| abstract |
The invention relates to optical filters comprising an opacified portion. In particular, fire polishing certain optical filters results in darkening of the fire polished region. The darkening opacifies the ottical filter at the fire polished portion resulting in such portion having a substantially lower transmission of light, such as at wavelengths of grater than 300 nm. An adhesive, employed to bon a fitting (e.g. threaded ring) of an illuminator to an optical filter, is not exposed to the light absorbed by the opacified portion filter, leading to extended durabillity. The optical filters are preferably suitable for use in illuminators for weathering devices. |