Filter

Overview of Typical Filter Sets

 

The excitation filter (also called the exciter) transmits only those wavelengths of the illumination light that efficiently excite a specific dye. The emission filter (barrier filter or emitter) attenuates all of the light transmitted by the excitation filter and very efficiently transmits any fluorescence emitted by the specimen. The dichroic beamsplitter (dichroic mirror or dichromatic beamsplitter) is a thin piece of coated glass set at a 45-degree angle to the optical path of the microscope.

Tyfical filter set
Band pass filters are designed to transmit a specific range of wavelengths and block light on either side of that range. These filters are denoted by their center wavelength and bandwidth. The center wavelength (CWL) is the arithmetic mean of the wavelengths at 50% of peak transmission. The full width at half maximum (FWHM) is the bandwidth at 50% of peak transmission.

 

Schematic of Typical Filter Cube

The schematic of a typical filter cube for an inverted microscope is illustrated like below.

The primary filtering element in a fluorescence microscope is the set of three filters housed in a fluorescence filter cube (or filter block): the excitation filter, the emission filter, and the dichroic beamsplitter.

 

Multi Band Filter Set

One filter configuration is a set including a multi band exciter, multi band dichroic, and multi band emission filter. Each filter can be created to selectively transmit and block multiple bands of wavelengths.

 

One filter configuration is a set including a multiband exciter, multiband dichroic, and multiband emission filter. Each filter can be created to selectivly transmit and block multiple bands of wavelengths. This configuration requires the user to use a color CCD camera and simultaneously capture multiple fluorochromes present in a sample with a single image.

 This configuration requires the user to use a color CCD camera and simultaneously capture multiple fluorochromes present in a sample with a single image.

Filter Characteristics

  •  Bandpass filters are designed to transmit a specific range of wavelengths and block light on either side of that range by their center wavelength and bandwidth.
  •  LP and SP filters are denoted by their cut-on or cut-off wavelengths at 50% of peak transmission. LP or SP filters that have a very sharp slope.

LP and SP filters are denoted by their cut-on or cut-off wavelengths at 50% of peak transmission. LP or SP filters that have a very sharp slope.

  • Neutral Density (ND) filter blocks all wavelengths of light evenly.  

 

Fluorescence Microscope

This image is a schematic diagram of a typical fluorescence microscope, which uses incident-light illumination. This is the most common type of fluorescence microscope. Its most important feature is that by illuminating
with incident light it need only filter out excitation light scattering back from the specimen or reflecting from glass surfaces.

 

Schematic of a wide-field fluorescence microscope, showing the separate optical paths for illuminating the specimen and imaging the specimen
Schematic of a wide-field fluorescence microscope, showing the separate optical paths for illuminating the specimen and imaging the specimen

Image Gallery

 

OPTICS FOR MICROSCOPE