What does "CLS" mean on the Explore Scientific 2.0" filter?
CLS stands for City Light Suppression. The Explore Scientific CLS filter is designed to combat light pollution by blocking the primary wavelengths of light emitted by common streetlights (like mercury-vapor and sodium-vapor lamps), while transmitting the light from deep-sky objects. This darkens the sky background and increases contrast.
Is the Explore Scientific 2.0" CLS filter better than a UHC filter?
Neither is "better," they are designed for different purposes. The CLS filter is a broadband filter, making it more versatile for a range of objects including nebulae, galaxies, and star clusters. The UHC (Ultra High Contrast) filter is a narrowband filter that provides more extreme contrast on specific emission and planetary nebulae, but is less effective on broadband targets. For a first or all-purpose filter, the CLS is often recommended.
How will the Explore Scientific CLS filter perform on the Orion Nebula (M42) in my 8" Dobsonian?
It will perform very well. In an 8" telescope, the CLS filter will significantly darken the sky around the Orion Nebula (M42), making the faint outer loops of nebulosity more visible. You'll notice much greater contrast in the Trapezium region and better definition in the "wings" of the nebula, even from a suburban backyard.
Will the 2.0" CLS filter help me see galaxies from my city backyard?
Yes, it will help, but the effect is more subtle than on nebulae. The CLS filter will darken the skyglow surrounding the galaxy, which improves the contrast and can make the faint core easier to spot. However, since galaxies emit light across the entire spectrum (broadband), the filter will also slightly dim the galaxy itself. It makes finding and framing the galaxy easier against a polluted sky.
Can I use the Explore Scientific CLS filter for astrophotography?
Yes, the CLS filter is a popular choice for beginner to intermediate astrophotographers using color cameras (DSLR, Mirrorless, or One-Shot-Color astro cameras). It helps to control light pollution gradients and brings out more detail in emission nebulae. For advanced imaging, multi-bandpass or narrowband filters are typically used, but the CLS provides a major improvement over unfiltered imaging from the city.
Where do I install the Explore Scientific 2.0" filter in my optical train?
The filter has standard 2-inch filter threads (M48x0.75). You can screw it directly into the barrel of any 2-inch eyepiece, a 2-inch diagonal, or a 2-inch camera nosepiece. For visual use, attaching it to the eyepiece is the most common method.
