SII filters isolate the emission from ionized Sulfur atoms, also common in nebulae. Emission is at two lines occurring as a doublet, at 671.6 and 673.1 nm.
- Parfocal for systems f/4.0 or slower
- Transmitted wavefront better than 0.25 waves/inch
- Parallelism: less than 30 arcsec
- Made in America
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