Measuring BFL / FFL

• Slide the microscope forward until the actual glass surface of the lens is in focus (BFL), or the mounting surface of the lens is in focus (FFL).
  
  It can be difficult to find the glass surface, especially if it is really clean. Fortunately there is usually at least one speck of dust on the surface. It is helpful to remove the fiber optic bundle from the collimator and shine it directly on the lens surface at this stage too. This will cause any dust particles to light up brightly.
  
  It is also helpful to focus on something easy to find (like the mounting surface) first.
• Set the digital micrometer to zero
• Slide the microscope back until the image is in focus.
• Read BFL (EFL) from the dial micrometer

Wells Research can supply optional digital indicators ranging from 0-1 inch travel to 0-18 inches travel.