Light pollution sucks. Thanks to the electric light, humankind's view of the cosmos is in a steady decline. Dark skies are a thing of the past for most of us. Is there a way to combat this? Many filter manufacturers offer lens filters that claim to reduce light pollution in your photographs. Not only are they all unique in their specifications, they range in price from reasonable to costing more than the lens on which you are mounting the filter.
Photographs © Todd Vorenkamp
Light-Pollution Sources
Light pollution comes from any artificial light, be it on a suburban porch or a city street lamp. If you think your town has a lot of street lights, New York City operates more than 250,000 of the dark-sky fighters—many unshielded. At 305 square miles, that is more than 820 street lamps per square mile. No wonder it is "The City that Never Sleeps."
The traditional orange-hue, low-pressure sodium-vapor street lamp emits light very close to 589nm on the visible spectrum, with a color temperature around 2700K—like household incandescent bulbs. Some lamps use mercury-vapor bulbs that have wavelengths between 400-600nm and a color temperature around 6800K. Many sodium and mercury-vapor lamps are being replaced with energy-efficient LED lights that transmit at a huge range of wavelengths (in outdoor lighting, it is usually a shorter wavelength) and have a color temperature that varies from 2200K-6000K. While good for your local municipalities' electrical bill, LED lights increase light pollution due to their increased brightness over traditional lamps, and their whiter light has potential health ramifications.
Around the house, we create our own light pollution. When photographing in my backyard, not only do I have to contend with the street lamps nearby and the hospital around the corner, but I know that my kitchen lights will wash out the night sky if I fail to turn them off before heading outside.
The Filters
I searched the B&H Photo website for "light-pollution filters" and came up with this list of suspects for my test. In the world of astrophotography and astronomy, there are many different types of light-pollution filters, not only for optics, but there are sophisticated astrophotography light-pollution filters that mount directly in front of the sensor of a digital camera body. For this test, I narrowed my search to lens filters that came in the 77mm thread size and advertised "light pollution" in their product descriptions and selling points. When compared to filters that get inserted in camera bodies or telescope eyepieces, the filters tested here are more for "casual" night photography, because they screw onto the front of the lens like any other filter. Basically, the filter's job is to reflect (or absorb) the wavelengths of light that are generated by artificial city lighting, while letting the rest of the visible spectrum through to your lens and sensor. If you want to dig deeper and get into the science of all of this, you can certainly find more on the Web and in books. But, in the meantime, let's press on and see some test results.
The filters are listed here with pertinent information from the product descriptions.
•No filter – Test control
•Heliopan 77mm UV Filter – Test semi-control using a standard ultraviolet (UV) protection filter. Absorbs ultraviolet light.
•Ice 77mm Lipo Light Pollution Filter – Absorbs yellow sodium-vapor light. 1.25x filter factor.
•Tiffen 77mm T1/2 IR Filter – Blocks Near infrared (IR) to IR 680-800nm. 1.41x filter factor.
•SLR Magic 77mm Image Enhancer Filter – Prevents infrared light pollution. 1x filter factor.
•B+W 77mm UV/IR Cut MRC 486M Filter – Blocks 88% of UV light at 380nm, 95% of IR light at 700nm. 1x filter factor.
•Haida 77mm NanoPro MC Clear-Night Filter – Absorbs yellow sodium-vapor light. 1.25x filter factor.
•NiSi 77mm Natural Light Filter – Blocks yellow sodium and mercury-vapor light, as well as yellow light from low CRI LEDs. 1.5-2.8x filter factor.
•Schneider 77mm True-Cut 750 IR Filter – Blocks 50% of light at 750nm and progressively eliminates IR after 750nm, preventing infrared light pollution. Schneider offers another version that is targeted at the 680nm range. 1x filter factor.
•Kenko Astro LPR Type II Filter – Engineered to block the light emitted from the most common types of street lights, especially gas-charging mercury lamps and gas-charging sodium lamps. Recommended for 100mm telephotos or greater.
The Tests
I wanted to try this gaggle of light-pollution filters to see if some worked better than others, and if my dreams of a magical light-pollution eraser would come true. Could I photograph the Milky Way from a city rooftop?
To mix the tests up a bit and experience different levels of light pollution, three locations were chosen.
- A rooftop, in Downtown Brooklyn, NY. New York City may be the light-pollution capital of the world.
- A backyard in a small town of more than 20,000 people, about 140 miles outside of New York, with a downtown area, about ¼ mile from a well-lit hospital with neighborhood street lamps.
- A park 10 miles outside of said small town, in a smaller town of 8,000.
