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