Dealing with light pollution

Somewhere to ask questions about the best way to use SharpCap
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urbanite
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Joined: Sat Apr 28, 2018 4:32 am

Dealing with light pollution

Post by urbanite » Tue May 22, 2018 2:55 am

The usual apologies if this has been already covered. I am pretty new here and to EAA as well.

Like so many these days, I suffer the curse of light polluted skies--a red to white zone becoming ever whiter it seems. My setup is an AstroTech 72EDII with an ASI 224 camera, all riding a Celestron AVX GEM mount.

I seem to do fairly well with targets such as globular clusters. But am having difficulty capturing more nebulous things --the really good stuff--without washing out the background. Gradient removal in StarTools is somewhat effective. But I would like to capture the best image possible in live stacking as well.

Tweaking the histogram so that signal to skyglow seems optimal also frequently disables live stacking. I tend to have difficulty with live stacking generally. Maybe also due at least in part to light pollution?

I am in the process of fitting a focal reducer to my little refractor which should bring the focal ratio down to around f/4.8. I am hoping this might help.

Any advice would be appreciated.

galljj
Posts: 78
Joined: Wed Mar 01, 2017 10:14 pm

Re: Dealing with light pollution

Post by galljj » Thu May 24, 2018 3:19 pm

I think a light pollution filter is your first need. I use an Astronomik CLS ( the non ccd one).

Also, I'd suggest you go over to the cloudy nights EAA page https://www.cloudynights.com/forum/73-e ... equipment/ and search for unofficial sharpcap users guide. I assume you've already looked through the manual available on this site.

john

dts350z
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Joined: Fri May 18, 2018 6:00 am

Re: Dealing with light pollution

Post by dts350z » Thu May 24, 2018 8:55 pm

re your focal ratio, the light pollution will get brighter too, so focal ration won't help.

There is an argument to be made for aperture, although some disagree.

Yeah light pollution filter and an 10x the total integration time (compared to dark sky) is the answer, for LRGB or OSC.

Not sure why non CCD was recommended. In any case the white balance or channel weights will need to be adjusted.

NB shouldn't be nearly as much of an issue, but still plan on longer total integration (compared to NB under dark skies).

I just did an OSC galaxy from a white zone. 11 hours over three nights.

https://www.astrobin.com/346724/?nc=user
Last edited by dts350z on Fri May 25, 2018 3:24 am, edited 2 times in total.

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oopfan
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Location: New York
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Re: Dealing with light pollution

Post by oopfan » Thu May 24, 2018 10:53 pm

I know a guy who knows a guy who lives just a couple miles from center Detroit City. He's done some great work using narrowband SHO filters with a monochrome camera: Silicon II, Oxygen III, and Hydrogen-Alpha. Here is a photo that I took of M1 in Hydrogen-Alpha with the waxing gibbous Moon only 30 degrees away. I admit that I don't have problems with light pollution but I was impressed with what was possible in this case:

https://s3.amazonaws.com/oopfan-astroph ... rgan+B.jpg

Using all three SHO filters you can create a false-color image that can be quite beautiful. Me? I'm an old geezer -- monochrome is all right with me!

Brian

galljj
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Joined: Wed Mar 01, 2017 10:14 pm

Re: Dealing with light pollution

Post by galljj » Fri May 25, 2018 3:37 am

The CCD version cuts off the IR end of the spectrum at 700 nm, the non-CCD goes much farther. So you'll capture more energy, especially from galaxies.

If you are doing EEA type imaging, you'll not need much more than 20 minutes integration to get acceptable images. See https://www.cloudynights.com/gallery/album/9173-asi294/, all taken from a red zone. Not like traditional AP, but good enough for me.

Above all, enjoy !

j

urbanite
Posts: 5
Joined: Sat Apr 28, 2018 4:32 am

Re: Dealing with light pollution

Post by urbanite » Mon May 28, 2018 4:26 am

I have tried imaging with one of the cheaper LP filters, and without. Don't have enough overall experience yet to decide which works best. I am wondering how important dynamic range of the camera might be in beating light pollution. Narrowband certainly sounds like a viable option if longer integration times are possible.

Thanks all for advice and there are some really fine images here. Gives me hope!

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