PureNight FAQ

Lonely Speck PureNight Light Pollution Reduction Filter

PureNight Frequently Asked Questions

Below are the most frequently asked questions for the PureNight Light Pollution Reduction Filter by Lonely Speck. If you have a question not covered here, please ask in the comments section at the bottom of this page or contact us directly.

How do I care for my PureNight filter?

PureNight should only be cleaned with a clean microfiber cloth and a lens cleaning solution safe for coated optical glass. We recommend Zeiss Lens Cleaner.

Please note: We do NOT recommend use of lens cleaning solution on the SharpStar, as it will damage it.

Where can I order?

The PureNight light pollution filter is sold exclusively on lonelyspeck.com by Ian Norman and Diana Southern, creators and owners of the Lonely Speck blog and the PureNight filter. Any other website or store selling a light pollution filter under the PureNight or any other name is not an authorized seller of Lonely Speck’s light pollution filter, and the product being sold is not manufactured or sold by Lonely Speck or covered by the Lonely Speck 100% satisfaction guarantee. For any questions about unauthorized sales of the PureNight filter, please email [email protected].

The PureNight filter can be purchased only through the Lonely Speck website.

How can PureNight improve my night photography?

PureNight will improve the colors and contrast of an image taken in any location impacted by light pollution.

You cannot achieve the same level of improvements with post-processing.

Why is light pollution a problem and how does PureNight help?

Light pollution is a problem that astrophotographers face across the world. Sodium vapor lamps are very commonly used in industrial and street lighting, and light pollution from these lamps can be visible in photos from a hundred miles away.

Even dark sky destinations are impacted by light pollution, as shown in the photo below of Tekapo, New Zealand.

The PureNight is made of didymium glass, which filters out sodium light to give the photographer an image vastly less impacted by any surrounding light pollution.

lonely-speck-pure-night-light-pollution-filter-example-no-filter-2020 lonely-speck-pure-night-light-pollution-filter-example-with-filter-2020

In what situations will PureNight make a difference?

The PureNight will make a noticeable improvement in the quality of your night sky images in any location with a city, town, or other source of light pollution influencing your image.

In today’s world, places without any influence of light pollution are few and far between.  In the U.S. light pollution affects even the darkest skies, including national parks located many miles from the nearest artificial light source. Even under the extremely dark skies of Death Valley, California, light pollution is still present and will impact your photography.

In downtown city skies, the PureNight won’t magically reveal the Milky Way, but it will filter out the ugly orange tinge of sodium lamps for more natural looking urban nightscapes.

How does the PureNight filter work?

PureNight blocks the transmission of yellow-orange light between about 575nm and 600nm wavelengths, the same wavelength as sodium vapor lamps.

In the example above with the PureNight installed, notice the drastic intensity change in the yellow-orange lights of the town, resulting in a more pleasant night sky image.

Below is a transmission curve of the PureNight.


What kind of improvements can I expect from the PureNight?

The benefits of PureNight extend beyond the noticeable improvement in the colors of the image.

The biggest advantage of the PureNight is an increase in contrast in light polluted areas. Light pollution reduces contrast by illuminating moisture and particles in the air. Filtering out this light makes the surrounding sky darker. An example of this improvement can be made by making a comparison between a filtered and non-filtered image and adjusting them in post processing to match in both white balance and exposure.

lonely-speck-pure-night-light-pollution-reduction-filter-los-angeles-suburb-no-filter lonely-speck-pure-night-light-pollution-reduction-filter-los-angeles-suburb-with-filter

The difference is subtle but most noticeable around the galactic center. If we take a closer, 100% magnified look at the galactic center, we can see that the image made with the PureNight retains more of the subtle reds and pinks of the nebulae and shows higher contrast around the galactic center:

pure-night-white-balanced-no-filter pure-night-white-balanced-after

The PureNight has a filter factor of about 1.5, meaning that there will be a reduction in light transmission of the image by about -0.6EV, depending on the amount of light pollution in the scene. To get a better idea of what to expect, feel free to download our sample photos in RAW DNG here. (95.6MB, .zip)

How does PureNight differ from a Red Intensifier like the Hoya Intensifier?

We love the Hoya Red Intensifier. It’s certainly an affordable didymium filter option that we recommend. Limited availability of the Hoya Intensifier and the lack of a square version led us to pursue the design of the PureNight. We use an improved filtration glass with stronger filtration properties than the Hoya Intensifier.

PureNight is available for square filter systems (85mm, 100mm and 150mm sizes). This allows photographers to use a single filter system across their lens collection.

