Chroma OIII filter, 5nm FWHM


  • H-alpha filters are essential for imaging nebulae and other objects which are rich in ionized hydrogen.
  • At 656.3nm, a narrow-band emission filter is required to separate H-alpha from the SII doublet (671.6nm and 673.1nm).
  • Parfocal for systems f/4.0 or slower
  • Transmitted wavefront better than 0.25 waves/inch
  • Parallelism: less than 30 arcsec
  • Made in the U.S.A.
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Chroma’s OIII filters isolate the 500.7nm primary emission line of doubly ionized oxygen. After H-alpha, this is the next most common emission when imaging nebulae.

Weight .3125 lbs
Dimensions 3 × 3 × 3 in
Filter Size

Chroma 1.25" Mounted 5nm OIII – CH_OIII_125R – $460, Chroma 2" round mounted 5nm OIII – CH_OIII5_2R – $740, Chroma 5nm OIII unmounted 31mm – CH_OIII5_31R – $465, Chroma 36mm Unmounted 5nm OIII – CH_OIII5_36R – $620, Chroma 50mm diameter round, unmounted 5nm OIII – CH_OIII5_50R – $725, Chroma 50mm square Unmounted 5nm OIII – CH_OIII5_50S – $725, Chroma 65mm square Unmounted 5nm OIII – CH_OIII5_65S – $1195

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