Optolong H-Beta nanofilter 12 nm 2 inch for visual observation of fog

Some faint nebulae shine mainly in the H-beta line of hydrogen and remain almost invisible without a filter. With the Optolong H-beta 2 inch, you only let a narrow band of 12 nm through around that line, so those nebulae become more visible as the background darkens. Well-known targets are the Horsehead Nebula in Orion and the California Nebula in Perseus.

The 2 inch size is useful if you use 2 inch eyepieces, or if you use the filter in a 2 inch diagonal mirror screws and combines them with all your eyepieces.

Large nebulae like the California Nebula fit better into the image at low magnification with a 2 inch eyepiece. First check that you have diagonal or 2 inch eyepiece filter thread. For more targets for a dark night see our guide on deep-sky objects.

If you work with 1.25-inch eyepieces only, then the H-beta in 1.25 inch the logical choice.