The final improvement: the Hoya Intensifier is made of uncoated or single coated glass which is drastically worse in flare-inducing conditions (e.g. if there is a bright light source against a dark background).  To improve upon this shortcoming, PureNight is multi-coated for highly anti-reflective properties that greatly improve contrast and reduce flare.

Which filter holder do you recommend?

To mount a PureNight you will need:

  • an appropriately sized square filter holder system
  • a system-compatible adapter ring, sized for your lens filter thread diameter


To determine which size filter holder system (85mm,  100mm, or 150mm) and which adapter ring you will need, you will need to know your lens’s filter thread diameter. The filter thread diameter is usually marked in millimeters on the front of your lens with a diameter (⌀) symbol like this:


In this example, the lens shown has a filter diameter of 49mm. Depending on your lens’s filter diameter size, we recommend the following systems. (In general, pick the system size that’s larger than the thread diameter of your lens).

If you don’t already have a filter system, here are some recommendations:

85mm (lenses up to filter diameter of 77mm):

Formatt Hitech 85mm Aluminum Holder (Amazon / B&H) and Formatt Hitech Adapter Rings for 85mm Aluminum Holder (Amazon / B&H)

100mm (lenses up to filter diameter of 105mm):

Formatt Hitech 100mm Aluminum Modular Holder (Amazon / B&H) and Formatt Hitech Adapter Rings for 100mm Holder (Amazon / B&H)

150mm  (certain wide angle lenses with fixed hoods):

Haida 150mm Filter Holder (Amazon / B&H)
Lee SW150 Filter Holder (Amazon / B&H)
NiSi 150mm Filter Holder (Amazon / B&H)

Do you ship outside the USA?

Yes, we ship internationally.

Shipping fees vary by country.

Our international orders are shipped via USPS first-class mail and usually take at least 7-14 business days to arrive. Tracking may or may not be available depending on the international destination. As the buyer, you are responsible for any import taxes (VAT, etc.), duties and custom fees that your country may impose at the time of receipt of the shipment.

All international shipments are marked on the customs form as “Merchandise” with an accurate description of the value and contents (“Photographic Filter”) and labeled with the proper six digit HS Tariff Code for photographic filters: 900220. Please check with your local postal service for status updates on your order once it has left the USA.

What if my question isn’t answered here?

For further questions, just ask in the comments below or contact us directly.

54 Replies to “PureNight FAQ”

  1. Mr. Norman,
    May I ask what is your definition of “very short focal length” please ?
    I’ve viewed responses from other light pollution filter manufacturers that caution to use an 80mm minimum to avoid the vignetting.
    Thank you.

    1. Hi Belinda,
      PureNight works via transmission cut filtering rather than with the use of interference filtering as other light pollution filters. This means PureNight is compatible with all focal length lenses, including extremely short, wide angle lenses such as an 8mm, 10mm, 14mm, etc. fisheye or wide angle lenses. Even with short lenses like these, the PureNight operates without vignetting problems.

  2. Your filter is made of didymium glass, which is homogeneous and not interference based. I understand it will filter light the same no matter whether it comes straight into the lens or on extreme side angles such as with an ultra wide angle lens. Are all the other (competing) filters interference based, which would have severe trouble working as intended with extreme side angle light into ultra wide lenses which lengthens the interference spacing and change the filtered frequencies? And wouldn’t having extreme side angle light into an interference filter cause it to be smeared linearly across the sensor from the light bouncing back and forth different number of times (1 or 2 or 3… etc) before entering the camera? If so, that problem would be eliminated with your homogeneous filter with non-reflective coatings, correct?

    1. John, yes, one of the large advantages of using the PureNight over similar light pollution reducing filters is that it does not have any issues when used with very short focal length lenses. Many light pollution filters rely on special coatings that target specific wavelengths but these coatings do not work at high incidence angles and cause heavy vignetting or color cast when used on even moderately wide angle lenses. The PureNight does not have this problem and works wonderfully on ultra-wides.

  3. Hi Ian, I have one of the light pollution filters, I’m from New Zealand so our light pollution is somewhat limited from the US, can you recommend a white balance to use please? I have noticed that on your examples it is set at daylight is that a recommended practice with the pure night filter?

    1. Hi Leanne, yes, I recommend daylight white balance. That should still result in a balanced looking image. Any small corrections can be made in post processing afterwards.

  4. Still waiting for PureNight to be restocked… 🙂 Any idea about the schedule, please? (although I have subscribed for the stock alert)

  5. Looks like I missed the window to order the 85 mm version. Do you have a timeline for when more will be available?

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