Chroma 3nm OIII Ultra Narrowband Filter

Chroma 3nm OIII Ultra Narrowband Filter

  (2 Reviews)
✓ 2 year warranty


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About this product

Model:  chroma_oiii_3nm_36
Part Number:  CT-27006-36D

Premium quality, ULTRA-narrowband 3nm OIII Filter

Chroma’s OIII filters isolate the 500.7nm primary emission line of doubly ionised oxygen. After H-alpha, this is the next most common emission when imaging nebulae

Chroma Technology is an employee-owned company based in Vermont, USA. Chroma manufacture the highest quality astronomy filters with durable, sputtered hard coatings using single substrates of the best glass, eliminating the need for laminations. All primary filter coatings are applied on the front surface and anti-reflection coatings on the rear surface to prevent ghosting and to maximise transmission. Chroma astronomical filters are used worldwide in research and amateur applications. 

Highly precise and accurate, the passbands of these filters remain spectrally stable and do not drift in response to extreme temperature fluctuations or changes in humidity.

All filters may be used with focal ratios of f/4 or slower. For optics faster than f/4 then due to the spectral shift we recommend using the 5nm filters instead.


  • CWL: 500.7nm, Bandwidth: 3nm
  • Durable sputter coatings
  • Parallelism: <30 arcsec
  • Thickness: 3.0 +/-0.05mm
  • Filters designed for use with CCD and for f/4.0 or slower
  • Transmitted wavefront better than 0.25 waves/inch
  • No reflections leading to image distortions or ‘back reflections’

Transmission Chart

Cleaning and Handling

Handle coated pieces by the edges only. Clean gently only if necessary. Loose particles should be removed with a bulb puffer or filtered, pressurised air cleaner. If necessary, gently wipe surface using anhydrous alcohol and lint-free lab towels. Use new surface of towel with each wipe.


Orientation Instructions

Proper orientation of the filter is necessary in order to minimise autofluorescence and maximise performance. There is a caret (arrow) located on the edge of each filter in order to aid orientation. Excitation (x) filters should be positioned with the arrow pointing toward the specimen, toward the inside of the cube, and away from the light source. Emission (m) filters should be placed with the arrow pointing toward the specimen, toward the inside of the cube, and away from the detector/eye. Dichroic mirrors should be mounted with the coated surface toward the light source, excitation filters, and the specimen. The dichroics either have an arrow on the side pointing to the coated side, or they are beveled on the coated side. The beveled side is the smaller surface.

Customer reviews

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OIII 3nm versus Baader 8.5nm
31 August 2020  | 

Not a fair comparison. A better one would be versus the Baader 3.5nm but alas I don't have that filter so I can't directly compare them. I can compare it with the Baader 8.5nm OIII which I do have and it's night and day in light polluted skies. Even with the moon at 86% the other night I got clean data. Previously that would have been washed out with moon glow. Highly recommend as an upgrade to the Baader 8.5nm. No halo's around bright stars is another benefit.

Rating (max 5):  
Great filters!
26 March 2020  | 

I just got to use these 3nm filters (set). My original filters were Baarder OIII8.5 ,ha7 & zwo sii7 which is not bad, but these filter are in another league. Iím very happy with my purchase 🙂


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