For the trials, I wanted to do a mix of wide-angle, normal, and telephoto sky shots. I also intentionally pointed my camera in the direction of well-lit buildings and other sources of light pollution—compositions I would never attempt if trying to do an astrophotograph for printing!
All images were captured on a Fujifilm X-T2 mirrorless APS-C digital camera, using the following lenses: Samyang 12mm f/2.0 NCS CS, Fujifilm XF 23mm f/1.4 R, Fujifilm XF 35mm f/1.4 R, Fujifilm XF 90mm f/2 R LM WR, and Nikon AF DC-NIKKOR 105mm f/2D. To minimize star motion when shooting outside the city, the camera and lenses were mounted on an iOptron SkyGuider Pro EQ Camera Mount.
Here is a list of the test subjects:
- City – 12mm – Starscape including a waning gibbous moon, Jupiter, and surrounding buildings. 18mm equivalent.
- City – 23mm – Buildings with Venus and the stars Castor and Pollux of the constellation Gemini. 35mm equivalent.
- City – 35mm – Buildings and Venus. 50mm equivalent.
- City – 90mm – Jupiter and surrounding stars. 135mm equivalent.
- City – 90mm – Milky Way section, including Saturn and the Lagoon Nebula, with a crazy bright building in the frame.
- Town – 12mm – Backyard photo with the house, pool (with solar-powered LED-illuminated chlorine dispenser), neighbor's house, and the hospital in the frame. Thin clouds make an appearance, as well.
- Town – 12mm – Starscape featuring part of the Milky Way (not the galactic center) with the camera facing in the direction of the downtown area.
- Town – 23mm – Starscape, same night and camera position as the previous test, but a tighter crop on the skies.
-
Park – 12mm – Wide-angle Milky Way shot featuring a building and landscape in the foreground.
- Park – 23mm – Milky Way detail, including Saturn and the Lagoon Nebula.
- Park – 35mm – Milky Way detail, with a tighter crop on Saturn and the Lagoon Nebula.
- Park – 105mm – Milky Way detail featuring Saturn and the Lagoon Nebula. 158mm equivalent.
None of these locations would ever qualify as "dark sky" areas, and all of them experience light pollution at different levels.
All the images were shot as raw files with the white balance (WB) set to Auto. Here is how I processed the various image series.
Originals: These images are almost straight out of the camera (SOOC), but on a few I tweaked the exposure on the no-filter shot, and then adjusted exposure to match on the images where there was an EV-changing filter factor. The UV, SLR Magic, B+W, and Schneider filters had a filter factor of 0. The Ice, Tiffen, Haida, NiSi, and Kenko filters darken the exposures a bit.
WB Fluorescent: These images are identical to the original shots, but the WB was changed to the fluorescent setting in Lightroom.
WB Neutralized: On some of the urban images, I neutralized the WB for each image in the same area of each frame.
Adjusted: Using the no filter image, I adjusted the WB and "Presence" settings in Lightroom, as well as adding some noise reduction. I then applied the same adjustments globally across the filtered images… for better or worse.
Here are the City Landscapes (Tests 1-5):
TEST 1A: Starscape including a waning gibbous moon, Jupiter, and surrounding buildings. 18mm equivalent.
TEST 1B: Same images as Test 1A, but with WB set to fluorescent in post-processing.
TEST 1C: Same images as Test 1A, but with WB neutralized in post-processing using the eyedropper tool at the same area in each image.
TEST 2A: Downtown Brooklyn buildings, with Venus and the stars Castor and Pollux of the constellation Gemini. 35mm equivalent.
TEST 2B: Same images as Test 2A. WB set to fluorescent.
TEST 2C: Same images as Test 2A. WB neutralized in post-processing using the eyedropper tool at the same point in each image.
TEST 3A: Downtown Brooklyn buildings, with Venus "setting" toward a skyscraper. 50mm equivalent.
TEST 3B: Same images as Test 3A. WB fluorescent.
TEST 3C: Same Images as Test 3A WB Neutralized.
TEST 4A: City rooftop view of Jupiter and surrounding stars. 135mm equivalent.
TEST 4B: Same as Test 4A, with WB set to fluorescent.
TEST 4C: Same images as Test 4A, with post-processing adjustments in Lightroom applied equally to all images.
TEST 5A: A section of the Milky Way, including Saturn and the Lagoon Nebula, photographed from the Brooklyn rooftop with a bright building in the frame.
TEST 5B: Same as Test 5A, with WB to fluorescent.
TEST 5C: Same images as Test 5A, with post-processing adjustments in Lightroom applied equally to all images.
Please click here to view Town Photos (Tests 6-8); click here to view Park Photos (Tests 9-12) along with my conclusions.
