The Genesys-20 Spectrophotometer, shown here complete with a computer system, provides a simple tool to analyze filters. To use the unit, power it on and wait until ready (about 5 minutes). Press the A/T/C button to select % Transmission on the display. Insert the filter to be analyzed into the filter holder.

• Press nm-Up or nm-Down to select the wavelength on the display.
• Remove the filter holder and close the sample door.
• Press the 100%T button. The unit will display 'Setting Blank ...' and then display 100%
• Insert the sample holder into the unit and close the sample door.
• Read the transmission of the filter at that wavelength directly as displayed on the LCD.

The above procedure (beginning with selecting wavelength) must be repeated for each reading required. Start taking readings across the entire spectrum at 25 nm apart then take more readings at 5 nm intervals around the peak transmission (to precisely determine center wavelength for the filter). As well, take readings near the half-maximum point to allow a precise determination of the FWHM of the filter.

The Genesys-20 Controls (including wavelength selector, ZERO button, and units selection) as well as the filter holder for the unit with a dielectric filter installed.

Note that the above procedure is not optimal (as discussed in class). The "proper" procedure consists of inserting a glass blank into the sample holder in order to reference the percent transmission of the filter itself minus the transmission of the glass blank. In order to simplify the procedure and preserve the integrity of the fragile coating we will leave the filter in it's holder and use a thin substrate to reduce effects of the substrate on measurements.