Dual-Narrowband Filters

Reference: Dual Narrowband Filters Shootout: Optolong L-eNhance vs. Antlia ALP-T vs. Optolong L-eXtreme

Overview

• Used to photograph emission nebulae from light-polluted cities using color cameras (DSLRs or dedicated astrophotography cameras)
  • Emission nebulae are nebulae that emit their own light from ionized atoms associated with the different gases in the gas clouds (hydrogen, oxygen, and sulfur)
  • These clouds of gas emit very specific wavelengths of light that filters can be designed to pass
• Isolate light from emission nebulae, specifically the O3 and H-alpha emission line
• Pass light at specific parts of the visible spectrum
• How much of the light they pass is called the band pass
  • Anything not included in the band pass is blocked
• Also work for blocking light pollution

What they are NOT good for

• Anything other than emission nebulae
• Natural star color
• Reflection nebulae
• Other galaxies (might be possible if the galaxy has a lot of emission nebulae like M33)
  • Galaxies are typically taken with broadband filters, not narrowband filters

Popular Filters

• Optolong L-Enhance ($229)
• Optolong L-Extreme ($309)
• Antlia ALP-T ($380)

Spectral Measurement

• All three filters are well centered on the emission line, but the more expensive filters have the tighter band passes