Long-Pass (Viewing) Filter
Definition
An optical filter transmitting all wavelengths above a defined cut-on wavelength; worn as goggles by the examiner to block excitation light while seeing fluorescence emission.
- Function
- Transmits all wavelengths above a cut-on point
- Blocks
- Excitation light
- Form factor
- Goggles worn by the examiner
- Purpose
- View fluorescence emission
Common questions
Why must the viewing filter block the excitation light specifically?+
Without blocking it, the far more intense excitation light would overwhelm the much weaker fluorescence emission, making the fluorescing evidence effectively invisible to the examiner.
How is a long-pass filter's cut-on wavelength chosen for an examination?+
It is selected to sit just above the wavelength of the excitation light source, so it passes the emitted fluorescence through while blocking the reflected excitation light itself.
Related terms
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