Please note: The current batch of this filter does not mention Thousand Oaks' name or any other info on the filter cell as shown in our photo above. Nothing is imprinted on the filter cell. However, this is a brand new, original item as received from Thousand Oaks.
- Provides light pollution rejection when viewing diffuse, emission, and planetary nebulae
- Passes 93% of the light emitted by these object types
- Very narrow bandpass on just the ~496nm and ~501nm spectral emission lines
- Improves nebular clarity and contrast
Oxygen III (OIII) filters are sometimes referred to as light pollution rejection (LPR) filters but their effect goes beyond the reduction of light pollution alone. This OIII filter is a bandpass filter that allows only a small portion of light in the visual doubly-ionized O-III portion of the light spectrum to be passed through the filter glass.
This filter will pass only a very small emission line centered at the ~496nm and ~501nm OIII lines. This is 93% of the spectrum of light usually emitted by diffuse, emission, and planetary nebulae. By rejecting most other light certain nebula will appear more clearly with sharper contrast against a blacker sky.