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HOW LIGHT POLLUTION FILTERS WORK

Posted by Benjamin Newton on

Top 5 Reasons to Own A LP Filter

  1. Great for Astro and Milky Way Photography
  2. Reduces the orange/yellow haze from night sky caused by city lights
  3. Capture more accurate color at time of exposure
  4. Reduce editing time with a "cleaner" RAW File
  5. Filter also enhances sunsets and fall colors without effecting cool colors 

What's in a Name

Before we dig in we want to clarify the name of this filter as it is referenced many different ways depending on where you live

  1. Starscape - Available world wide
  2. Intensifier - Original Name. Changed to Starscape in 2020
  3. Light Pollution
  4. Red Intensifier
  5. RA54 Intensifier
  6. Didymium - Technical name for the type of glass being used

All of these names refer to one specific filter manufactured by Hoya filters. They are all the exact same filter providing the same results. Hoya uses a special glass called "didymium" glass that is created by blending and smelting specific types of glass and chemicals to create the filter properties. We do not use coatings applied to the glass like most manufactures. Our process provides more consistent and predictable results.

How It works

The filter targets specific wavelengths of light emitted by common Sodium and Mercury-vapor street lamps and blocks a portion of the orange/yellow glow as it passes through the filter. The effect can be dramatic or subtle depending on how strong the light source is and how much atmospheric haze is in the air.

As the light passes through the filter it selectively blocks specific areas of the light spectrum that most commonly cause that orange/yellow color spike. The light transmission chart below illustrates what parts of the color spectrum that are blocked by the filter and what colors pass through.

It is really important to note that this filter is not adding blue or changing the color of the scene. It is literally stopping specific areas of the color spectrum from passing through the filter. The camera never sees that light or color.

The end result is a "cleaner" RAW file without the orange/yellow glow polluting your image. And, it allows you to color correct and enhance colors without needing to compensate for the "pollution".

NOTE: The filter has a base filter factor (light loss) of 1/2 stop, but you may see a 1-2 stop difference in exposure depending on how much of your scene is lit by Sodium or Mercury Vapor lights.

I'll Just Fix it in Photoshop

You can to a point but it's not the same. Digital color correction normally works on 2 simple linear scales; Color Temperature and Tint. Color Temperature controls yellow to blue, and Tint controls magenta to green. If you adjust for the yellow/orange color in your image you will effectively add blue to the entire scene changing other colors in the scene as well. A skilled Lightroom or Photoshop user can use more advanced tools to essentially achieve what the filter will do at the time of capture, BUT that takes a lot more time and skill. 

Not Just for Light Pollution

The filter can also be used during the daylight hours to enhance red, orange and yellow colors. It was originally created for film photographers to "intensify" warm fall colors on overcast and cloudy days. The filter is still used today by digital and film photographers to target those specific colors for enhanced saturation while leaving the blue and green colors alone. Add a circular polarizer to this and you will have the ultimate filter combo to capture the best possible fall colors especially on those rainy, overcast fall days.

SOURCE: HOYA USA


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