Used Baader O-III 2" f/2 Ultra-Highspeed CMOS Optimized 4nm Filter


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  • $299.95
  • Regular price $414.00

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This is a Baader O-III 2" filter in excellent condition.  The optics and body are clean.  It comes in it's original jewel case.  





Baader has designed this 2" OIII ultra-highspeed filter to be precision-grade and provide astrophotographers an excellent complement to their imaging setup. OIII narrowband filters isolate just the two doubly-ionized oxygen lines emitted by planetary and emission nebulae and block the rest of the overall spectrum of light. This results in extreme contrast between the black sky background and the faint photons of OIII light needed for detailed views of the Veil, Ring, Dumbbell, Crescent and Orion nebulae, and other objects.

With 4 nm FWHM, this filter from Baader is ultra-highspeed and is recommended for extremely fast optical systems from f/3.4 to f/1.8, like the Celestron RASA astrographs. The filters are designed to allow for 1:1:1 exposures. This matches the typical CMOS quantum efficiency and s/n ratio.

This Baader Planetarium OIII f/2 ultra-highspeed filter is CMOS optimized with Life-Coat. This coating is a hard coating that will not peel, flake, and will not physically degrade even in the most extreme weather conditions. This coating is also designed to withstand repeated cleaning with fine optical cleaning equipment. This coating is so durable that Baader is confident it will last the life of the filter.

Not only do the filters have sealed coating edges with the Life-Coat, but they are also individually hard coated with Reflex-Blocker and planoptically polished. All of the edges are blackened for increased contrast and eliminate any reflection that would come from light falling on the edge of the filter. The filters are also equipped with a filter-lead-side-indicator in the form of a frontside outer rim. The filters are optimized for CMOS cameras, but they work great with CCD cameras as well.

Baader Ultra-Highspeed 2" CMOS Optimized Filter Features

  • Transmission Ranges: OIII
  • Filter Thickness (w/out glass) 2 mm
  • Half Bandwidth: 4 nm
  • Central Wavelenth: 500.7 nm
  • AR-Coating: Reflex Blocker hard coated and planoptically polished
  • Filter Size: 2"
  • Threaded: Yes
  • Usage: CMOS, CCD, OIII
  • Mounted: Yes
  • Filter Type: Narrowband
  • FIlter Shape: Round
  • Feature Highlight: CMOS-Optimized with Life-Coat
Product specification
SKU Number
Model Number
Single Filter, Set, or Accessory
Single Filter
Filter Type
Filter Size
50.8mm (2")
Filter Shape
Filter Insert Style
Baader Model Number

Filter Wavelength (Center or Range)
500.7 nm
Filter Bandwidth/Bandpass
4 nm
Filter Optical Thickness
2 mm

Baader - Limited Lifetime