On the AQ637X Series OSA Why is the Actual Resolution Not the Set Value?

The resolution is controlled by 3 factors:

1. Input Slit
2. Detraction Grating 
3. Output Slit

The resolution setting controls the output slit disk. This disk has a fixed number of slits in it. Since the setting only control one of the factors that determines the resolution, and the disk has a fixed number of slits, the set value may not always be the actual resolution. Keep in mind the OSA does calculate actual resolution and displays it on the soft key where you select the resolution you want. Also note that sometimes the actual resolution is better than the selected and sometimes it is not. Please view the atached PowerPoint slides that explain how the OSA resolution works.