Using Light Pollution And Lrgb Filters Together: A Guide

Light pollution filters are a great way to improve your astrophotography, especially if you're shooting in light-polluted skies with a DSLR. These filters can help you capture impressive images of deep-sky objects from the city, but not all filters are created equal. The best filter for you will depend on your unique imaging location and the types of projects you like to shoot. For example, broadband filters are ideal for capturing more natural-looking images of galaxies, reflection nebulae, and dark nebulae, while narrowband filters are best suited for emission nebulae and supernova remnants. Additionally, the type of camera you use will also determine the right light pollution filter for you.

When choosing a light pollution filter, it's important to consider the size of your camera sensor and the specific wavelengths of light you want to block or allow through. Modified DSLRs, for instance, require larger filters to avoid vignetting issues. It's also worth noting that narrowband filters with smaller bandwidths typically offer better transmissibility, resulting in sharper images.

Some popular light pollution filters on the market include the Optolong L-eXtreme, SVBONY SV220, and Optolong L-Quad eNhance. These filters can help you capture stunning images of objects like the Flaming Star Nebula and the Veil Nebula, even in light-polluted environments.

In conclusion, light pollution filters are a valuable tool for astrophotographers, especially those shooting in urban or suburban areas. By selecting the right filter for your camera and imaging goals, you can significantly enhance your images and capture the beauty of the night sky.

Light pollution filters for colour cameras

Light pollution filters are designed to suppress the emissions generated by artificial lighting, such as street lamps, and are particularly useful for astrophotography in urban areas. They can improve the clarity, colour and contrast of images, but they are not a substitute for dark skies.

Light pollution filters are available for both colour and monochrome cameras. For colour cameras, there are two main types: broadband filters and multi-narrowband filters. Broadband filters capture more natural-looking images, while multi-narrowband filters aggressively block most wavelengths of light in the visible spectrum, allowing only narrow bandpasses of light in key areas to pass through.

Broadband filters are ideal for capturing galaxies, reflection nebulae, dark nebulae and natural star colours. They are also a good choice for landscape astrophotography. However, they let a little artificial light through, so they are less effective in areas with high levels of light pollution.

Multi-narrowband filters, on the other hand, are best suited for emission nebulae and supernova remnants. They can be used to capture impressive deep-sky images, especially objects with a strong signal in the hydrogen-alpha wavelength of the spectrum. However, they may result in images with an overly red cast, which can be corrected during the image processing stage.

When choosing a light pollution filter, it is important to consider the type of camera and the specific light pollution issues in your area. For example, if you live in an area with yellow sodium vapour lights, you will need a filter that blocks this type of light. It is also important to select the correct size filter for your camera body and lens.

Some popular light pollution filters for colour cameras include:

• Optolong L-eXtreme: a dual-band filter that isolates wavelengths of light emitted by many deep-sky objects, resulting in images with better contrast.
• Optolong L-Pro: a true broadband filter that aims to preserve the natural colours of stars in the night sky.
• Astronomik CLS-CCD: a favourite among amateur astrophotographers, this filter creates strong contrast between the nebula and a bright sky.
• Antlia Triband RGB Ultra II: this filter focuses on the important RGB bands, making it a versatile choice for capturing galaxies, reflection nebulae and star clusters, even from highly polluted skies.
• Astro Hutech IDAS Nebula Booster NB1: similar to the Optolong L-eNhance, this filter collects light in the H-alpha and OIII areas of the visible spectrum.
• Baader Moon and Skyglow: a mild light pollution filter that allows natural colours to pass through, making it a good choice for broadband targets.
• Optolong L-Ultimate: this filter enhances contrast by blocking all light, including wavelengths from mercury and sodium street lights, but at the expense of natural star colours.

While light pollution filters can be a useful tool for astrophotography in light-polluted areas, they are not always necessary. In some cases, it may be more effective to drive to a darker location or invest in a monochrome camera with narrowband filters. Additionally, light pollution filters may not be effective against LED street lights, which are becoming increasingly common.

Light pollution filters for monochrome cameras

Light pollution filters can be used with monochrome cameras to enhance astrophotography. Light pollution is a common issue for photographers located near urban centres, as light from cities and companies can interfere with the visual spectrum.

LRGB filters are not as effective in light-polluted areas, as they depend on taking a very deep and high-quality L image, which is then coloured using lower-quality R, G, and B data. Light pollution can cause issues with the L image, as it interferes with the wavelengths of light, making it difficult to capture the full spectrum of colours.

Instead, narrowband imaging works well for nebulae since high-quality 3 nm filters can eliminate most city light and moonlight. Narrowband filters are much more precise, allowing only a few nm of light through, which blocks most light pollution and moonlight while allowing only specific wavelengths through.

Photographers can also consider using photometric filters, which are more narrow than regular LRGB filters, particularly in the Luminance (L) filter, which captures the entire visible band. This approach is similar to using "Skylight" and "UHC" filters for visual work, where the idea is to let enough useful light through while excluding light pollution.

Another option is to replace the L (UV/IR) filter with a light pollution filter, such as the Astronomik or Optolong CLS CCD filter, or the IDAS LPS D2 if you have white LEDs in your area. This can help cut out artificial light pollution and increase contrast in images.

It is worth noting that LED lights are becoming more common and these emit broadband light, so light pollution filters that target specific sodium bands may not be as effective.

Broadband filters

CLS (City Light Suppression) filters are a type of broadband filter. They block light in selected sections of the spectrum, coinciding with the emissions from artificial light sources, as well as natural sky brightness. This makes the sky background appear darker, and the object being observed stand out more clearly.

Narrowband filters

The width of the bandpass in a narrowband filter is measured in nanometres and determines how much of the spectrum the filter permits to pass through. Narrowband filters have a narrow bandpass, typically between 3 and 12nm, while RGB filters transmit about 100nm of light. This very narrow range in narrowband filters blocks most light, hence why they are useful in light-polluted areas.

When it comes to purchasing narrowband filters, there are a variety of brands to choose from, including Optolong, ZWO, Baader, Astronomik, and Astrodon. Astrodon is considered the best choice but is also the most expensive, with individual filters costing nearly $600 each. ZWO filters are considered "budget-friendly" and are a good starting point for beginners.

When deciding which narrowband filters to buy, you should also consider the size of the filters. The most common sizes are 1.25”, 2”, 31mm, and 36mm. The 1.25” and 2” filters usually have threads, so they can be easily installed on your filter wheel, camera, or telescope. The 31mm and 36mm filters don't have threads, so they must be installed differently, which can be more challenging.

In addition to the filters themselves, you will also need a filter wheel, which allows you to quickly swap between filters without having to take apart your entire setup. ZWO offers a range of filter wheels that can be controlled by the ASIAir app on your phone.

Overall, narrowband filters are a valuable tool for astrophotographers, especially those shooting in light-polluted areas. They allow you to capture detailed images of nebulae and other celestial objects by isolating specific wavelengths of light.

Dual bandpass filters

Optical filters and dichroics are components used to transmit or block specific wavelengths of light to control light in an optical system. They operate based on thin-film interference, where multiple layers of dielectric materials with varying refractive indices are deposited on a substrate through evaporation or sputtering. This results in the selective reflection and transmission of different wavelengths.

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