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Introduction to Light Pollution Filters

Light pollution filters are any filters that can be used to combat the effects of light pollution. Light pollution often causes the image or view to have lower contrast, less detail, and usually adds undesirable colored gradients for astrophotography images. Image processing can help alleviate these issues, but a dedicated light pollution filter will be an even better solution and can produce beautiful images right from your own backyard.

Note for beginners to astrophotography: There are a lot of light pollution filters out there, so we recommend checking out this beginner-friendly blog post with visuals of how light pollution filters work and a list comparing which ones to buy.

Light pollution filters come in a variety of sizes and mounting options. Most astronomy camera users opt for either 1.25" or 2" mounted filters that can thread into a filter wheel or drop in to a filter drawer, though other unmounted options exist such as 31mm and 36mm filters. For DSLR/Mirrorless camera owners, most usually opt for a clip-in size filter for their camera type. When choosing a filter size, make sure you get one large enough to cover your entire camera sensor. For this reason, it's always recommended to get a size larger than you may need, in case you want to upgrade to a larger sensor camera in the future.

To understand how light pollution filters work, we first need to understand light bandpasses of filters. There are two main types of light pollution filters: multi-broadband and multi-narrowband. To learn more about each, continue reading on below. 

Multi-Broadband Filters

Optolong Filter Comparison

Best for imaging galaxies, reflection & dark nebulae, and star clusters

Multi-broadband light pollution filters are a great choice for photographing galaxies, reflection nebulae, dark nebulae, star clusters, and other broadband targets from under light pollution. Multi-broadband light pollution filters work by allowing large portions of the spectrum to pass through, but blocking out common sources of light pollution.

Though there's no true substitute for dark skies, broadband light pollution filters can drastically reduce the color gradients and glow effects often seen when imaging from light pollution. See the above comparison image from Optolong to see how a broadband light pollution filter can enhance the contrast and give more natural sky colors. While multi-broadband light pollution filters can be somewhat effective for imaging emission nebulae, multi-narrowband filters are much better suited for allowing light from emission nebulae to pass through.

Shop Multi-Broadband Filters

Multi-Narrowband Filters

Optolong Multi-Bandpass Filter Comparison

Best for imaging emission nebulae, planetary nebulae, and supernova remnants

Multi-narrowband filters, also known as multi-bandpass light pollution filters, are the ideal choice for any celestial object that emits light in a specific part of the spectrum. This includes emission nebulae, planetary nebulae, and supernova remnants, which all feature gases that emit light at narrowband emission lines. This includes Hydrogen Alpha (Ha, red color), by far the most common gas found in nebulae, and other prominent gases such as Oxygen III (OIII, aqua color), Sulfur II (SII, deep red color), and Hydrogen Beta (Hb, green color). Multi-narrowband filters allow multiple emission lines to pass through at once, meaning you can capture useful data on targets that emit multiple emission lines such as Hydrogen Alpha and Oxygen III in one go with a color camera.

Mutli-narrowband filters work by isolating these emission lines and blocking out everything else, effectively eliminating most light pollution. For this reason, multi-narrowband filters are best paired with astronomy-dedicated cameras or modified DSLRs, but they can have a limited response on stock DSLRs as well. Lower-end light pollution filters allow a wider bandpass, which lets in more light pollution than higher-end filters. Higher-end filters like the Radian Triad Ultra use a narrower bandpass, which allows the nebulae to appear more contrasted from the background of space. This leads to more pleasing images, and the ability to take great deep sky images even from heavily light-polluted areas.

Explore Multi-Narrowband Filters