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Tips to image in city skies


Nova2000
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Hi

I wanted to know some techniques to image in a city. 

1-should I build a observatory (polestar sometimes not visible) 

2-lp filter_does this filter affect image quality? 

3-h alpha and other Narrowband-filters_ive heard that these filters block other light wavelengths. 

4-bigger apperture or smaller? 

need help please. 

Thankyou 

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0. A car big enough for your equipment, so you can drive to a location with dark skies ( :wink: :wink: )

1. An observatory is always good, since it will block lights shining directly at you, destroying any chance for night vision.

2. Lp filter is only good it seems, in moderate light pollution. The effect of a LP filter will also depend on the type of light pollution. Most filters are designed to block sodium and mercury lights, not LED lights.

3. Narrow band is the way to go if you have more light pollution. The narrow transmission band will block most unwanted light. The narrower the better. But good filters will cost you almost as much as nr 0.

Cheers,

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The only way a city imager can match dark site results is in narrowband, the tighter the bandpass the better. You can do broadband colour imaging from the city and people do wonders, but if you want straightforward, top class results from heavy LP use a mono camera and an Astrodon 3nm Ha filter.

Olly

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8 hours ago, Nova2000 said:

Hi

I wanted to know some techniques to image in a city. 

1-should I build a observatory (polestar sometimes not visible) 

2-lp filter_does this filter affect image quality? 

3-h alpha and other Narrowband-filters_ive heard that these filters block other light wavelengths. 

4-bigger apperture or smaller? 

need help please. 

Thankyou 

An observatory helps because you can leave your gear setup ready for instant use - security issues aside of course.

LP filters affect colour mostly, they will introduce a bias (usually towards Green or Blue). They don't help much for serious pollution - they are not a magic wand.

H-alpha is the best option under light pollution, they let through only the light with a narrow bandwidth according to the type (selected wavelength) of the filter.

Bigger aperture usually adds longer focal length which makes life difficult in other ways - more difficult to track accurately, heavier, and narrower field of view. Use large aperture and long focal length for small targets (galaxies, planetary nebula etc..). Use moderate size scope (80-130mm and less than 1000mm focal length) for a wider range of objects.

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4 hours ago, Nova2000 said:

What exactly is the advantage of a roll of observatory vs the dome (ready made) observatory? 

A roll off roof is much easier to build than a dome, and it has the advantage of not looking like a dome observatory to the casual observer. Anyone looking at it in daytime when the roof is closed will think it's just a garden shed. Where I live is a low crime area, but it still pays to not advertise that I have something worth stealing.

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Another advantage of the ROR is that you don't have any dome obstructions,  I live in SE London and image, I find the brighter objects OK, and even with NB I find only the brighter targets work on Oiii and Sii.  I also made the mistake of buying a POD observatory which obstructs the Zenith, so I then had to build a POD Zenith table so I could slide the roof off, but it's a real palaver and still obstructs on one side, so I made that side the side where the house is.  

Carole 

 

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20 hours ago, Nova2000 said:

You mean to say a mono dslr? 

I can see till mag 3.5 here I don't what kind of sky this is called as. 

The car idea was nice actually, like NASAs air observatory. ?

Mono ccd or cmos, not dslr. But go for a cooled camera.

Mag 3.5 is almost like twilight here. That's serious lightpollution. you should definitely check out narrowband imaging.

NASA has the scope mounted inside the plane. Unless you have Nasa-like funds, you shouldn't try imaging from a car/truck. Just use it for transportation.

:icon_biggrin:

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