Light Pollution and Low Light Photography

Overview

Light pollution is one of the biggest drawbacks of taking Star-Trail photographs. Light pollution is one of the biggest drawbacks of taking low light photography. Light pollution comes from cities, street lamps, moon and sun. There are other sources of light pollution as well, but I will be focusing on the primary sources in this article.
 

Types of Light Pollution

Light pollution is one of the biggest drawbacks of taking Star-Trail photographs. Light pollution comes from cities (Street Lamps) lights which are on at night, the moon (especially full moon) the sun (glow of the sun after sunset on the horizon). Thus to counter light pollution you have to seek the darkest skies, when there is a new moon (or 60 minutes after moonset), away from the city, be 90 minutes after sunset and a few clouds (clouds can reflect sunlight as well, and Winter is usually best for this kind of photography due to there not being a lot of clouds).

Light Pollution Source
Description
Image
SUN
The sun is obviously one of the biggest sources of light-pollution in your photographs. Even after the sun is setting can the glow of the sun affect your photograph, even after sunset.
TIP: Star shooting at least 90 minutes after sunset
Moon
The moon causes a massive amount of glow in the sky, especially when it is full moon, and will definitely block most of your visible stars in your photographs.
TIP 1: Photograph on a new moon
TIP 2: Photograph 60 minutes after moonset
 
 
Street Lights
Street lights or any sharp lights can interfere greatly with your photograph, and reduce the amount of stars you can see. But you can incorporate it into your photograph as part of the composition, or use the appropriate settings to minimize the effect of the glow from street lights.
 
TIP 1: Be as far away as possible from Street Lights
TIP 2: If not possible use the correct settings for Time-Lapse Star trails and make it a feature of your photograph.
City Glow
Glow from a city will as well reduce the amount of stars you can see.
TIP: Seek the darkest skies for taking Astro-photos

 

How to Compensate for Light Pollution

Increase your aperture

The mid-range f-stops are ideal for shooting photos at night in light polluted skies. The lower numbered f-stops produces too much light, the upper numbered f-stops produced too little light and too little star details. Use ISO 6400 (drawback is too much noise in photograph) and tungsten white balance for all the photos. The ideal range thus for colours in relation to star details were between f/8 and f/13 as seen in the next composition.

Exposure to the Right (ETTR)

Overview

Exposure to the right (ETTR) is a method whereby you overexpose your photograph in light polluted skies and then modify the exposure in a software program to reduce the over exposure to normal levels. By using the correct settings you will be able to capture more star details in your photographs.

How to do it

Make sure you photograph in RAW mode for this method. Set your Camera’s EV to +2 (2 stops brighter), ISO to 1600 and shutter speed to 30 seconds. This will cause the photo to be overexposed. Open the photograph in Light Room and start modifying the exposure to be more darker (back to normal EV 0 level), can modify the contrast as well to try and remove the overexposed bits in your photograph.

I personally do not use this method: as I like to use the photographs as natural as possible with as little editing as possible, but you are welcome to try it. 

Conclusion

Do not be perturbed if you cannot take stunning photographs in Light polluted skies. As indicated in this article: there are many ways in which you can overcome light pollution by using the correct settings with regards to ISO, Aperture and ETTR methodology.

Happy Shooting!
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