to your picture, for which you took 5 pictures at 2 minutes each with a 101 mm aperture scope ( 600 seconds total) could be taken with a 100 second total exposure with the same scope in a dark sky, then working in your backyard becomes much more attractive. On the other hand, if it takes 1 second instead of your 600 seconds, many object would be totally out of reach, and the 2 hour drive into the desert might have to be reconsidered. Somebody must have already done some tests to evaluate this ratio.

Very nice work on your website, without even considering your location.

hha

I've already covered this, go back and look at my posts, pay attention to the part about stars vs faint fuzzies. Planets and clusters are hardly bothered by the pollution as far as exposure time goes. Gradients add to the processing time but the final result will be very similar.

Rick

hha,

Hard to evaluate on stars. They are generally bright enough so that the real problem is gradient removal and color correction.

The difference comes on very faint objects. I tried very hard to get NGC 2403 imaged, and shot a lot over several nights. But in the end, the fact that it is a very dispersed object made it just too difficult to get the faint areas of the galaxy. They weren't sufficiently brighter than the sky glow. In fact, on many DSOs, the sky glow is only a couple of hundred ADU less than the object itself.

And that's why we bought a house out in the Anza area. Relatively close (120 miles) and relatively dark. And acceptable to the boss.

Thank you! I appreciate the complement and thanks for looking.

Clear skies,

--Andy

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Observatorio de la Ballona

Andy:

I found this website (by the author of the IRIS software) which discusses results obtained with a Canon 350D of faint nebulosities taken under "suburban conditions"

http://astrosurf.com/buil/gallery/fsq106/ds1.htm

Very encouraging results.

I have been at the OCA Anza observing site many times. The sky is getting worse there due to the lights from the Casino.

hha



[QUOTE=andyschlei;1200538]hha,



Hard to evaluate on stars. They are generally bright enough so that the real problem is gradient removal and color correction.

The difference comes on very faint objects.

hha,

That is great stuff! And very encouraging for your equipment set-up. That is really excellent work.

I've been by the site a couple of times. It is about 7 miles east of where I'm at. The casino isn't bothering me much.

From my location, the big light sources are Palm Springs, Temecula, and Escondido/San Diego. The sky to the southeast is very dark. It's no New Mexico Skies, but it's close to home and much darker than West LA. And it's quiet and very pretty IMHO.

Clear skies,

--Andy

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Observatorio de la Ballona